Table of contents

Sixteen pulsars have been discovered so far in blind searches of photons collected with the Large Area Telescope on the Fermi Gamma-ray Space Telescope. We here report the discovery of radio pulsations from two of them. PSR J1741–2054, with period P = 413 ms, was detected in archival Parkes telescope data and subsequently has been detected at the Green Bank Telescope (GBT). Its received flux varies greatly due to interstellar scintillation and it has a very small dispersion measure of DM = 4.7 pc cm⁻³, implying a distance of ≈0.4 kpc and possibly the smallest luminosity of any known radio pulsar. At this distance, for isotropic emission, its gamma-ray luminosity above 0.1 GeV corresponds to 28% of the spin-down luminosity of $\dot{E} = 9.4\times 10^{33}$ erg s⁻¹. The gamma-ray profile occupies 1/3 of pulse phase and has three closely spaced peaks with the first peak lagging the radio pulse by δ = 0.29 P. We have also identified a soft Swift source that is the likely X-ray counterpart. In many respects PSR J1741–2054 resembles the Geminga pulsar. The second source, PSR J2032+4127, was detected at the GBT. It has P = 143 ms, and its DM = 115 pc cm⁻³ suggests a distance of ≈3.6 kpc, but we consider it likely that it is located within the Cyg OB2 stellar association at half that distance. The radio emission is nearly 100% linearly polarized, and the main radio peak precedes by δ = 0.15 P the first of two narrow gamma-ray peaks that are separated by Δ = 0.50 P. The second peak has a harder spectrum than the first one, following a trend observed in young gamma-ray pulsars. Faint, diffuse X-ray emission in a Chandra image is possibly its pulsar wind nebula. The wind of PSR J2032+4127 is responsible for the formerly unidentified HEGRA source TeV J2032+4130. PSR J2032+4127 is coincident in projection with MT91 213, a Be star in Cyg OB2, although apparently not a binary companion of it.

An analysis of archival mid-infrared (mid-IR) spectra of Seyfert galaxies from the Spitzer Space Telescope observations is presented. We characterize the nature of the mid-IR active nuclear continuum by subtracting a template starburst spectrum from the Seyfert spectra. The long wavelength part of the spectrum contains a strong contribution from the starburst-heated cool dust; this is used to effectively separate starburst-dominated Seyferts from those dominated by the active nuclear continuum. Within the latter category, the strength of the active nuclear continuum drops rapidly beyond ∼20 μm. On average, type 2 Seyferts have weaker short-wavelength active nuclear continua as compared to type 1 Seyferts. Type 2 Seyferts can be divided into two types, those with strong polycyclic aromatic hydrocarbon (PAH) bands and those without. The latter type show polarized broad emission lines in their optical spectra. The PAH-dominated type 2 Seyferts and Seyfert 1.8/1.9s show very similar mid-IR spectra. However, after the subtraction of the starburst component, there is a striking similarity in the active nuclear continuum of all Seyfert optical types. PAH-dominated Seyfert 2s and Seyfert 1.8/1.9s tend to show weak active nuclear continua in general. A few type 2 Seyferts with weak/absent PAH bands show a bump in the spectrum between 15 and 20 μm. We suggest that this bump is the peak of a warm (∼200 K) blackbody dust emission, which becomes clearly visible when the short-wavelength continuum is weaker. This warm blackbody emission is also observed in other Seyfert optical subtypes, suggesting a common origin in these active galactic nuclei.

Echelle spectra of HD 183143 [B7Iae, E(B − V) = 1.27] were obtained on three nights, at a resolving power R = 38,000 and with a signal-to-noise ratio ≈ 1000 at 6400 Å in the final, combined spectrum. A catalog is presented of 414 diffuse interstellar bands (DIBs) measured between 3900 and 8100 Å in this spectrum. The central wavelengths, the widths (FWHM), and the equivalent widths of nearly all of the bands are tabulated, along with the minimum uncertainties in the latter. Among the 414 bands, 135 (or 33%) were not reported in four previous, modern surveys of the DIBs in the spectra of various stars, including HD 183143. The principal result of this study is that the great majority of the bands in the catalog are very weak and fairly narrow. Typical equivalent widths amount to a few mÅ, and the bandwidths (FWHM) are most often near 0.7 Å. No preferred wavenumber spacings among the 414 bands are identified which could provide clues to the identities of the large molecules thought to cause the DIBs. At generally comparable detection limits in both spectra, the population of DIBs observed toward HD 183143 is systematically redder, broader, and stronger than that seen toward HD 204827 (Paper II). In addition, interstellar lines of C₂ molecules have not been detected toward HD 183143, while a very high value of N(C₂)/E(B − V) is observed toward HD 204827. Therefore, either the abundances of the large molecules presumed to give rise to the DIBs, or the physical conditions in the absorbing clouds, or both, must differ significantly between the two cases.

We identify 3113 highly variable objects in 7200 deg² of the Palomar-QUEST (PQ) Survey, which each varied by more than 0.4 mag simultaneously in two broadband optical filters on timescales from hours to roughly 3.5 years. The primary goal of the selection is to find blazars by their well-known violent optical variability. Because most known blazars have been found in radio and/or X-ray wavelengths, a sample discovered through optical variability may have very different selection effects, elucidating the range of behavior possible in these systems. A set of blazars selected in this unusual manner will improve our understanding of the physics behind this extremely variable and diverse class of active galactic nucleus (AGN). The object positions, variability statistics, and color information are available using the PQ CasJobs server. The time domain is just beginning to be explored over large sky areas; we do not know exactly what a violently variable sample will hold. About 20% of the sample has been classified in the literature; over 70% of those objects are known or likely AGNs. The remainder largely consists of a variety of variable stars, including a number of RR Lyrae and cataclysmic variables.

The extreme outer Galaxy (EOG), the region with a Galactic radius of more than 18 kpc, is known to have a very low metallicity, about one-tenth that of the solar neighborhood. We obtained the deep near-infrared (NIR) images of two very young (∼0.5 Myr) star-forming clusters that are two of the most distant embedded clusters in the EOG. We find that in both clusters the fraction of stars with NIR excess, which originates from the circumstellar dust disk at radii of ⩽0.1 AU, is significantly lower than those in the solar neighborhood. Our results suggest that most of the stars forming in the low-metallicity environment experience disk dispersal at an earlier stage (<1 Myr) than those forming in the solar metallicity environment (as much as ∼5–6 Myr). Such a rapid disk dispersal may make the formation of planets difficult, and the shorter disk lifetime with a lower metallicity, could contribute to the strong metallicity dependence of the well-known "planet–metallicity correlation," which states that the probability of a star hosting a planet increases steeply with stellar metallicity. The reason for the rapid disk dispersal could be the increase of the mass accretion rate and/or the effective far-ultraviolet photoevaporation due to the low extinction; however, another unknown mechanism for the EOG environment could be contributing significantly.

Star formation in relic H ii regions of the first stars is investigated using magnetohydrodynamical simulations with a nested-grid method that covers ∼10 orders of magnitude in spatial scale and ∼20 orders of magnitude in density contrast. Due to larger fraction of H₂ and HD molecules, its prestellar thermal evolution is considerably different from that in the first star formation. Reflecting the difference, two hydrostatic cores appear in a nested manner: a protostar is enclosed by a transient hydrostatic core, which appears during the prestellar collapse. If the initial natal core rotates fast at a rate with rotational to gravitational energy ratio β₀ ≳ 0.01–0.1, the transient hydrostatic core fragments to ∼10 M_☉ subcores at density ∼10⁹ cm⁻³. With smaller rotation energy, fragmentation occurs at higher density while a single protostar forms without fragmentation if rotation is extremely slow with β₀ ≲ 10⁻⁶ to 10⁻⁵. If magnetic field is present, these threshold values of β₀ are boosted owing to angular momentum transport by the magnetic breaking. Magnetic field also drives the protostellar outflows. With strong magnetic field, two distinct outflows are observed: the slower one emanates from the transient hydrostatic core, while the faster one from the protostar. These flows may affect the final stellar mass by ejecting some of masses in the initial core, and also may play some role in driving and maintenance of interstellar turbulence in young galaxies.

We carried out an unbiased, spectroscopic survey using the low-resolution module of the infrared spectrograph (IRS) onboard Spitzer targeting two 2.6 square arcminute regions in the GOODS-North field. The IRS was used in a spectral mapping mode with 5 hr of effective integration time per pixel. One region was covered between 14 and 21 μm and the other between 20 and 35 μm. We extracted spectra for 45 sources. About 84% of the sources have reported detections by GOODS at 24 μm, with a median f_ν(24 μm) ∼ 100 μJy. All but one source are detected in all four IRAC bands, 3.6 to 8 μm. We use a new cross-correlation technique to measure redshifts and estimate IRS spectral types; this was successful for ∼60% of the spectra. Fourteen sources show significant polycyclic aromatic hydrocarbon emission, four mostly SiO absorption, eight present mixed spectral signatures (low PAH and/or SiO) and two show a single line in emission. For the remaining 17, no spectral features were detected. Redshifts range from z ∼ 0.2 to z ∼ 2.2, with a median of 1. IR luminosities are roughly estimated from 24 μm flux densities, and have median values of 2.2 × 10¹¹L_☉ and 7.5 × 10¹¹L_☉ at z ∼ 1 and z ∼ 2, respectively. This sample has fewer active galactic nuclei than previous faint samples observed with the IRS, which we attribute to the fainter luminosities reached here.

We have observed 152 nearby solar-type stars with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. Including stars that met our criteria but were observed in other surveys, we get an overall success rate for finding excesses in the long-wavelength IRS band (30–34 μm) of 11.8% ± 2.4%. The success rate for excesses in the short-wavelength band (8.5–12 μm) is ∼1% including sources from other surveys. For stars with no excess at 8.5–12 μm, the IRS data set 3σ limits of around 1000 times the level of zodiacal emission present in our solar system, while at 30–34 μm data set limits of around 100 times the level of our solar system. Two stars (HD 40136 and HD 10647) show weak evidence for spectral features; the excess emission in the other systems is featureless. If the emitting material consists of large (10 μm) grains as implied by the lack of spectral features, we find that these grains are typically located at or beyond the snow line, ∼1–35 AU from the host stars, with an average distance of 14 ± 6 AU; however, smaller grains could be located at significantly greater distances from the host stars. These distances correspond to dust temperatures in the range ∼50–450 K. Several of the disks are well modeled by a single dust temperature, possibly indicative of a ring-like structure. However, a single dust temperature does not match the data for other disks in the sample, implying a distribution of temperatures within these disks. For most stars with excesses, we detect an excess at both IRS and Multiband Imaging Photometer for Spitzer (MIPS) wavelengths. Only three stars in this sample show a MIPS 70 μm excess with no IRS excess, implying that very cold dust is rare around solar-type stars.

We present the first broadband λ = 1 mm spectrum toward the z = 2.56 Cloverleaf quasar, obtained with Z-Spec, a grating spectrograph on the 10.4 m Caltech Submillimeter Observatory. The 190–305 GHz observation band corresponds to the rest frame 272–444 μm, and we measure the dust continuum as well as all four transitions of carbon monoxide (CO) lying in this range. The power-law dust emission, F_ν = 14 mJy(ν/240 GHz)^3.9 is consistent with the published continuum measurements. The CO J = 6 → 5, J = 8 → 7, and J = 9 → 8 measurements are the first, and now provide the highest-J CO information in this source. Our measured CO intensities are very close to the previously published interferometric measurements of J = 7 → 6, and we use all available transitions and our ¹³CO upper limits to constrain the physical conditions in the Cloverleaf molecular gas disk. We find a large mass (2–50 × 10⁹ M_☉) of highly excited gas with thermal pressure nT > 10⁶ K cm⁻³. The ratio of the total CO cooling to the far-IR dust emission exceeds that in the local dusty galaxies, and we investigate the potential heating sources for this bulk of warm molecular gas. We conclude that both UV photons and X-rays likely contribute, and discuss implications for a top-heavy stellar initial mass function arising in the X-ray-irradiated starburst. Finally, we present tentative identifications of other species in the spectrum, including a possible detection of the H₂O \2_0,2 → 1_1,1 transition at λ_rest = 303 μm.

Using a source selection biased toward high-mass star-forming regions, we used a large velocity gradient code to calculate the H₂ densities and CS column densities for a sample of Midcourse Space Experiment 8 μm infrared dark cores. Our average H₂ density and CS column density were 1.14 × 10⁶cm⁻³ and 1.21 × 10¹³ cm⁻², respectively. In addition, we have calculated the Jeans mass and Virial mass for each core to get a better understanding of their gravitational stability. We found that core masses calculated from observations of N₂H⁺J = 1→0 and C¹⁸O J = 1→0 by Ragan et al. (Paper I) were sufficient for collapse, though most regions are likely to form protoclusters. We have explored the star-forming properties of the molecular gas within our sample and find some diversity which extends the range of infrared dark clouds from the very massive clouds that will create large clusters, to clouds that are similar to some of our local counterparts (e.g., Serpens, Ophiuchus).

The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M_☉. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, these stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|ΔT_eff|>10³ K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M_☉ will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density ρ_χ = 10⁹ GeV cm⁻³. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.

We compare the CO (J = 1–0) and H i emission in the Large Magellanic Cloud in three dimensions, i.e., including a velocity axis in addition to the two spatial axes, with the aim of elucidating the physical connection between giant molecular clouds (GMCs) and their surrounding H i gas. The CO J = 1–0 data set is from the second NANTEN CO survey and the H i data set is from the merged Australia Telescope Compact Array (ATCA) and Parkes Telescope surveys. The major findings of our analysis are as follows: (1) GMCs are associated with an envelope of H i emission, (2) in GMCs [average CO intensity] ∝ [average H i intensity]^1.1±0.1, and (3) the H i intensity tends to increase with the star formation activity within GMCs, from Type I to Type III. An analysis of the H i envelopes associated with GMCs shows that their average line width is 14 km s⁻¹ and the mean density in the envelope is 10 cm⁻³. We argue that the H i envelopes are gravitationally bound by GMCs. These findings are consistent with a continual increase in the mass of GMCs via H i accretion at an accretion rate of 0.05 M_☉ yr⁻¹ over a timescale of 10 Myr. The growth of GMCs is terminated via dissipative ionization and/or stellar-wind disruption in the final stage of GMC evolution.

The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the 1% level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state, "wCDM", cosmologies. In this paper, we demonstrate that a limited set of only 37 cosmological models—the "Coyote Universe" suite—can be used to predict the nonlinear matter power spectrum to 1% over a prior parameter range set by current cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.

We study a Chandra X-ray Observatory ACIS-S observation of the Galactic globular cluster M12. With a 26 ks exposure time, we detect six X-ray sources inside the half-mass radius (216) of which two are inside the core radius (072) of the cluster. If we assume that these sources are all associated with globular cluster M12, the luminosity L_X among these sources between 0.3 and 7.0 keV varies roughly from 10³⁰ to 10³² erg s⁻¹. For identification, we also analyzed the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and Wide Field and Planetary Camera 2 (WFPC2) data and identified the optical counterparts to five X-ray sources inside the HST ACS field of view. According to the X-ray and optical features, we found 2–5 candidate active binaries (ABs) or cataclysmic variables (CVs) and 0–3 background galaxies within the HST ACS field of view. Based on the assumption that the number of X-ray sources scales with the encounter rate and the mass of the globular cluster, we expect two X-ray sources inside M12, and the expectation is consistent with our observational results. Therefore, the existence of identified X-ray sources (possible CVs or ABs) in M12 suggests the primordial origin of X-ray sources in globular clusters which is in agreement with previous studies.

We present SHARC-II 350 μm imaging of twelve 24 μm bright (F_24 μm > 0.8 mJy) Dust-Obscured Galaxies (DOGs) and Combined Array for Research in Millimeter-wave Astronomy (CARMA) 1 mm imaging of a subset of two DOGs. These objects are selected from the Boötes field of the NOAO Deep Wide-Field Survey. Detections of four DOGs at 350 μm imply infrared (IR) luminosities which are consistent to within a factor of 2 of expectations based on a warm-dust spectral energy distribution (SED) scaled to the observed 24 μm flux density. The 350 μm upper limits for the 8 non-detected DOGs are consistent with both Mrk 231 and M82 (warm-dust SEDs), but exclude cold dust (Arp 220) SEDs. The two DOGs targeted at 1 mm were not detected in our CARMA observations, placing strong constraints on the dust temperature: T_dust > 35–60 K. Assuming these dust properties apply to the entire sample, we find dust masses of ≈3 × 10⁸ M_☉. In comparison to other dusty z ∼ 2 galaxy populations such as submillimeter galaxies (SMGs) and other Spitzer-selected high-redshift sources, this sample of DOGs has higher IR luminosities (2 × 10¹³ L_☉ versus 6 × 10¹² L_☉ for the other galaxy populations) that are driven by warmer dust temperatures (>35–60 K versus ∼30 K) and lower inferred dust masses (3 × 10⁸ M_☉ versus 3 × 10⁹ M_☉). Wide-field Herschel and Submillimeter Common-User Bolometer Array-2 surveys should be able to detect hundreds of these power-law-dominated DOGs. We use the existing Hubble Space Telescope and Spitzer/InfraRed Array Camera data to estimate stellar masses of these sources and find that the stellar to gas mass ratio may be higher in our 24 μm bright sample of DOGs than in SMGs and other Spitzer-selected sources. Although much larger sample sizes are needed to provide a definitive conclusion, the data are consistent with an evolutionary trend in which the formation of massive galaxies at z ∼ 2 involves a submillimeter bright, cold-dust, and star-formation-dominated phase followed by a 24 μm bright, warm-dust and AGN-dominated phase.

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ∼10⁶–10⁷ M_☉ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission. We present here the light curves for all the objects in this sample and the subsequent Hβ time lags for the nine objects where these measurements were possible. The Hβ lag time is directly related to the size of the broad-line region (BLR) in AGNs, and by combining the Hβ lag time with the measured width of the Hβ emission line in the variable part of the spectrum, we determine the virial mass of the central supermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al., which brings the masses determined by reverberation mapping into agreement with the local M_BH–σ_⋆relationship for quiescent galaxies. We also examine the time lag response as a function of velocity across the Hβ line profile for six of the AGNs. The analysis of four leads to rather ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting BLR clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple gravitational infall model. Further investigation will be necessary to fully understand the constraints placed on the physical models of the BLR by the velocity-resolved response in these objects.

High-sensitivity measurements of the linearly polarized solar limb spectrum produced by scattering processes in quiet regions of the solar atmosphere showed that the Q/I profile of the lithium doublet at 6708 Å has an amplitude ∼10⁻⁴ and a curious three-peak structure, qualitatively similar to that found and confirmed by many observers in the Na i D₂ line. Given that a precise measurement of the scattering polarization profile of the lithium doublet lies at the limit of the present observational possibilities, it is worthwhile to clarify the physical origin of the observed polarization, its diagnostic potential, and what kind of Q/I shapes can be expected from theory. To this end, we have applied the quantum theory of atomic level polarization taking into account the hyperfine structure of the two stable isotopes of lithium, as well as the Hanle effect of a microturbulent magnetic field of arbitrary strength. We find that quantum interferences between the sublevels pertaining to the upper levels of the D₂ and D₁ line transitions of lithium do not cause any observable effect on the emergent Q/I profile. Our theoretical calculations show that only two Q/I peaks can be expected, with the strongest one caused by the D₂ line of ⁷Li i and the weakest one due to the D₂ line of ⁶Li i. Interestingly, we find that these two peaks in the theoretical Q/I profile stand out clearly only when the kinetic temperature of the thin atmospheric region that produces the emergent spectral line radiation is lower than 4000 K. The fact that such a thin atmospheric region is located around a height of 200 km in standard semi-empirical models, where the kinetic temperature is about 5000 K, leads us to suggest that the most likely Q/I profile produced by the Sun in the lithium doublet should be slightly asymmetric and dominated by the ⁷Li i peak.

We have used the new 90 GHz MUSTANG camera on the Robert C. Byrd Green Bank Telescope (GBT) to map the bright Huygens region of the star-forming region M42 with a resolution of 9'' and a sensitivity of 2.8 mJy beam⁻¹. Ninety GHz is an interesting transition frequency, as MUSTANG detects both the free–free emission characteristic of the H ii region created by the Trapezium stars, normally seen at lower frequencies, and thermal dust emission from the background OMC1 molecular cloud, normally mapped at higher frequencies. We also present similar data from the 150 GHz GISMO camera taken on the IRAM 30 m telescope. This map has 15'' resolution. By combining the MUSTANG data with 1.4, 8, and 21 GHz radio data from the VLA and GBT, we derive a new estimate of the emission measure averaged electron temperature of T_e = 11376 ± 1050 K by an original method relating free–free emission intensities at optically thin and optically thick frequencies. Combining Infrared Space Observatory–long wavelength spectrometer (ISO–LWS) data with our data, we derive a new estimate of the dust temperature and spectral emissivity index within the 80'' ISO–LWS beam toward Orion KL/BN, T_d = 42 ± 3 K and β_d = 1.3 ± 0.1. We show that both T_d and β_d decrease when going from the H ii region and excited OMC1 interface to the denser UV shielded part of OMC1 (Orion KL/BN, Orion S). With a model consisting of only free–free and thermal dust emission, we are able to fit data taken at frequencies from 1.5 GHz to 854 GHz (350 μm).

We derive structural parameters for ∼2000 globular clusters in the giant Virgo elliptical Messier 87 (M87) using extremely deep Hubble Space Telescope images in F606W (V) and F814W (I) taken with the ACS/WFC. The cluster scale sizes (half-light radii r_h) and ellipticities are determined from point-spread-function -convolved King-model profile fitting. We find that the r_h distribution closely resembles the inner Milky Way clusters, peaking at r_h ≃ 2.5 pc and with virtually no clusters more compact than r_h ≃ 1 pc. The metal-poor clusters have on average an r_h 24% larger than the metal-rich ones. The cluster scale size shows a gradual and noticeable increase with galactocentric distance. Clusters are very slightly larger in the bluer waveband V, a possible hint that we may be beginning to see the effects of mass segregation within the clusters. We also derived a color magnitude diagram for the M87 globular cluster system which shows a striking bimodal distribution.

A bulge–disk decomposition is made for 737 spiral and lenticular galaxies drawn from a Sloan Digital Sky Survey galaxy sample for which morphological types are estimated. We carry out the bulge–disk decomposition using the growth curve fitting method. It is found that bulge properties, effective radius, effective surface brightness, and also absolute magnitude, change systematically with the morphological sequence; from early to late types, the size becomes somewhat larger, and surface brightness and luminosity fainter. In contrast, disks are nearly universal, their properties remaining similar among disk galaxies irrespective of detailed morphologies from S0 to Sc. While these tendencies were often discussed in previous studies, the present study confirms them based on a large homogeneous magnitude-limited field galaxy sample with morphological types estimated. The systematic change of bulge-to-total luminosity ratio, B/T, along the morphological sequence is therefore not caused by disks but mostly by bulges. It is also shown that elliptical galaxies and bulges of spiral galaxies are unlikely to be in a single sequence. We infer the stellar mass density (in units of the critical mass density) to be Ω = 0.0021 for spheroids, i.e., elliptical galaxies plus bulges of spiral galaxies, and Ω = 0.00081 for disks.

We study the relation between size and star formation activity in a complete sample of 225 massive (M_* > 5 × 10¹⁰M_☉) galaxies at 1.5 < z < 2.5, selected from the FIREWORKS UV–IR catalog of the CDFS. Based on stellar population synthesis model fits to the observed rest-frame UV–NIR spectral energy distributions, and independent MIPS 24 μm observations, 65% of the galaxies are actively forming stars, while 35% are quiescent. Using sizes derived from two-dimensional surface brightness profile fits to high-resolution (FWHM_PSF ∼ 045) ground-based ISAAC data, we confirm and improve the significance of the relation between star formation activity and compactness found in previous studies, using a large, complete mass-limited sample. At z ∼ 2, massive quiescent galaxies are significantly smaller than massive star-forming galaxies, and a median factor of 0.34 ± 0.02 smaller than galaxies of similar mass in the local universe. Thirteen percent of the quiescent galaxies are unresolved in the ISAAC data, corresponding to sizes <1 kpc, more than five times smaller than galaxies of similar mass locally. The quiescent galaxies span a Kormendy relation which, compared to the relation for local early types, is shifted to smaller sizes and brighter surface brightnesses and is incompatible with passive evolution. The progenitors of the quiescent galaxies were likely dominated by highly concentrated, intense nuclear starbursts at z ∼ 3–4, in contrast to star-forming galaxies at z ∼ 2 which are extended and dominated by distributed star formation.

The aftermath of supernova (SN) 1987A continues to provide spectacular insights into the interaction between an SN blastwave and its circumstellar environment. We here present 36 GHz observations from the Australia Telescope Compact Array of the radio remnant of SN 1987A. These new images, taken in 2008 April and 2008 October, substantially extend the frequency range of an ongoing monitoring and imaging program conducted between 1.4 and 20 GHz. Our 36.2 GHz images have a diffraction-limited angular resolution of 03–04, which covers the gap between high resolution, low dynamic range VLBI images of the remnant and low resolution, high dynamic range images at frequencies between 1 and 20 GHz. The radio morphology of the remnant at 36 GHz is an elliptical ring with enhanced emission on the eastern and western sides, similar to that seen previously at lower frequencies. Model fits to the data in the Fourier domain show that the emitting region is consistent with a thick inclined torus of mean radius 085, and a 2008 October flux density of 27 ± 6 mJy at 36.2 GHz. The spectral index for the remnant at this epoch, determined between 1.4 GHz and 36.2 GHz, is α = −0.83. There is tentative evidence for an unresolved central source with flatter spectral index.

Recently, a second type of spicules was discovered at the solar limb with the Solar Optical Telescope onboard the Japanese Hinode spacecraft. These previously unrecognized type II spicules are thin chromospheric jets that are shorter lived (10–60 s) and that show much higher apparent upward velocities (of order 50–100 km s⁻¹) than the classical spicules. Since they have been implicated in providing hot plasma to coronal loops, their formation, evolution, and properties are important ingredients for a better understanding of the mass and energy balance of the low solar atmosphere. Here, we report on the discovery of the disk counterparts of type II spicules using spectral imaging data in the Ca ii 854.2 nm and Hα lines with the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope in La Palma. We find rapid blueward excursions in the line profiles of both chromospheric lines that correspond to thin, jet-like features that show apparent velocities of order 50 km s⁻¹. These blueward excursions seem to form a separate absorbing component with Doppler shifts of order 20 and 50 km s⁻¹ for the Ca ii 854.2 nm and Hα line, respectively. We show that the appearance, lifetimes, longitudinal and transverse velocities, and occurrence rate of these rapid blue excursions on the disk are very similar to those of the type II spicules at the limb. A detailed study of the spectral line profiles in these events suggests that plasma is accelerated along the jet, and plasma is being heated throughout the short lifetime of the event.

The current understanding of the turbulent dissipation in stellar convective zones is based on the assumption that the turbulence follows Kolmogorov scaling. This assumption is valid for some cases in which the time frequency of the external shear is high (e.g., solar p modes). However, for many cases of astrophysical interest (e.g., binary orbits, stellar pulsations, etc.), the timescales of interest lie outside the regime of applicability of Kolmogorov scaling. We present direct calculations of the dissipation efficiency of the turbulent convective flow in this regime, using simulations of anelastic convection with external forcing. We show that the effects of the turbulent flow are well represented by an effective viscosity coefficient, we provide the values of the effective viscosity as a function of the perturbation frequency and compare our results to the perturbative method for finding the effective viscosity of Penev et al. that can be applied to actual simulations of the surface convective zones of stars.

We fitted Spitzer/IRS ∼ 2–35 μm spectra of 26 luminous quasi-stellar objects in an attempt to define the main emission components. Our model has three major components: a clumpy torus, dusty narrow-line region (NLR) clouds, and a blackbody-like dust. The models utilize the clumpy torus of Nenkova et al. and are the first to allow its consistent check in type-I active galactic nuclei (AGNs). Single torus models and combined torus–NLR models fail to fit the spectra of most sources, but three-component models adequately fit the spectra of all sources. We present torus inclination, cloud distribution, covering factor, and torus mass for all sources and compare them with bolometric luminosity, black hole mass, and accretion rate. The torus mass is found to be correlated with the bolometric luminosity of the sources. Torus-covering factor may also be (anti-)correlated, if some possibly anomalous points are omitted. We find that a substantial amount of the ∼2–7 μm radiation originates from a hot dust component, which is likely situated in the innermost part of the torus. The luminosity radiated by this component and its covering factor are comparable to those of the torus. We quantify the emission by the NLR clouds and estimate their distance from the center. The distances are ∼700 times larger than the dust sublimation radius, and the NLR-covering factor is about 0.07. The total covering factor by all components is in good agreement with the known AGN type-I:type-II ratio.

We have obtained a full suite of Spitzer observations to characterize the debris disk around HR 8799 and to explore how its properties are related to the recently discovered set of three massive planets orbiting the star. We distinguish three components to the debris system: (1) warm dust (T ∼ 150 K) orbiting within the innermost planet; (2) a broad zone of cold dust (T ∼ 45 K) with a sharp inner edge orbiting just outside the outermost planet and presumably sculpted by it; and (3) a dramatic halo of small grains originating in the cold dust component. The high level of dynamical activity implied by this halo may arise due to enhanced gravitational stirring by the massive planets. The relatively young age of HR 8799 places it in an important early stage of development and may provide some help in understanding the interaction of planets and planetary debris, an important process in the evolution of our own solar system.

We present measurements of Fe, Mg, Si, Ca, and Ti abundances for 388 radial velocity member stars in the Sculptor dwarf spheroidal galaxy (dSph), a satellite of the Milky Way (MW). This is the largest sample of individual α element (Mg, Si, Ca, and Ti) abundance measurements in any single dSph. The measurements are made from Keck/Deep Imaging Multi-Object Spectrometer medium-resolution spectra (6400–9000 Å, R ∼ 6500). Based on comparisons to published high-resolution (R ≳ 20,000) spectroscopic measurements, our measurements have uncertainties of σ[Fe/H] = 0.14 and σ[α/Fe] = 0.13. The Sculptor [Fe/H] distribution has a mean 〈[Fe/H]〉 = −1.58 and is asymmetric with a long, metal-poor tail, indicative of a history of extended star formation. Sculptor has a larger fraction of stars with [Fe/H] < −2 than the MW halo. We have discovered one star with [Fe/H] = −3.80 ± 0.28, which is the most metal-poor star known anywhere except the MW halo, but high-resolution spectroscopy is needed to measure this star's detailed abundances. As has been previously reported based on high-resolution spectroscopy, [α/Fe] in Sculptor falls as [Fe/H] increases. The metal-rich stars ([Fe/H] ∼ −1.5) have lower [α/Fe] than Galactic halo field stars of comparable metallicity. This indicates that star formation proceeded more gradually in Sculptor than in the Galactic halo. We also observe radial abundance gradients of −0.030 ± 0.003 dex arcmin⁻¹ in [Fe/H] and +0.013 ± 0.003 dex arcmin⁻¹ in [α/Fe] out to 11 arcmin (275 pc). Together, these measurements cast Sculptor and possibly other surviving dSphs as representative of the dwarf galaxies from which the metal-poor tail of the Galactic halo formed.

The Parker model for heating of the solar corona involves reconnection of braided magnetic flux elements. Much of this braiding is thought to occur at as yet unresolved scales, for example, braiding of threads within an extreme-ultraviolet or X-ray loop. However, some braiding may be still visible at scales accessible to TRACE or Hinode. We suggest that attempts to estimate the amount of braiding at these scales must take into account the degree of coherence of the braid structure. In this paper, we examine the effect of reconnection on the structure of a braided magnetic field. We demonstrate that simple models of braided magnetic fields which balance the input of topological structure with reconnection evolve to a self-organized critical state. An initially random braid can become highly ordered, with coherence lengths obeying power-law distributions. The energy released during reconnection also obeys a power law. Our model gives more frequent (but smaller) energy releases nearer to the ends of a coronal loop.

We study in detail the mid-infrared (MIR) Spitzer-IRS spectrum of M 87 in the range 5–20 μm. Thanks to the high sensitivity of our Spitzer-IRS spectra we can disentangle the stellar and nuclear components of this active galaxy. To this end, we have properly subtracted from the M 87 spectrum the contribution of the underlying stellar continuum derived from passive Virgo galaxies in our sample. The residual is a clear power law, without any additional thermal component, with a zero-point consistent with that obtained by high spatial resolution, ground-based observations. The residual is independent of the adopted passive template. This indicates that the 10 μm silicate emission shown in the spectra of M 87 can be entirely accounted for by the underlying old stellar population, leaving little room for a possible torus contribution. The MIR power law has a slope α∼0.77–0.82 (S_ν ∝ ν^−α), consistent with optically thin synchrotron emission.

We study the short- and long-term effects of an intermediate mass black hole (IMBH) on the orbits of stars bound to the supermassive black hole (SMBH) at the center of the Milky Way. A regularized N-body code including post-Newtonian terms is used to carry out direct integrations of 19 stars in the S-star cluster for 10 Myr. The mass of the IMBH is assigned one of four values from 400 M_☉ to 4000 M_☉, and its initial semimajor axis with respect to the SMBH is varied from 0.3 to 30 mpc, bracketing the radii at which inspiral of the IMBH is expected to stall. We consider two values for the eccentricity of the IMBH/SMBH binary, e = (0, 0.7), and 12 values for the orientation of the binary's plane. Changes at the level of ∼1% in the orbital elements of the S-stars could occur in just a few years if the IMBH is sufficiently massive. On timescales of 1 Myr or longer, the IMBH efficiently randomizes the eccentricities and orbital inclinations of the S-stars. Kozai oscillations are observed when the IMBH lies well outside the orbits of the stars. Perturbations from the IMBH can eject stars from the cluster, producing hypervelocity stars, and can also scatter stars into the SMBH; stars with high initial eccentricities are most likely to be affected in both cases. The distribution of S-star orbital elements is significantly altered from its currently observed form by IMBHs with masses greater than ∼10³M_☉ if the IMBH/SMBH semimajor axis lies in the range 3–10 mpc. We use these results to further constrain the allowed parameters of an IMBH/SMBH binary at the Galactic center.

We test the hypothesis that prompt gamma-ray burst (GRB) pulse emission starts simultaneously at all energies (the Pulse Start Conjecture). Our analysis, using a sample of BATSE bursts observed with four-channel, 64 ms data and performed using a pulse-fit model, generally supports this hypothesis for the Long GRB class, although a few discrepant pulses belong to bursts observed during times characterized by low signal-to-noise ratio, hidden pulses, and/or significant pulse overlap. The typical uncertainty in making this statement is <0.4 s for pulses in Long GRBs (and <0.2 s for 40% of the pulses) and perhaps <0.1 s for pulses in Short GRBs. When considered along with the E_pk decline found in GRB pulse evolution, this result implies that energy is injected at the beginning of each and every GRB pulse, and the subsequent spectral evolution, including the pulse peak intensity, represents radiated energy losses from this initial injection.

Four of nine exoplanets found by microlensing were detected by the resonant caustic, which represents the merging of the planetary and central caustics at the position when the projected separation of a host star and a bounded planet is s ∼ 1. One of the resonant caustic lensing events, OGLE-2005-BLG-169, was a caustic-crossing high-magnification event with A_max∼ 800 and the source star was much smaller than the caustic, nevertheless the perturbation was not obviously apparent on the light curve of the event. In this paper, we investigate the perturbation pattern of the resonant caustic to understand why the perturbations induced by the caustic do not leave strong traces on the light curves of high-magnification events despite a small source/caustic size ratio. From this study, we find that the regions with small magnification excess around the center of the resonant caustic are rather widely formed, and the event passing the small-excess region produces a high-magnification event with a weak perturbation that is small relative to the amplification caused by the star and thus does not noticeably appear on the light curve of the event. We also find that the positive excess of the inside edge of the resonant caustic and the negative excess inside the caustic become stronger and wider as q increases, and thus the resonant caustic-crossing high-magnification events with the weak perturbation occur in the range of q ⩽ 10⁻⁴. We determine the probability of the occurrence of events with the small excess || ⩽ 3% in high-magnification events induced by a resonant caustic. As a result, we find that for Earth-mass planets with a separation of ∼2.5 AU the resonant caustic high-magnification events with the weak perturbation can occur with a significant frequency.

We report the results of a 30 ks Chandra/ACIS-S observation of the isolated compact object (ICO) 1RXS J141256.0+792204 (Calvera). The X-ray spectrum is adequately described by an absorbed neutron star hydrogen atmosphere model with kT^∞_eff = 88.3 ± 0.8 eV and radiation radius R^∞/d = 4.1 ± 0.1 km kpc⁻¹. The best-fit blackbody spectrum yields parameters consistent with previous measurements; although the fit itself is not statistically acceptable, systematic uncertainties in the pile-up correction may contribute to this. We find marginal evidence for a narrow spectral feature in the X-ray spectrum between 0.3 and 1.0 keV. In one interpretation, we find evidence at 81% confidence for an absorption edge at E = 0.64^+0.08_-0.06 keV with equivalent width EW ≈ 70 eV; if this feature is real, it is reminiscent of features seen in the isolated neutron stars RX J1605.3+3249, RX J0720.4 − 3125, and 1RXS J130848.6+212708 (RBS 1223). In an alternative approach, we find evidence at 88% confidence for an unresolved emission line at energy E = 0.53 ± 0.02 keV, with equivalent width EW ≈ 28 eV; the interpretation of this feature, if real, is uncertain. We search for coherent pulsations up to the Nyquist frequency ν_Nyq = 1.13 Hz and set an upper limit of 8.0% rms on the strength of any such modulation. We derive an improved position for the source and set the most rigorous limits to date on any associated extended emission on arcsecond scales. Our analysis confirms the basic picture of Calvera as the first ICO in the ROSAT/Bright Source Catalog discovered in six years, the hottest such object known, and an intriguing target for multiwavelength study.

We present the spectra of 24 white dwarfs in the direction of the globular cluster Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs. Determining the spectral types of the stars in this sample, we find 24 type DA and 0 type DB (i.e., atmospheres dominated by hydrogen and helium, respectively). Assuming the ratio of DA/DB observed in the field with effective temperature between 15,000–25,000 K, i.e., 4.2:1, holds for the cluster environment, the chance of finding no DBs in our sample simply due to statistical fluctuations is only 6 × 10⁻³. The spectral types of the ∼100 white dwarfs previously identified in open clusters indicate that DB formation is strongly suppressed in that environment. Furthermore, all the ∼10 white dwarfs previously identified in other globular clusters are exclusively type DA. In the context of these two facts, this finding suggests that DB formation is suppressed in the cluster environment in general. Though no satisfactory explanation for this phenomenon exists, we discuss several possibilities.

Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main sequence today. Almost all of the stars born with more mass than 0.8 M_☉ have evolved to form the white dwarf cooling sequence of these systems, and the distribution and properties of these remnants uniquely holds clues related to the nature of the now evolved progenitor stars. With ultra-deep Hubble Space Telescope imaging observations, rich white dwarf populations of four nearby Milky Way globular clusters have recently been uncovered, and are found to extend impressive 5–8 mag in the faint-blue region of the Hertzsprung–Russell diagram. In this paper, we characterize the properties of these population II remnants by presenting the first direct mass measurements of individual white dwarfs near the tip of the cooling sequence in the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS multiobject spectroscopic observations, our results indicate that 0.8 M_☉ population II main-sequence stars evolving today form 0.53 ± 0.01 M_☉ white dwarfs. We discuss the implications of this result as it relates to our understanding of stellar structure and evolution of population II stars and for the age of the Galactic halo, as measured with white dwarf cooling theory.

Understanding the connection between the magnetic configurations of a coronal mass ejection (CME) and their counterpart in the interplanetary medium is very important in terms of space weather predictions. Our previous findings indicate that the orientation of a halo CME elongation may correspond to the orientation of the underlying flux rope. Here we further explore these preliminary results by comparing orientation angles of elongated LASCO CMEs, both full and partial halos, to the EUV Imaging Telescope post-eruption arcades (PEAs). By analyzing a sample of 100 events, we found that the overwhelming majority of CMEs are elongated in the direction of the axial field of PEAs. During their evolution, CMEs appear to rotate by about 10° for most of the events (70%) with about 30°–50° for some events, and the corresponding time profiles display regular and gradual changes. It seems that there is a slight preference for the CMEs to rotate toward the solar equator and heliospheric current sheet (59% of the cases). We suggest that the rotation of the ejecta may be due to the presence of a heliospheric magnetic field, and it could shed light on the problems related to connecting solar surface phenomena to their interplanetary counterparts.

Algol is a triple stellar system consisting of a close semidetached binary orbited by a third object. Due to the disputed spatial orientation of the close pair, the third body perturbation of this pair is a subject of much research. In this study, we determine the spatial orientation of the close pair orbital plane using the CHARA Array, a six-element optical/IR interferometer located on Mount Wilson, and state-of-the-art e-EVN interferometric techniques. We find that the longitude of the line of nodes for the close pair is Ω₁ = 48° ± 2° and the mutual inclination of the orbital planes of the close and the wide pairs is 95° ± 3°. This latter value differs by 5° from the formerly known 100°, which would imply a very fast inclination variation of the system, not borne out by the photometric observations. We also investigated the dynamics of the system with numerical integration of the equations of motions using our result as an initial condition. We found large variations in the inclination of the close pair (its amplitude ∼170°) with a period of about 20 millennia. This result is in good agreement with the photometrically observed change of amplitude in Algol's primary minimum.

Many small molecules including carbon clusters emit blackbody radiation in the visible spectrum when their internal temperature, T, is raised above 2000 K by photoabsorption. Blackbody emission is known to be the dominant cooling mechanism for small dehydrogenated carbon molecules for 1500 < T < 3000 K. The condition that T > 2000 K would be met by interstellar molecules containing ≤28 carbon atoms, heated by energetic photons from the interstellar radiation field. It is shown here that thermal emission will augment photoluminescent emission in extended red emission (ERE) sources when the UV radiation field is enhanced. In particular, this mechanism provides a simple explanation for observations that show that only stars with T_eff > 7000 K excite the ERE. The observation by Witt et al. that photons with energies >10.5 eV are required for the onset of ERE emission can then be interpreted as the condition for the initiation of thermal emission at visible wavelengths. These observational requirements have been combined with laboratory and theoretical data to constrain the emitters of the ERE to dehydrogenated carbon molecules, C_N with 20 ≤ N ≤ 28 atoms. The composition and structure of these molecules is discussed and IR band energies for several possible C_N species are provided. These molecules are stable against photodissociation in the interstellar radiation field. It is also shown that dimers of these molecules, (C_N)₂, may be the species that give rise to the near-infrared continuum first detected by Sellgren. A new effect that might be significant under interstellar conditions involving unimolecular rearrangement reactions in thermally excited molecules is also discussed.

We present the results of X-ray spectral analysis of 22 active galactic nuclei (AGNs) with a small scattering fraction selected from the Second XMM-Newton Serendipitous Source Catalogue using hardness ratios. They are candidates of buried AGNs, since a scattering fraction, which is a fraction of scattered emission by the circumnuclear photoionized gas with respect to direct emission, can be used to estimate the size of the opening part of an obscuring torus. Their X-ray spectra are modeled by a combination of a power law with a photon index of 1.5–2 absorbed by a column density of ∼10^23–24 cm⁻², an unabsorbed power law, narrow Gaussian lines, and some additional soft components. We find that scattering fractions of 20 among 22 objects are less than a typical value (∼3%) for Seyfert 2s observed so far. In particular, those of eight objects are smaller than 0.5%, which are in the range for buried AGNs found in recent hard X-ray surveys. Moreover, [O iii] λ5007 luminosities at given X-ray luminosities for some objects are smaller than those for Seyfert 2s previously known. This fact could be interpreted as a smaller size of optical narrow emission-line regions produced in the opening direction of the obscuring torus. These results indicate that they are strong candidates for the AGN buried in a very geometrically thick torus.

We have carried out a survey of the dense clumps associated with 14 embedded clusters in the C¹⁸O (J = 1–0) line emission with the Nobeyama 45 m telescope in order to understand the formation and evolution of stellar clusters in dense clumps of molecular clouds. We have selected these clusters at distances from 0.3 to 2.1 kpc and have mapped about 6' × 6'–10' × 10' regions (corresponding to 3.8 pc × 3.8 pc at 2.1 kpc) for all the clumps with 22'' resolution (corresponding to Jeans length at 2.1 kpc). We have obtained dense clumps with radii of 0.40–1.6 pc, masses of 150–4600 M_☉, and velocity widths in FWHM of 1.4–3.3 km s⁻¹. Most of the clumps are found to be approximately in virial equilibrium, which implies that C¹⁸O gas represents parental dense clumps for cluster formation. From the spatial relation between the distributions of clumps and clusters, we classified C¹⁸O clumps into three types (Type A, B, and C). Type A clumps have emission distributions with a single peak at the stellar clusters and higher brightness contrast than that of other target sources. Type B clumps have double or triple peaks, which are associated with the cluster, and moderately high brightness contrast structure. Type C clumps also have multiple peaks, although they are not associated with the cluster, and low brightness contrast structure. We suggest that our classification represents an evolutionary trend of cluster-forming dense clumps because dense gas in molecular clouds is expected to be converted into stellar constituents, or dispersed by stellar activities. Moreover, although there is a scatter, we found a tendency that the star formation efficiencies of the dense clumps increase from Type A to Type C, which also supports our scenario.

We investigate two potential mechanisms that will produce X-ray and γ-ray flashes from Type Ia supernovae (SN-Ia). The first mechanism is the breakout of the thermonuclear burning front as it reaches the surface of the white dwarf (WD). The second mechanism is the interaction of the rapidly expanding envelope with material within an accretion disk in the progenitor system. Our study is based on the delayed detonation scenario because this can account for the majority of light curves, spectra, and statistical properties of "Branch-normal" SN-Ia. Based on detailed radiation-hydro calculations which include nuclear networks, we find that both mechanisms produce brief flashes of high-energy radiation with peak luminosities of 10⁴⁸–10⁵⁰ erg s⁻¹. The breakout from the WD surface produces flashes with a rapid exponential decay by 3–4 orders of magnitude on timescales of a few tenths of a second and with most of the radiation in the X-ray and soft γ-ray range. The shocks produced in gases in and around the binary will produce flashes with a characteristic duration of a few seconds with most of the radiation coming out as X-rays and γ-rays. In both mechanisms, we expect a fast rise and slow decline and, after the peak, an evolution from hard to softer radiation due to adiabatic expansion. In many cases, flashes from both mechanisms will be superposed. The X- and γ-ray visibility of an SN-Ia will depend strongly on self-absorption within the progenitor system, specifically on the properties of the accretion disk and its orientation toward the observer. Such X-ray and γ-ray flashes could be detected as triggered events by gamma-ray burst (GRB) detectors on satellites, with events in current GRB catalogs. We have searched through the GRB catalogs (for the BATSE, HETE, and Swift experiments) for GRBs that occur at the extrapolated time of explosion and in the correct direction for known Type Ia supernovae with radial velocity of less than 3000 km s⁻¹. For the Burst and Transient Source Experiment (BATSE) about 12.9 ± 3.6 nearby SNe Ia should have been detected, but only 0.8 ± 0.7 non-coincidental matches have been found. With the High Energy Transient Explorer (HETE) and Swift satellites, we expect to see 5.6 ± 1.3 SN-Ia flashes from known nearby SNe Ia but, yet, no SN-Ia flashes were detected. With the trigger thresholds for these experiments and the upper limits on the SN-Ia distances, we show that the bolometric peak luminosity of SN-Ia flashes must be less ∼10⁴⁶ erg s⁻¹. Our observational limit is several orders-of-magnitude smaller than the peak luminosities predicted for both the early flashes. We attribute this difference to the absorption of the X- and γ-rays by the accretion disk of large-scale height or common envelope that would be smothering the WD.

We report results from a 2007 Suzaku observation of the Seyfert 1 AGN NGC 4593. The narrow Fe Kα emission line has a FWHM width ∼ 4000 km s⁻¹, indicating emission from ≳ 5000 R_g. There is no evidence for a relativistically broadened Fe K line, consistent with the presence of a radiatively efficient outer disk which is truncated or transitions to an interior radiatively inefficient flow. The Suzaku observation caught the source in a low-flux state; comparison to a 2002 XMM-Newton observation indicates that the hard X-ray flux decreased by 3.6, while the Fe Kα line intensity and width σ each roughly halved. Two model-dependent explanations for the changes in Fe Kα line profile are explored. In one, the Fe Kα line width has decreased from ∼10,000 to ∼4000 km s⁻¹ from 2002 to 2007, suggesting that the thin disk truncation/transition radius has increased from 1000–2000 to ≳5000 R_g. However, there are indications from other compact accreting systems that such truncation radii tend to be associated only with accretion rates relative to Eddington much lower than that of NGC 4593. In the second model, the line profile in the XMM-Newton observation consists of a time-invariant narrow component plus a broad component originating from the inner part of the truncated disk (∼300 R_g) which has responded to the drop in continuum flux. The Compton reflection component strength R is ∼ 1.1, consistent with the measured Fe Kα line total equivalent width with an Fe abundance 1.7 times the solar value. The modest soft excess, modeled well by either thermal bremsstrahlung emission or by Comptonization of soft seed photons in an optical thin plasma, has fallen by a factor of ∼20 from 2002 to 2007, ruling out emission from a region 5 lt-yr in size.

Using the High Dispersion Spectrograph (HDS) at the Subaru Telescope, we secured the high-resolution line spectra in the 3600–7500 Å wavelength range of the Galactic halo planetary nebula DdDm 1. We also analyzed the Hubble Space Telescope Faint Object Spectrograph data in the 1200–6730 Å wavelength range. The diagnostic results indicate the electron temperatures of T∼ 11,000–14,000 K and the electron number densities of N∼ 2000–10,500 cm⁻³. In spite of high gaseous temperatures, we have not detected high excitation lines, e.g., He ii. We derived abundance based on the ionic concentration of permitted and forbidden lines and the photoionization model. A comparison of the ionic concentrations from forbidden lines to recombination lines shows the abundance discrepancy between them. We tested various possibilities, e.g., temperature fluctuation and high-density blob components, to explain the discrepancy. The high-density components or density fluctuation might be partly responsible for the discrepancy. DdDm 1 shows a low carbon abundance that corresponds to metal-poor stars, [Fe/H] ⩽−1. Assuming a distance of 10 kpc to DdDm 1, theoretical models suggest that the central star has T_eff≃ 39,000 K and L≃ 2000–3000 L_☉. The relatively high gas temperatures appear to be caused by very low heavy elemental abundances or insufficient coolants in the shell gas. Its progenitor, born in an extremely carbon-poor environment as an initial mass of about 0.9 M_☉, had probably experienced only the first dredge-up.

We present three-dimensional models of dust distribution around β Pictoris that produce the best fits to the Hubble Space Telescope/Advanced Camera for Surveys' images obtained by Golimowski and coworkers. We allow for the presence of either one or two separate axisymmetric dust disks. The density models are analytical, radial two power laws joined smoothly at a crossover radius with density exponentially decreasing away from the midplane of the disks. Two-disk models match the data best, yielding a reduced χ² of ∼1.2. Our two-disk model reproduces many of the asymmetries reported in the literature and suggests that it is the secondary (tilted) disk which is largely responsible for them. Our model suggests that the secondary disk is not constrained to the inner regions of the system (extending out to at least 250 AU) and that it has a slightly larger total area of dust than the primary, as a result of slower falloff of density with radius and height. This surprising result raises many questions about the origin and dynamics of such a pair of disks. The disks overlap, but can coexist owing to their low optical depths and therefore long mean collision times. We find that the two disks have dust replenishment times on the order of 10⁴ yr at ∼100 AU, hinting at the presence of planetesimals that are responsible for the production of second generation dust. A plausible conjecture, which needs to be confirmed by physical modeling of the collisional dynamics of bodies in the disks, is that the two observed disks are derived from underlying planetesimal disks; such disks would be anchored by the gravitational influence of planets located at less than 70 AU from β Pic that are themselves in slightly inclined orbits.

We have designed and constructed a second-generation version of the dispersed Fourier transform spectrograph, or dFTS. This instrument combines a spectral interferometer with a dispersive spectrograph to provide high-accuracy, high-resolution optical spectra of stellar targets. The new version, dFTS2, is based upon the design of our prototype, with several modifications to improve the system throughput and performance. We deployed dFTS2 to the Steward Observatory 2.3 m Bok Telescope from 2007 June to 2008 June, and undertook an observing program on spectroscopic binary stars, with the goal of constraining the velocity amplitude K of the binary orbits with 0.1% accuracy, a significant improvement over most of the orbits reported in the literature. We present results for radial velocity reference stars and orbit solutions for single-lined spectroscopic binaries.

Ultraviolet and hard X-ray (HXR) emissions in solar flares provide observational signatures of the interaction of flare-accelerated particles with the chromospheric plasma. Earlier studies have shown clear evidence of temporal and spatial relationships between UV and HXR emission, suggesting a common physical origin. However, more recent spatially resolved case studies suggest significant variations in the spatial distributions of the emission signatures, implying that the large-scale magnetic topology of the flaring region must play a crucial role in the spatial and temporal development of the localized UV and HXR emission. We present here an analysis of spatially resolved HXR emission and localized UV emission sources from 11 M and X class flares with observations from RHESSI and high-cadence 1600 Å observations from TRACE. Within each flare we address the overall temporal development of individual UV sources and relate them to associated impulsive bursts within the HXR flare profile. We find, for these large flares, that in the initial impulsive bursts of flare activity, the majority of the temporally correlated emission evolves in a series of localized co-spatial sources along the UV ribbons consistent with previous two-dimensional reconnection pictures. However, observations of impulses late in flares, show significant departures from the traditional co-spatial/co-temporal picture. The new results include extended UV ribbons with no corresponding HXR emission and marked spatial separations between temporally correlated sources of UV and HXR emission. In seven of the multi-burst events, we observe the development of independent sets of UV and HXR sources corresponding to the individual impulses seen in the temporal profile. The observed separations and the spatial development of co-temporal emission in multi-burst events emphasize the importance of a complex and time varying magnetic topology in shaping the observed emission distributions in both wavelengths. In four of the events, we observe late developing UV sources which show no relationship with the HXR emission. In these events, the emission sources show a strong relationship with lower energy, more spatially extended X-ray emission believed to be of thermal origin. This suggests that, in the later phase of these complex flares, emission from thermal processes comes to dominate non-thermal processes in the production of the UV emission.

The majority of active galactic nuclei (AGNs) suffer from significant obscuration by surrounding dust and gas. The penetrating power and sensitivity of hard X-ray observations allow obscured AGNs to be probed out to high redshifts. However, X-ray surveys in the 2–10 keV band will miss the most heavily obscured AGNs in which the absorbing column density exceeds ∼10²⁴ cm⁻² (the Compton-thick AGN). It is, therefore, vital to know the fraction of AGNs that are missed in such X-ray surveys and to determine if these AGNs represent some distinct population in terms of the fundamental properties of AGNs and/or their host galaxies. In this paper, we present the analysis of XMM-Newton X-ray data for a complete sample of 17 low-redshift Type 2 Seyfert galaxies chosen from the Sloan Digital Sky Survey based solely on the high observed flux of the [O iii]λ5007 emission line. This line is formed in the narrow-line region hundreds of parsecs away from the central engine. Thus, unlike the X-ray emission, it is not affected by obscuration due to the torus surrounding the black hole. It therefore provides a useful isotropic indicator of the AGN luminosity. As additional indicators of the intrinsic AGN luminosity, we use the Spitzer Space Telescope to measure the luminosities of the mid-infrared continuum and the [O iv] 25.89 μm narrow emission line. We then use the ratio of the 2–10 keV X-ray luminosity to the [O iii], [O iv], and mid-infrared luminosities to assess the amount of X-ray obscuration and to distinguish between Compton-thick and Compton-thin objects. The various diagnostics of AGN luminosity with heavily obscured hard X-ray emission are in broad agreement. We find that the majority of the sources suffer significant amounts of obscuration: the observed 2–10 keV emission is depressed by more than an order of magnitude in 11 of the 17 cases (as expected for Compton-thick sources). Thus, surveys in the rest-frame 2–10 keV band will be significantly incomplete for obscured AGNs. We find a strong inverse correlation between the ratio of the 2–10 keV X-ray and [O iii] (or [O iv] or mid-IR) fluxes and the equivalent width of the 6.4 keV Fe Kα line. This demonstrates that the weak hard X-ray continuum emission is due to obscuration (rather than due to intrinsically weak emission). In several cases, the large amount of obscuration is not consistent with the values of absorbing column density derived from simple spectral fits to the data. We run simulations of a more physically realistic model with partial covering of the X-ray source plus Compton scattering, and show that such models are consistent with the data. We show that the distribution of obscuration in the 2–10 keV band in our sample is similar to what is seen in samples selected in the Swift BAT energy band (14–195 keV). This implies that the BAT surveys do recover a significant fraction of the local population of Compton-thick AGNs. Finally, we find no relationship between the amount of X-ray obscuration and the other properties of the AGN and its host galaxy. Hence, Compton-thick and Compton-thin sources do not seem to trace distinct populations.

On 2009 February 13, a coronal wave—CME—dimming event was observed in quadrature by the Solar Terrestrial Relations Observatory (STEREO) spacecraft. We analyze this event using a three-dimensional, global magnetohydrodynamic model for the solar corona. The numerical simulation is driven and constrained by the observations, and indicates where magnetic reconnection occurs between the expanding CME core and surrounding environment. We focus primarily on the lower corona, extending out to 3 R_☉; this range allows simultaneous comparison with both EUVI and COR1 data. Our simulation produces a diffuse coronal bright front remarkably similar to that observed by STEREO/EUVI at 195 Å. It is made up of two components, and is the result of a combination of both wave and non-wave mechanisms. The CME becomes large-scale quite low (< 200 Mm) in the corona. It is not, however, an inherently large-scale event; rather, the expansion is facilitated by magnetic reconnection between the expanding CME core and the surrounding magnetic environment. In support of this, we also find numerous secondary dimmings, many far from the initial CME source region. Relating such dimmings to reconnecting field lines within the simulation provides further evidence that CME expansion leads to the "opening" of coronal field lines on a global scale. Throughout the CME expansion, the coronal wave maps directly to the CME footprint. Our results suggest that the ongoing debate over the "true" nature of diffuse coronal waves may be mischaracterized. It appears that both wave and non-wave models are required to explain the observations and understand the complex nature of these events.

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting cataclysmic variable (CV) dwarf novae (DN) systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar, and black hole systems. We find that spinning, tilted CV DN systems cannot be described by a precessing ring or by a precessing rigid disk. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. In agreement with the observations and numerical simulations by others, we find that our numerically simulated CV DN accretion disks retrogradely precess as a unit. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main-sequence secondaries. Our results suggest that a major source to retrograde precession is tidal torques like that by the Moon and the Sun on the Earth. In addition, these tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if accretion disks are present or not. Our results suggest that the accretion disk's geometric shape directly affects the disk's precession rate.

We investigate the star formation history of the universe using FIREWORKS, a multiwavelength survey of the Chandra Deep Field South. We study the evolution of the specific star formation rate (sSFR) with redshift in different mass bins from z = 0 to z ∼ 3. We find that the sSFR increases with redshift for all masses. The logarithmic increase of the sSFR with redshift is nearly independent of mass, but this cannot yet be verified at the lowest-mass bins at z>0.8, due to incompleteness. We convert the sSFRs to a dimensionless growth rate to facilitate a comparison with a semianalytic galaxy formation model that was implemented on the Millennium Simulation. The model predicts that the growth rates and sSFRs increase similarly with redshift for all masses, consistent with the observations. However, we find that for all masses, the inferred observed growth rates increase more rapidly with redshift than the model predictions. We discuss several possible causes for this discrepancy, ranging from field-to-field variance, conversions to SFR, and shape of the initial mass function. We find that none of these can solve the discrepancy completely. We conclude that the models need to be adapted to produce the steep increase in growth rate between redshift z = 0 and z = 1.

A Chandra observation of the X-ray bright group NGC 5044 shows that the X-ray emitting gas has been strongly perturbed by recent outbursts from the central active galactic nucleus (AGN) and also by motion of the central dominant galaxy relative to the group gas. The NGC 5044 group hosts many small radio-quiet cavities with a nearly isotropic distribution, cool filaments, a semi-circular cold front, and a two-armed spiral shaped feature of cool gas. A Giant Metrewave Radio Telescope (GMRT) observation of NGC 5044 at 610 MHz shows the presence of extended radio emission with a "torus-shaped" morphology. The largest X-ray filament appears to thread the radio torus, suggesting that the lower entropy gas within the filament is material being uplifted from the center of the group. The radio emission at 235 MHz is much more extended than the emission at 610 MHz, with little overlap between the two frequencies. One component of the 235 MHz emission passes through the largest X-ray cavity and is then deflected just behind the cold front. A second detached radio lobe is also detected at 235 MHz beyond the cold front. All of the smaller X-ray cavities in the center of NGC 5044 are undetected in the GMRT observations. Since the smaller bubbles are probably no longer momentum driven by the central AGN, their motion will be affected by the group "weather" as they buoyantly rise outward. Hence, most of the enthalpy within the smaller bubbles will likely be deposited near the group center and isotropized by the group weather. The total mechanical power of the smaller radio quiet cavities is P_c = 9.2 × 10⁴¹ erg s⁻¹ which is sufficient to suppress about one-half of the total radiative cooling within the central 10 kpc. This is consistent with the presence of Hα emission within this region which shows that at least some of the gas is able to cool. The mechanical heating power of the larger southern cavity, located between 10 and 20 kpc, is six times greater than the combined mechanical power of the smaller radio-quiet cavities and could suppress all radiative cooling within the central 25 kpc if the energy were deposited and isotropized within this region. Within the central 20 kpc, emission from low-mass X-ray binaries (LMXBs) is a significant component of the X-ray emission above 2 keV. The presence of hard X-ray emission from unresolved LMXBs makes it difficult to place strong constraints on the amount of shock heated gas within the X-ray cavities.

We present a rest-frame ultraviolet analysis of ∼120 z ∼ 3.1 Lyman Alpha Emitters (LAEs) in the Extended Chandra Deep Field South. Using Hubble Space Telescope (HST) images taken as part of the Galaxy Evolution From Morphology and SEDS (GEMS) survey, Great Observatories Origins Deep Survey (GOODS), and Hubble Ultradeep Field surveys, we analyze the sizes of LAEs, as well as the spatial distribution of their components, which are defined as distinct clumps of UV-continuum emission. We set an upper limit of ∼1 kpc (∼01) on the rms offset between the centroids of the continuum and Lyα emission. The SFRs of LAE components inferred from the rest-frame ultraviolet continuum range from ∼0.1 M_☉ yr⁻¹ to ∼5 M_☉ yr⁻¹. A subsample of LAEs with coverage in multiple surveys (at different imaging depths) suggests that one needs a signal-to-noise ratio, S/N ≳30, in order to make a robust estimate of the half-light radius of an LAE system. The majority of LAEs have observed half-light radii ≲2 kpc, and LAE components typically have observed half-light radii ≲1.5 kpc (≲020). Although only ∼50% of the detected LAE components are resolved at GOODS depth, the brightest (V ≲ 26.3) are all resolved in both GOODS and GEMS. Since we find little evidence for a correlation between the rest-UV sizes and magnitudes of LAEs, the majority should be resolved in a deeper survey at the ∼005 angular resolution of the HST. Most of the multi-component LAEs identified in shallow frames become connected in deeper images, suggesting that the majority of the rest-UV "clumps" are individual star-forming regions within a single system.

The timescale for star formation, a measure of how quickly neutral gas is being converted to stars, is considerably longer than typical dynamical timescales associated with a galactic disk. For purposes of modeling galaxy evolution, however, it would be extremely attractive if the star formation timescale was proportional to an easily derived dynamical timescale. We compare estimates of the star formation timescale within nearby galaxies, based on the work of Leroy et al. and existing BIMA Survey of Nearby Galaxies CO data, with three simple forms of the dynamical time: the orbital time; the free-fall time at the midplane density; and the disk Jeans time (the growth time for gravitational instabilities in a disk). When taking into account the gravity of the stellar disk in an approximate way, all three timescales show correlations with the star formation timescale, though none of the correlations can be accurately described as linear. Systematic errors in estimating appropriate gas masses and the stellar velocity dispersion may obscure an underlying correlation, but we focus instead on a model where the timescale for H₂ formation from H i is decoupled from the timescale for star formation from H₂. The Jeans time correlates well with the first of these timescales, but the relationship is still non-linear and requires a characteristic giant molecular cloud lifetime that increases toward galaxy centers.

It was suggested by several authors that hypothetical primordial black holes (PBHs) may contribute to the dark matter (DM) in our Galaxy. There are strong constraints based on the Hawking evaporation that practically exclude PBHs with masses m_pbh ∼ 10¹⁵to10¹⁶ g and smaller as significant contributors to the Galactic DM. Similarly, PBHs with masses greater than about 10²⁶ g are practically excluded by the gravitational lensing observation. The mass range between 10¹⁶ g <m_pbh < 10²⁶ g is unconstrained. In this paper, we examine possible observational signatures in the unexplored mass range, investigating hypothetical collisions of PBHs with main-sequence stars, red giants, white dwarfs, and neutron stars in our Galaxy. This has previously been discussed as possibly leading to an observable photon eruption due to shock production during the encounter. We find that such collisions are either too rare to be observed (if the PBH masses are typically larger than about 10²⁰ g), or produce too little power to be detected (if the masses are smaller than about 10²⁰ g).

Analyses of the cosmic microwave background (CMB) radiation maps made by the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies not predicted by the standard inflationary cosmology. In particular, the power of the quadrupole moment of the CMB fluctuations is remarkably low, and the quadrupole and octopole moments are aligned mutually and with the geometry of the solar system. It has been suggested in the literature that microwave sky pollution by an unidentified dust cloud in the vicinity of the solar system may be the cause for these anomalies. In this paper, we simulate the thermal emission by clouds of spherical homogeneous particles of several materials. Spectral constraints from the WMAP multi-wavelength data and earlier infrared observations on the hypothetical dust cloud are used to determine the dust cloud's physical characteristics. In order for its emissivity to demonstrate a flat, CMB-like wavelength dependence over the WMAP wavelengths (3 through 14 mm), and to be invisible in the infrared light, its particles must be macroscopic. Silicate spheres of several millimeters in size and carbonaceous particles an order of magnitude smaller will suffice. According to our estimates of the abundance of such particles in the zodiacal cloud and trans-Neptunian belt, yielding the optical depths of the order of 10⁻⁷ for each cloud, the solar system dust can well contribute 10 μK (within an order of magnitude) in the microwaves. This is not only intriguingly close to the magnitude of the anomalies (about 30 μK), but also alarmingly above the presently believed magnitude of systematic biases of the WMAP results (below 5 μK) and, to an even greater degree, of the future missions with higher sensitivities, e.g., Planck.

Main-sequence stars earlier than spectral-type ∼F6 or so are expected to rotate rapidly due to their radiative exteriors. This rapid rotation leads to an oblate stellar figure. It also induces the photosphere to be hotter (by up to several thousand kelvin) at the pole than at the equator as a result of a process called gravity darkening that was first predicted by von Zeipel. Transits of extrasolar planets across such a non-uniform, oblate disk yield unusual and distinctive lightcurves that can be used to determine the relative alignment of the stellar rotation pole and the planet orbit normal. This spin–orbit alignment can be used to constrain models of planet formation and evolution. Orderly planet formation and migration within a disk that is coplanar with the stellar equator will result in spin–orbit alignment. More violent planet–planet scattering events should yield spin–orbit misaligned planets. Rossiter–McLaughlin measurements of transits of lower-mass stars show that some planets are spin–orbit aligned, and some are not. Since Rossiter–McLaughlin measurements are difficult around rapid rotators, lightcurve photometry may be the best way to determine the spin–orbit alignment of planets around massive stars. The Kepler mission will monitor ∼10⁴ of these stars within its sample. The lightcurves of any detected planets will allow us to probe the planet formation process around high-mass stars for the first time.

Binary evolution predicts a population of helium core (M < 0.5 M_☉) white dwarfs (WDs) that are slowly accreting hydrogen-rich material from low-mass main-sequence or brown dwarf donors with orbital periods less than 4 hr. Four binaries are presently known in the Milky Way that will reach such a mass-transferring state in a few Gyr. Despite these predictions and observations of progenitor binaries, there are still no secure cases of helium core WDs among the mass-transferring cataclysmic variables. This led us to calculate the fate of He WDs once accretion begins at a rate $\dot{M}<10^{-10} \ M_\odot \ {\rm yr}^{-1}$ set by angular momentum losses. We show here that the cold He core temperatures (T_c < 10⁷ K) and low $\dot{M}$ result in ∼10⁻³ M_☉ of accumulated H-rich material at the onset of the thermonuclear runaway. Shara and collaborators noted that these large accumulated masses may lead to exceptionally long classical nova (CN) events. For a typical donor star of 0.2 M_☉, such binaries will only yield a few hundred CNe, making these events rare among all CNe. We calculate the reheating of the accreting WD, allowing a comparison to the measured WD effective temperatures in quiescent dwarf novae and raising the possibility that WD seismology may be the best way to confirm the presence of a He WD. We also find that a very long (>1000 yr) stable burning phase occurs after the CN outburst, potentially explaining enigmatic short orbital period supersoft sources like RX J0537–7034 (P_orb = 3.5 hr) and 1E 0035.4–7230 (P_orb = 4.1 hr).

We present the star formation history (SFH) and its variations with galactocentric distance for the Local Group dwarf galaxy of Phoenix. They have been derived from a (F555W, F814W) color–magnitude diagram obtained from WFPC2@HST data, which reaches the oldest main-sequence turnoffs. The IAC-star and IAC-pop codes and the MinnIAC suite have been used to obtain the star formation rate as a function of time and metallicity, ψ(t, z). We find that Phoenix has had ongoing but gradually decreasing star formation over nearly a Hubble time. The highest level of star formation occurred from the formation of the galaxy till 10.5 Gyr ago, when 50% of the total star formation had already taken place. From that moment, star formation continues at a significant level until 6 Gyr ago (an additional 35% of the stars are formed in this time interval), and at a very low level till the present time. The chemical enrichment law shows a trend of slowly increasing metallicity as a function of time until 6–8 Gyr ago, when metallicity starts to increase steeply to the current value. We have paid particular attention to the study of the variations of the SFH as a function of radius. Young stars are found in the inner region of the galaxy only, but intermediate-age and old stars can be found at all galactocentric distances. The distribution of mass density in alive stars and its evolution with time has been studied. This study shows that star formation started at all galactocentric distances in Phoenix at an early epoch. If stars form in situ in Phoenix, the star formation onset took place all over the galaxy (up to a distance of about 400 pc from the center), but preferentially out of center regions. After that, our results are compatible with a scenario in which the star formation region envelope slowly shrinks as time goes on, possibly as a natural result of pressure support reduction as gas supply diminishes. As a consequence, the star formation stopped first (about 7–8 Gyr ago) in outer regions and the scale length of the stellar mass density distribution decreased with time. Finally, no traces of a true, old halo are apparent in Phoenix either in its stellar age distribution or in the stellar mass density distribution, at least out to 0.5 kpc (about 2.5 scale length) from the center.

We present the first 350 μm polarization measurement for the disk of the T Tauri star (TTS) DG Tau. The data were obtained using the SHARP polarimeter at the Caltech Submillimeter Observatory. We measured normalized Stokes parameters q= −0.0086 ± 0.0060 and u = −0.0012 ± 0.0061, which gives a 2σ upper limit for the percent polarization of 1.7%. We obtain information about the polarization spectrum by comparing our 350 μm measurement with an 850 μm polarization detection previously published for this source. Comparing the two measurements in Stokes space (not in percent polarization) shows that the two data points are not consistent, i.e., either the degree of polarization or the angle of polarization (or both) must change significantly as one moves from 850 μm to 350 μm. This conclusion concerning the polarization spectrum disagrees with the predictions of a recent model for TTS disk polarization. We show that this discrepancy can be explained by optical depth effects. Specifically, we demonstrate that if one were to add more mass to the model disk, one would expect to obtain a model polarization spectrum in which the polarization degree falls sharply with increasing frequency, consistent with the observations at the two wavelengths. We suggest that multiwavelength polarimetry of TTS disk emission may provide a promising method for probing the opacity of TTS disks.

We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H ii regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H ii region had a detection of the temperature sensitive [O iii] λ4363 line, allowing a "direct" determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies, and the observed oxygen abundances are typically in agreement with the well-known metallicity–luminosity relation. However, three candidate "tidal dwarf" galaxies lie well off this relation: UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sight as the M81 tidal debris field. We propose that these H ii regions formed from previously enriched gas which was stripped from nearby massive galaxies (e.g., NGC 3077 and M81) during a recent tidal interaction.

We investigate the quality of associations of astronomical sources from multi-wavelength observations using simulated detections that are realistic in terms of their astrometric accuracy, small-scale clustering properties and selection functions. We present a general method to build such mock catalogs for studying associations, and compare the statistics of cross-identifications based on angular separation and Bayesian probability criteria. In particular, we focus on the highly relevant problem of cross-correlating the ultraviolet Galaxy Evolution Explorer (GALEX) and optical Sloan Digital Sky Survey (SDSS) surveys. Using refined simulations of the relevant catalogs, we find that the probability thresholds yield lower contamination of false associations, and are more efficient than angular separation. Our study presents a set of recommended criteria to construct reliable cross-match catalogs between SDSS and GALEX with minimal artifacts.

We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the Infrared Array Camera and Multiband Imaging Photometer cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the red giant branch (RGB) that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the RGB. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0^+2.0_−1.2 × 10⁻⁹ M_☉ yr^-1, corresponding to a gas mass-loss rate of 8.6^+5.6_−3.4 × 10⁻⁶ M_☉ yr^-1, assuming [Fe/H] =−1.16. This mass loss is in addition to any dustless mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in ω Centauri.

We present the discovery of two new dwarf galaxies, Andromeda XXI and Andromeda XXII, located in the surroundings of the Andromeda and Triangulum galaxies (M31 and M33). These discoveries stem from the first year data of the Pan-Andromeda Archaeological Survey, a photometric survey of the M31/M33 group conducted with the Megaprime/MegaCam Wide-Field Camera mounted on the Canada–France–Hawaii Telescope. Both satellites appear as spatial overdensities of stars which, when plotted in a color-magnitude diagram, follow metal-poor, [Fe/H] = −1.8, red giant branches at the distance of M31/M33. Andromeda XXI is a moderately bright dwarf galaxy (M_V = −9.9 ± 0.6), albeit with low surface brightness, emphasizing again that many relatively luminous M31 satellites still remain to be discovered. It is also a large satellite, with a half-light radius close to 1 kpc, making it the fourth largest Local Group dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda II, and Sagittarius around the Milky Way, and supports the trend that M31 satellites are larger than their Milky Way counterparts. Andromeda XXII is much fainter (M_V = −6.5 ± 0.8) and lies a lot closer in projection to M33 than it does to M31 (42 versus 224 kpc), suggesting that it could be the first Triangulum satellite to be discovered. Although this is a very exciting possibility in the context of a past interaction of M33 with M31 and the fate of its satellite system, a confirmation will have to await a good distance estimate to confirm its physical proximity to M33. Along with the dwarf galaxies found in previous surveys of the M31 surroundings, these two new satellites bring the number of dwarf spheroidal galaxies in this region to 20.

We present starburst models for far-infrared/sub-millimeter/millimeter line emission of molecular and atomic gas in an evolving starburst region, which is treated as an ensemble of noninteracting hot bubbles that drive spherical shells of swept-up gas into a surrounding uniform gas medium. These bubbles and shells are driven by stellar winds and supernovae within massive star clusters formed during an instantaneous starburst. The underlying stellar radiation from the evolving clusters affects the properties and structure of photodissociation regions (PDRs) in the shells, and hence the spectral energy distributions (SEDs) of the molecular and atomic line emission from these swept-up shells and the associated parent giant molecular clouds contain a signature of the stage of evolution of the starburst. The physical and chemical properties of the shells and their structure are computed using a simple, well-known similarity solution for the shell expansion, a stellar population synthesis code, and a time-dependent PDR chemistry model. The SEDs for several molecular and atomic lines (¹²CO and its isotope ¹³CO, HCN, HCO⁺, C, O, and C⁺) are computed using a nonlocal thermodynamic equilibrium line radiative transfer model. By comparing our models with the available observed data of nearby infrared bright galaxies, especially M 82, we constrain the models and in the case of M 82, we provide estimates for the ages (5–6 Myr, 10 Myr) of recent starburst activity. We also derive a total H₂ gas mass of ∼(2–3.4) × 10⁸ M_☉ for the observed regions of the central 1 kpc starburst disk of M 82.

Twenty P-branch transitions of ¹²C₂H₂ have been measured in the 0.8–1.6 THz region of its bending vibrational difference band. The accuracy of these measurements is estimated to be 100 kHz. The ¹²C₂H₂ molecules were generated under room temperature by passing 150 mTorr H₂O vapor through calcium carbide (CaC₂) powder. The observed transitions were modeled together with prior far-infrared data involving the bending levels with $\sum\nolimits_t {V_t (t = 4,5) \le 2}$. Frequency predictions of ¹²C₂H₂ in the terahertz region have been greatly improved by adding the first data of "microwave" precision. The new measurements and predictions reported here will facilitate the analyses of astronomical observations by the high spectral resolution telescopes such as Herschel, SOFIA, and ALMA.

Amorphization of crystalline olivine to glass with a pyroxene composition is well known from high-energy irradiation experiments. This report is on the first natural occurrence of this process preserved in a chondritic aggregate interplanetary dust particle. The Fe-rich olivine grain textures and compositions and the glass grain compositions delineate this transformation that yielded glass with Fe-rich pyroxene compositions. The average glass composition, (Mg, Fe)₃Si₂O₇, is a serpentine-dehydroxylate with O/Si = 3.56 ± 0.25, (Mg+Fe)/Si = 1.53 ± 0.24, and Mg/(Mg+Fe) = 0.74 ± 0.1. These measured atomic ratios match the ratios that have been proposed for amorphous interstellar silicate grains very well, albeit the measured Mg/(Mg+Fe) ratio is lower than was proposed for amorphous interstellar silicate grains, Mg/(Mg+Fe) > 0.9.

The nearby isolated neutron stars (INSs) are a group of seven relatively slowly rotating neutron stars that show thermal X-ray spectra, most with broad absorption features. They are interesting both because they may allow one to determine fundamental neutron-star properties by modeling their spectra, and because they appear to be a large fraction of the overall neutron-star population. Here, we describe a series of XMM-Newton observations of the nearby INS RX J0806.4−4123, taken as part of larger program of timing studies. From these, we limit the spin-down rate to $\dot{\nu }=(-4.3\pm 2.3) \times 10^{-16}\,{\rm Hz}\,{\rm s}^{-1}$. This constrains the dipole magnetic field to be <3.7 × 10¹³ G at 2σ, significantly less than the field of ∼10¹⁴ G implied by simple models for the X-ray absorption found at 0.45 keV. We confirm that the spectrum is thermal and stable (to within a few percent), but find that the 0.45 keV absorption feature is broader and more complex than previously thought. Considering the population of INSs, we find that magnetic field decay from an initial field of ≲3 × 10¹⁴ G accounts most naturally for their timing and spectral properties, both qualitatively and in the context of the models for field decay of Pons and collaborators.

To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ∼ 0.35. We draw on multi-wavelength observations⁹that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ_1D =  303–580 km s⁻¹) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find that (1) the fraction of supergroup galaxies with SFR_IR ⩾ 3 M_☉ yr⁻¹ is 4 times higher than in the cluster (32% ±  5% versus 7% ±  2%); (2) the supergroup's infrared luminosity function confirms that it has a higher density of IR members compared to the cluster and includes bright IR sources (log(L_IR)[erg s⁻¹] >45) not found in galaxy clusters at z ≲ 0.35; and (3) there is a strong trend of decreasing 24 μm fraction with increasing galaxy density, i.e., an infrared–density relation, not observed in the cluster. These dramatic differences are surprising because the early-type fraction in the supergroup is already as high as in clusters, i.e., the timescales for morphological transformation cannot be strongly coupled to when the star formation is completely quenched. The supergroup has a significant fraction (∼17%) of luminous, low-mass (10.0 < log(M_*)[M_☉] < 10.6), SFR_IR ⩾ 3 M_☉ yr⁻¹ members that are outside the group cores (R_proj ⩾ 0.5 Mpc); once their star formation is quenched, most will evolve into faint red galaxies. Our analysis indicates that the supergroup's 24 μm population also differs from that in the field: (1) despite the supergroup having twice the fraction of E/S0s as the field, the fraction of SFR_IR ⩾ 3 M_☉ yr⁻¹ galaxies is comparable in both environments, and (2) the supergroup's IR luminosity function has a higher L*_IR than that previously measured for the field.

We estimated photospheric velocities by separately applying the Fourier Local Correlation Tracking and Differential Affine Velocity Estimator methods to 2708 co-registered pairs of SOHO/MDI magnetograms, with nominal 96 minute cadence and ∼2'' pixels, from 46 active regions (ARs) from 1996 to 1998 over the time interval τ₄₅ when each AR was within 45° of disk center. For each magnetogram pair, we computed the reprojected, average estimated radial magnetic field, $\tilde{B}_R$; and each tracking method produced an independently estimated flow field, u. We then quantitatively characterized these magnetic and flow fields by computing several extensive and intensive properties of each; extensive properties scale with AR size, while intensive properties do not depend directly on AR size. Intensive flow properties included moments of speeds, horizontal divergences, and radial curls; extensive flow properties included sums of these properties over each AR, and a crude proxy for the ideal Poynting flux, $S_R = \sum |{\bf u}| \tilde{B}_R^2$. Several quantities derived from $\tilde{B}_R$ were also computed, including: Φ, the total unsigned flux; R, a measure of the unsigned flux near strong-field polarity inversion lines; and $\sum \tilde{B}_R^2$. Next, using correlation and discriminant analysis, we investigated the associations between these properties and flares from the GOES flare catalog, when averaged over both τ₄₅ and shorter time windows of 6 and 24 hr. Our AR sample included both flaring and flare-quiet ARs; the latter did not flare above GOES C1.0 level during τ₄₅. Among magnetic properties, we found R to be most strongly associated with flare flux. Among extensive flow properties, the proxy Poynting flux, S_R, was most strongly associated with flare flux, at a level comparable to that of R. All intensive flow properties studied were more poorly associated with flare flux than these extensive properties. Past flare activity was also associated with future flare occurrence. The largest coefficients of determination from correlations with flare flux that we performed are ∼0.25, implying no single variable that we considered can explain the majority of variability in average flare flux.

We describe a three-dimensional simulation of a 1 M_☉ solar-type star approaching a 10⁶M_☉ black hole on a parabolic orbit with a pericenter distance well within the tidal radius. While falling toward the black hole, the star is not only stretched along the orbital direction but also even more severely compressed at right angles to the orbit. The overbearing degree of compression achieved shortly after pericenter leads to the production of strong shocks that largely homogenize the temperature profile of the star, resulting in surface temperatures comparable to the initial temperature of the star's core. This phenomenon, which precedes the fallback accretion phase, gives rise to a unique double-peaked X-ray signature that, if detected, may be one of the few observable diagnostics of how stars behave under the influence of strong gravitational fields. If ∼10⁶M_☉ black holes were prevalent in small or even dwarf galaxies, the nearest of such flares may be detectable by EXIST from no further away than the Virgo Cluster.

Using Chandra imaging spectroscopy and Very Large Array L-band maps, we have identified radio galaxies at P_(1.4 GHz)⩾ 3 × 10²³ W Hz⁻¹ and X-ray point sources (XPSs) at L_{(0.3–8 keV)}⩾ 10⁴² erg s⁻¹ in 11 moderate redshift (0.2 < z < 0.4) clusters of galaxies. Each cluster is uniquely chosen to have a total mass similar to predicted progenitors of the present-day Coma Cluster. Within a projected radius of 1 Mpc we detect 20 radio galaxies and 8 XPSs (three sources are detected in both X-ray and radio) confirmed to be cluster members above these limits. Of these, 75% are detected within 500 kpc (projected) of the cluster center. This result is inconsistent with a random selection from bright, red sequence ellipticals at the >99.999% level. We suggest that these active galactic nuclei (AGNs) are triggered somehow by the intracluster medium (ICM), perhaps similar to the Bondi accretion model of Allen et al. All but one of the XPSs are hosted by luminous ellipticals which otherwise show no other evidence for AGN activity. These objects are unlikely to be highly obscured AGN since there is no evidence for large amounts of X-ray or optical absorption. One XPS, in addition to possessing a pure absorption-line optical spectrum, has a large excess of light blueward of the Ca ii H&K break that could be nonthermal emission; a second XPS host galaxy probably has excess blue light. The most viable model for these sources are low-luminosity BL Lac Objects, similar to the high-energy-peaked BL Lacs (HBLs) discovered in abundance in serendipitous X-ray surveys. The expected numbers of lower luminosity FR 1 radio galaxies and HBLs in our sample converge to suggest that very deep radio and X-ray images of rich clusters will detect AGN (either X-ray or radio emitting or both) in a large fraction of bright elliptical galaxies in the inner 500 kpc. Because both the radio galaxies and the XPSs possess relativistic jets, they (and, by extension, the entire radio luminosity function) can inject heat into the ICM. Using the most recent scalings of P_jet ∝  L^0.5_r from Bîrzan et al., radio sources weaker than our luminosity limit probably contribute the majority of the heat to the ICM. Also, because these heat sources move around the cluster, AGN heating is distributed rather evenly. If a majority of ICM heating is due to large numbers of low-power radio sources, triggered into activity by the increasing ICM density as they move inward, this may be the feedback mechanism necessary to stabilize cooling in cluster cores.

The detection of polarized sources in the WMAP five-year data is a very difficult task. The maps are dominated by instrumental noise and only a handful of sources show up as clear peaks in the Q and U maps. Optimal linear filters applied at the position of known bright sources detect with a high level of significance a polarized flux P from many more sources, but estimates of P are liable to biases. Using a new technique, named the filtered fusion technique, we have detected in polarization, with a significance level greater than 99.99% in at least one WMAP channel, 22 objects, five of which, however, do not have a plausible low radio frequency counterpart and are therefore doubtful. Estimated polarized fluxes P < 400 mJy at 23 GHz were found to be severely affected by the Eddington bias. The corresponding polarized flux limit for Planck/LFI at 30 GHz, obtained via realistic simulations, is 300 mJy. We have also obtained statistical estimates of, or upper limits to the mean polarization degrees of bright WMAP sources at 23, 33, 41, and 61 GHz, finding that they are of a few percent.

In this work, we show Very Long Baseline Array data at 8 GHz (RRFID) and 15 GHz (MOJAVE) of BL Lac from 1995 to 2007 by examining the structure in the maps given by the CLEAN-point components (represented by a restoring beam of 0.1 mas). The CLEAN-point maps show a well-ordered train of individual points in the inner core jet. The result shows a narrow elongated stationary component at about 1.5 mas from the core which was interpreted as superposition of trailing components. The inner core-jet structure shows ballistic motion and a precessing ejection nozzle period of 26 years.

We present the analysis of the polycyclic aromatic hydrocarbon (PAH) spectra of a sample of 92 typical star-forming galaxies at 0.03 < z < 0.2 observed with the Spitzer intensified Reticon spectrograph (IRS). We compare the relative strengths of PAH emission features with Sloan Digital Sky Survey optical diagnostics to probe the relationship between PAH grain properties and star formation and active galactic nuclei (AGNs) activity. Short-to-long wavelength PAH ratios, and in particular the 7.7 μm-to-11.3 μm feature ratio, are strongly correlated with the star formation diagnostics D_n(4000) and Hα equivalent width, increasing with younger stellar populations. This ratio also shows a significant difference between active and non-active galaxies, with the active galaxies exhibiting weaker 7.7 μm emission. A hard radiation field as measured by $[{\rm O}\,{\scriptstyle {{\rm III}}}]/{\rm H}\beta$ and $[{\rm Ne}\,{\scriptstyle {{\rm III}}}]_{15.6 \,\mu {\rm m}}/[{\rm Ne}\,{\scriptstyle {{\rm II}}}]_{12.8 \,\mu {\rm m}}$ effects PAH ratios differently depending on whether this field results from starburst activity or an AGN. Our results are consistent with a picture in which larger PAH molecules grow more efficiently in richer media and in which smaller PAH molecules are preferentially destroyed by the AGN.

We present quasi-simultaneous, multi-frequency Very Large Array observations at 4.8, 8.4, and 22.5 GHz of a sample of 13 Wolf–Rayet (WR) stars, aimed at disentangling the nature of their radio emission and the possible detection of a non-thermal behavior in close binary systems. We detected 12 stars from our sample, for which we derived spectral information and estimated their mass-loss rates. From our data, we identified four thermal sources (WR 89, 113, 138, and 141), and three sources with a composite spectrum (similar contribution of thermal and non-thermal emission; WR 8, 98, and 156). On the other hand, from the comparison with previous observations, we confirm the non-thermal spectrum of one (WR 105), and also found evidence of a composite spectrum for WR 79a, 98a, 104, and 133. Finally, we discuss the possible scenarios to explain the nature of the emission for the observed objects.

The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single-fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.

Coronal dimmings are closely related to the footpoints of coronal mass ejections (CMEs) and, as such, offer information about CME origins and evolution. In this paper, we investigate the relationship between CME and dimming properties. In particular, we compare CME quantities for events with and without associated dimmings. We find that dimming-associated CMEs, on average, have much higher speeds than non-dimming-associated events. In fact, CMEs without an associated dimming do not appear to travel faster than 800 km s⁻¹, i.e., the fast solar wind speed. Dimming-associated events are also more likely to be associated with flares, and those flares tend to have the highest magnitudes. We propose that each of these phenomena is affected by the energy available in the source region. Highly energetic source regions produce fast CMEs that are accompanied by larger flares and visible dimmings, while less energetic source regions produce slow CMEs that are accompanied by smaller flares and may or may not have dimmings. The production of dimmings in the latter case may depend on a number of factors including initiation height of the CME, source region magnetic configuration, and observational effects. These results have important implications for understanding and predicting CME initiations.

The properties of elliptical galaxies are broadly consistent with simulated remnants of gas-rich mergers between spirals, motivating more detailed studies of the imprint of this formation mechanism on the remnant distribution function. Gas has a strong impact on the non-Gaussian shapes of the line-of-sight velocity distributions (LOSVDs) of the merger remnant, owing to the embedded disk that forms out of the gas that retains its angular momentum during the merger, and the strong central mass concentration from the gas that falls to the center. The deviations from Gaussianity are effectively parameterized by the Gauss–Hermite moments h₃ and h₄, which are related to the skewness and kurtosis of the LOSVDs. We quantify the dependence of the (h₃, h₄)–v/σ relations on the initial gas fraction f_gas of the progenitor disks in 1:1 mergers, using Gadget-2 simulations including star formation, radiative cooling, and feedback from supernovae and active galactic nuclei. For f_gas ≲ 15%, the overall correlation between h₃ and v/σ is weak, consisting of a flat negatively correlated component arising from edge-on viewing angles plus a steep positively correlated part from more face-on projections. The spread in v/σ values decreases toward high positive h₄, and there is a trend toward lower h₄ values as f_gas increases from 0% to 15%. For f_gas ≳ 20%, the (h₃, h₄)–v/σ distributions look quite different—there is a tight negative h₃–v/σ correlation, and a wide spread in v/σ values at all h₄, in much better agreement with observations. Re-mergers of the high-f_gas remnants (representing dry mergers) produce slowly rotating systems with near-Gaussian LOSVDs. We explain all of these trends in terms of the underlying orbit structure of the remnants, as molded by their dissipative formation histories.

Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous outflows of a few to 50 km s⁻¹ from active regions (ARs). These outflows are most prominent at the AR boundary and appear over monopolar magnetic areas. They are linked to strong non-thermal line broadening and are stronger in hotter EUV lines. The outflows persist for at least several days. Using Hinode EIS and X-Ray Telescope observations of AR 10942 coupled with magnetic modeling, we demonstrate that the outflows originate from specific locations of the magnetic topology where field lines display strong gradients of magnetic connectivity, namely quasi-separatrix layers (QSLs), or in the limit of infinitely thin QSLs, separatrices. We found the strongest AR outflows to be in the vicinity of QSL sections located over areas of strong magnetic field. We argue that magnetic reconnection at QSLs separating closed field lines of the AR and either large-scale externally connected or "open" field lines is a viable mechanism for driving AR outflows which are likely sources of the slow solar wind.

We provide a systematic measurement of the rest-frame UV continuum slope β over a wide range in redshift (z ∼ 2–6) and rest-frame UV luminosity (0.1 L*_{z = 3} to 2 L*_{z = 3}) to improve estimates of the star formation rate (SFR) density at high redshift. We utilize the deep optical and infrared data (Advanced Camera for Surveys/NICMOS) over the Chandra Deep Field-South and Hubble Deep Field-North Great Observatories Origins Deep Survey fields, as well as the UDF for our primary UBVi "dropout" Lyman Break Galaxy sample. We also use strong lensing clusters to identify a population of very low luminosity, high-redshift dropout galaxies. We correct the observed distributions for both selection biases and photometric scatter. We find that the UV-continuum slope of the most luminous galaxies is substantially redder at z ∼ 2–4 than it is at z ∼ 5–6 (from ∼−2.4 at z ∼ 6 to ∼−1.5 at z ∼ 2). Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z ∼ 2.5 and z ∼ 4. We do not find a large number of galaxies with β's as red as −1 in our dropout selections at z ∼ 4, and particularly at z ≳ 5, even though such sources could be readily selected from our data (and also from Balmer Break Galaxy searches at z ∼ 4). This suggests that star-forming galaxies at z ≳ 5 almost universally have very blue UV-continuum slopes, and that there are not likely to be a substantial number of dust-obscured galaxies at z ≳ 5 that are missed in "dropout" searches. Using the same relation between UV-continuum slope and dust extinction as has been found to be appropriate at both z ∼ 0 and z ∼ 2, we estimate the average dust extinction of galaxies as a function of redshift and UV luminosity in a consistent way. As expected, we find that the estimated dust extinction increases substantially with cosmic time for the most UV luminous galaxies, but remains small (≲2 times) at all times for lower luminosity galaxies. Because these same lower luminosity galaxies dominate the luminosity density in the UV continuum, the overall dust extinction correction remains modest at all redshifts and the evolution of this correction with redshift is only modest. We include the contribution from ultra-luminous IR galaxies in our SFR density estimates at z ∼ 2–6, but find that they contribute only ∼20% of the total at z ∼ 2.5 and ≲10% at z ≳ 4.

We describe an ultraviolet spectroscopic survey of interstellar high-velocity cloud (HVC) absorption in the strong λ1206.500 line of Si iii using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Because the Si iii line is 4–5 times stronger than O vi λ1031.926, it provides a sensitive probe of ionized gas down to column densities N_Si iii ≈ 5 × 10¹¹ cm⁻² at Si iii equivalent width 10 mÅ. We detect high-velocity Si iii over 91% ± 4% of the sky (53 of 58 sight lines); 59% of the HVCs show negative local standard of rest velocities. The mean HVC column density per sight line is 〈log N_Si iii〉 = 13.19 ± 0.45, while the mean for all 90 velocity components is 12.92 ± 0.46. Lower limits due to Si iii line saturation are included in this average, so the actual mean/median values are even higher. The Si iii appears to trace an extensive ionized component of Galactic halo gas at temperatures 10^4.0–4.5 K indicative of a cooling flow. Photoionization models suggest that typical Si iii absorbers with 12.5 < log N_Si iii < 13.5 have total hydrogen column densities N_H ≈ 10¹⁸–10¹⁹ cm⁻² for gas of hydrogen density n_H ≈ 0.1 cm⁻³ and 10% solar metallicity. With typical neutral fractions N_H i/N_H ≈ 0.01, these HVCs may elude even long-duration 21 cm observations at Arecibo, the EVLA, and other radio facilities. However, if Si iii is associated with higher density gas, n_H ⩾ 1 cm⁻³, the corresponding neutral hydrogen could be visible in deep observations. This reservoir of ionized gas may contain 10⁸ M_☉ and produce a mass infall rate of 1 M_☉ yr⁻¹ to the Galactic disk.

We present an improved analysis of the final data set from the QUaD experiment. Using an improved technique to remove ground contamination, we double the effective sky area and hence increase the precision of our cosmic microwave background (CMB) power spectrum measurements by ∼30% versus that previously reported. In addition, we have improved our modeling of the instrument beams and have reduced our absolute calibration uncertainty from 5% to 3.5% in temperature. The robustness of our results is confirmed through extensive jackknife tests, and by way of the agreement that we find between our two fully independent analysis pipelines. For the standard six-parameter ΛCDM model, the addition of QUaD data marginally improves the constraints on a number of cosmological parameters over those obtained from the WMAP experiment alone. The impact of QUaD data is significantly greater for a model extended to include either a running in the scalar spectral index, or a possible tensor component, or both. Adding both the QUaD data and the results from the Arcminute Cosmology Bolometer Array Receiver experiment, the uncertainty in the spectral index running is reduced by ∼25% compared to WMAP alone, while the upper limit on the tensor-to-scalar ratio is reduced from r < 0.48 to r < 0.33 (95% c.l.). This is the strongest limit on tensors to date from the CMB alone. We also use our polarization measurements to place constraints on parity-violating interactions to the surface of last scattering, constraining the energy scale of Lorentz violating interactions to <1.5 × 10⁻⁴³ GeV (68% c.l.). Finally, we place a robust upper limit on the strength of the lensing B-mode signal. Assuming a single flat band power between ℓ = 200 and ℓ = 2000, we constrain the amplitude of B-modes to be <0.57 μK² (95% c.l.).

The vigorous magnetic dynamo action achieved within the convective cores of A-type stars may be influenced by fossil magnetic fields within their radiative envelopes. We study such effects through three-dimensional simulations that model the inner 30% by radius of a 2 M_☉ A-type star, capturing the convective core and a portion of the overlying radiative envelope within our computational domain. We employ the three-dimensional anelastic spherical harmonic code to model turbulent dynamics within a deep rotating spherical shell. The interaction between a fossil field and the core dynamo is examined by introducing a large-scale magnetic field into the radiative envelope of a mature A star dynamo simulation. We find that the inclusion of a twisted toroidal fossil field can lead to a remarkable transition in the core dynamo behavior. Namely, a super-equipartition state can be realized in which the magnetic energy built by dynamo action is 10-fold greater than the kinetic energy of the convection itself. Such strong-field states may suggest that the resulting Lorentz forces should seek to quench the flows, yet we have achieved super-equipartition dynamo action that persists for multiple diffusion times. This is achieved by the relative co-alignment of the flows and magnetic fields in much of the domain, along with some lateral displacements of the fastest flows from the strongest fields. Convection in the presence of such strong magnetic fields typically manifests as 4–6 cylindrical rolls aligned with the rotation axis, each possessing central axial flows that imbue the rolls with a helical nature. The roll system also possesses core-crossing flows that couple distant regions of the core. We find that the magnetic fields exhibit a comparable global topology with broad, continuous swathes of magnetic field linking opposite sides of the convective core. We have explored several poloidal and toroidal fossil field geometries, finding that a poloidal component is essential for a transition to super-equipartition to occur.

We present the analysis of the X-ray brightness and temperature profiles for six clusters belonging to both the Cool Core (CC) and Non Cool Core (NCC) classes, in terms of the Supermodel (SM) developed by Cavaliere et al. Based on the gravitational wells set by the dark matter (DM) halos, the SM straightforwardly expresses the equilibrium of the intracluster plasma (ICP) modulated by the entropy deposited at the boundary by standing shocks from gravitational accretion, and injected at the center by outgoing blast waves from mergers or from outbursts of active galactic nuclei. The cluster set analyzed here highlights not only how simply the SM represents the main dichotomy CC versus NCC clusters in terms of a few ICP parameters governing the radial entropy run, but also how accurately it fits even complex brightness and temperature profiles. For CC clusters like A2199 and A2597, the SM with a low level of central entropy straightforwardly yields the characteristic peaked profile of the temperature marked by a decline toward the center, without requiring currently strong radiative cooling and high mass deposition rates. NCC clusters like A1656 require instead a central entropy floor of a substantial level, and some like A2256 and even more A644 feature structured temperature profiles that also call for a definite floor extension; in such conditions the SM accurately fits the observations, and suggests that in these clusters the ICP has been just remolded by a merger event, in the way of a remnant cool core. The SM also predicts that DM halos with high concentration should correlate with flatter entropy profiles and steeper brightness in the outskirts; this is indeed the case with A1689, for which from X-rays we find concentration values c ∼ 10, the hallmark of an early halo formation. Thus, we show the SM to constitute a fast tool not only to provide wide libraries of accurate fits to X-ray temperature and density profiles, but also to retrieve from the ICP archives specific information concerning the physical histories of DM and baryons in the inner and the outer cluster regions.

We have proposed that the first phase of stellar evolution in the history of the universe may be dark (matter powered) stars (DSs), luminous objects powered by dark matter (DM) heating rather than by nuclear fusion, and in this paper we examine the history of these DSs. The power source is annihilation of weakly interacting massive particles (WIMPs) which are their own antiparticles. These WIMPs are the best motivated DM candidates and may be discovered by ongoing direct or indirect detection searches (e.g., Fermi/GLAST) or at the Large Hadron Collider at CERN. A new stellar phase results, powered by DM annihilation as long as there is a DM fuel, from millions to billions of years. We build up the DSs from the time DM heating becomes the dominant power source, accreting more and more matter onto them. We have included many new effects in the current study, including a variety of particle masses and accretion rates, nuclear burning, feedback mechanisms, and possible repopulation of DM density due to capture. Remarkably, we find that in all these cases, we obtain the same result: the first stars are very large, 500–1000 times as massive as the Sun; as well as puffy (radii 1–10 AU), bright (10⁶–10⁷ L_☉), and cool (T_surf < 10, 000 K) during the accretion. These results differ markedly from the standard picture in the absence of DM heating, in which the maximum mass is about 140 M_☉ and the temperatures are much hotter (T_surf > 50,000 K). Hence DSs should be observationally distinct from standard Pop III stars. In addition, DSs avoid the (unobserved) element enrichment produced by the standard first stars. Once the DM fuel is exhausted, the DS becomes a heavy main-sequence star; these stars eventually collapse to form massive black holes that may provide seeds for the supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate-mass black holes.

Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal galaxy (dSph) found by Zucker et al. in the Sloan Digital Sky Survey (SDSS; York et al.). In this paper, we present the first spectroscopic study of individual red giant branch stars in And X, as a part of the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) Survey. Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two spectroscopic masks over the face of the galaxy and measure radial velocities for ∼100 stars with a median accuracy of σ_v ∼ 3 km s⁻¹. The velocity histogram for this field confirms three populations of stars along the sight line: foreground Milky Way dwarfs at small negative velocities, M31 halo red giants over a broad range of velocities, and a very cold velocity "spike" consisting of 22 stars belonging to And X with v_rad = −163.8 ± 1.2 km s⁻¹. By carefully considering both the random and systematic velocity errors of these stars (e.g., through duplicate star measurements), we derive an intrinsic velocity dispersion of just σ_v = 3.9 ± 1.2 km s⁻¹ for And X, which for its size, implies a minimum mass-to-light ratio of M/L_V = 37⁺²⁶₋₁₉ assuming that the mass traces the light. Based on the clean sample of member stars, we measure the median metallicity of And X to be [Fe/H] = −1.93 ± 0.11, with a slight radial metallicity gradient. The dispersion in metallicity is large, σ([Fe/H]_phot) = 0.48, possibly hinting that the galaxy retained much of its chemical enrichment products. And X has a total integrated luminosity (M_V = −8.1 ± 0.5) that straddles the classical Local Group dSphs and the new SDSS ultra-low luminosity galaxies. The galaxy is among the most metal-poor dSphs known, especially relative to those with M_V < −8, and has the second lowest intrinsic velocity dispersion of the entire sample. Our results suggest that And X is less massive by a factor of 4 when compared to Milky Way dSphs of comparable luminosity (e.g., Draco and Ursa Minor). We discuss the potential for better understanding the formation and evolution mechanisms for M31's system of dSphs through (current) kinematic and chemical abundance studies, especially in relation to the Milky Way sample.

We report combined optical and X-ray observations of nova M31N 2007-12b. Optical spectroscopy obtained 5 days after the 2007 December outburst shows evidence of very high ejection velocities (FWHM Hα ≃ 4500 km s⁻¹). In addition, Swift X-ray data show that M31N 2007-12b is associated with a Super-Soft Source (SSS) which appeared between 21 and 35 days post-outburst and turned off between then and day 169. Our analysis implies that M_WD ≳ 1.3 M_☉ in this system. The optical light curve, spectrum, and X-ray behavior are consistent with those of a recurrent nova. Hubble Space Telescope observations of the pre-outburst location of M31N 2007-12b reveal the presence of a coincident stellar source with magnitude and color very similar to the Galactic recurrent nova RS Ophiuchi at quiescence, where the red giant secondary dominates the emission. We believe that this is the first occasion on which a nova progenitor system has been identified in M31. However, the greatest similarities of outburst optical spectrum and SSS behavior are with the supposed Galactic recurrent nova V2491 Cygni. A previously implied association of M31N 2007-12b with nova M31N 1969-08a is shown to be erroneous, and this has important lessons for future searches for recurrent novae in extragalactic systems. Overall, we show that suitable complementary X-ray and optical observations can be used not only to identify recurrent nova candidates in M31, but also to determine subtypes and important physical parameters of these systems. Prospects are therefore good for extending studies of recurrent novae into the Local Group with the potential to explore in more detail such important topics as their proposed link to Type Ia Supernovae.

We analyze the M1.1 flare event peaked at 07:20:00 UT on 2004 December 1 mainly from radio and hard X-ray (HXR) observations. By eliminating the thermal component from the observed total radio emission flux, the non-thermal part of the radio and HXR burst process is investigated in a self-consistent way. The spectral index of energetic electrons deduced from the radio burst evolves as a Soft–Hard–Hard pattern and that from HXR as a Soft–Hard–Soft pattern corresponding to an initial-main-decay phase. The trap-plus-precipitation model is applied in the kinetic process of energetic electrons for this flare event. The radio fluxes at six frequencies selected from the 2.6–7.6 GHz range are fitted with a gyrosynchrotron radiation mechanism. It is found that a linearly increasing electron escape rate can best fit to the observed radio fluxes from 07:00:00 UT to 07:40:00 UT and the slope of the electron escape rate for the six selected frequencies decreases with increasing frequency. During the decay phase from 07:15:00 UT to 07:20:00 UT, the hardened spectrum of the radio burst may be due to the increasing amount of trapped electrons with higher energy by a lower escape rate. Meanwhile, the increasing amount of precipitating electrons with a lower energy band may soften the HXR spectrum. In the decay phase after 07:20:00 UT, thermal emission is the dominating component for the radio burst.

Collimated supersonic flows in laboratory experiments behave in a similar manner to astrophysical jets provided that radiation, viscosity, and thermal conductivity are unimportant in the laboratory jets and that the experimental and astrophysical jets share similar dimensionless parameters such as the Mach number and the ratio of the density between the jet and the ambient medium. When these conditions apply, laboratory jets provide a means to study their astrophysical counterparts for a variety of initial conditions, arbitrary viewing angles, and different times, attributes especially helpful for interpreting astronomical images where the viewing angle and initial conditions are fixed and the time domain is limited. Experiments are also a powerful way to test numerical fluid codes in a parameter range in which the codes must perform well. In this paper, we combine images from a series of laboratory experiments of deflected supersonic jets with numerical simulations and new spectral observations of an astrophysical example, the young stellar jet HH 110. The experiments provide key insights into how deflected jets evolve in three dimensions, particularly within working surfaces where multiple subsonic shells and filaments form, and along the interface where shocked jet material penetrates into and destroys the obstacle along its path. The experiments also underscore the importance of the viewing angle in determining what an observer will see. The simulations match the experiments so well that we can use the simulated velocity maps to compare the dynamics in the experiment with those implied by the astronomical spectra. The experiments support a model where the observed shock structures in HH 110 form as a result of a pulsed driving source rather than from weak shocks that may arise in the supersonic shear layer between the Mach disk and bow shock of the jet's working surface.

We present a new Suzaku observation of the obscured active galactic nucleus in NGC 1365, revealing an unexpected excess of X-rays above 20 keV of at least a factor ∼2 with respect to the extrapolation of the best-fitting 3–10 keV model. Additional Swift-BAT and Integral-IBIS observations show that the 20–100 keV is concentrated within ∼1.5 arcmin from the center of the galaxy, and is not significantly variable on timescales from days to years. A comparison of this component with the 3–10 keV emission, which is characterized by a rapidly variable absorption, suggests a complex structure of the circumnuclear medium, consisting of at least two distinct components with rather different physical properties, one of which covers >80% of the source with a column density N_H ∼ 3–4×10²⁴ cm⁻². An alternative explanation is the presence of a double active nucleus in the center of NGC 1365.

We present the Suzaku spectroscopic study of the Galactic middle-aged supernova remnant (SNR) IC 443. The X-ray spectrum in the 1.75–6.0 keV band is described by an optically thin thermal plasma with the electron temperature of ∼0.6 keV and several additional Lyman lines. We robustly detect, for the first time, strong radiative recombination continua (RRC) of H-like Si and S around at 2.7 and 3.5 keV. The ionization temperatures of Si and S determined from the intensity ratios of the RRC to He-like Kα lines are ∼1.0 keV and ∼1.2 keV, respectively. We thus find firm evidence for an extremely overionized (recombining) plasma. As the origin of the overionization, a thermal conduction scenario argued in previous work is not favored in our new results. We propose that the highly ionized gas was made at the initial phase of the SNR evolution in dense regions around a massive progenitor, and the low electron temperature is due to a rapid cooling by an adiabatic expansion.

Shock breakout is the brightest radiative phenomenon in a Type II supernova (SN). Although it was predicted to be bright, direct observation is difficult due to the short duration and X-ray/ultraviolet-peaked spectra. First entire observations of the shock breakouts of Type II Plateau SNe (SNe IIP) were reported in 2008 by ultraviolet and optical observations by the Galaxy Evolution Explorer satellite and supernova legacy survey (SNLS), named SNLS-04D2dc and SNLS-06D1jd. We present multicolor light curves of an SN IIP, including the shock breakout and plateau, calculated with a multigroup radiation hydrodynamical code STELLA and an evolutionary progenitor model. The synthetic multicolor light curves reproduce well the observations of SNLS-04D2dc. This is the first study to reproduce the ultraviolet light curve of the shock breakout and the optical light curve of the plateau consistently. We conclude that SNLS-04D2dc is the explosion with a canonical explosion energy 1.2 × 10⁵¹ erg and that its progenitor is a star with a zero-age main-sequence mass 20 M_☉ and a presupernova radius 800 R_☉. The model demonstrates that the peak apparent B-band magnitude of the shock breakout would be m_B ∼ 26.4 mag if an SN identical to SNLS-04D2dc occurs at a redshift z = 1, which can be reached by 8m-class telescopes. The result evidences that the shock breakout has a great potential to detect SNe IIP at z ≳ 1.

The large scatters of luminosity relations of gamma-ray bursts (GRBs) have been one of the most important reasons that prevent the extensive applications of GRBs in cosmology. In this paper, we extend the two-dimensional (2D) luminosity relations with τ_lag, V, E_peak, and τ_RT as the luminosity indicators to three dimensions (3D) using the same set of luminosity indicators to explore the possibility of decreasing the intrinsic scatters. We find that, for the 3D luminosity relations between the luminosity and an energy scale (E_peak) and a timescale (τ_lag or τ_RT), their intrinsic scatters are considerably smaller than those of corresponding 2D luminosity relations. Enlightened by the result and the definition of the luminosity (energy released in units of time), we discussed possible reasons behind this result, which may give us helpful suggestions on seeking more precise luminosity relations for GRBs in the future.

We present an analysis of the active galaxy SDSS J131642.90+175332.5, which is remarkable because all of its narrow emission lines are double-peaked, and because it additionally shows an extra broad component (FHWM ∼ 1400 km s⁻¹) in most of its forbidden lines, peaking in between the two narrow systems. The peaks of the two narrow systems are separated by 400–500 km s⁻¹ in velocity space. The spectral characteristics of double-peaked [O iii] emission have previously been interpreted as a signature of dual or binary active galactic nuclei (AGNs), among other models. In the context of the binary scenario, SDSS J131642.90+175332.5 is a particularly good candidate because not just one line but all of its emission lines are double-peaked. However, we also discuss a number of other scenarios which can potentially account for double-peaked narrow emission lines, including projection effects, a two-sided outflow, jet–cloud interactions, special narrow-line region (NLR) geometries (disks, bars, or inner spirals), and a galaxy merger with only one AGN illuminating two NLRs. We argue that the similarity of the emission-line ratios in both systems, and the presence of the very unusual broad component at intermediate velocity, makes a close pair of unrelated AGNs unlikely, and rather argues for processes in a single galaxy or merger. We describe future observations that can distinguish between these remaining possibilities.

We report optical observations of the luminous blue variable (LBV) HR Carinae which show that the star has reached a visual minimum phase in 2009. More importantly, we detected absorptions due to Si iv λλ4088–4116. To match their observed line profiles from 2009 May, a high rotational velocity of v_rot ≃ 150 ± 20 km s^-1 is needed (assuming an inclination angle of 30°), implying that HR Car rotates at ≃0.88 ± 0.2 of its critical velocity for breakup (v_crit). Our results suggest that fast rotation is typical in all strong-variable, bona fide galactic LBVs, which present S-Dor-type variability. Strong-variable LBVs are located in a well-defined region of the HR diagram during visual minimum (the "LBV minimum instability strip"). We suggest this region corresponds to where v_crit is reached. To the left of this strip, a forbidden zone with v_rot/v_crit>1 is present, explaining why no LBVs are detected in this zone. Since dormant/ex LBVs like P Cygni and HD 168625 have low v_rot, we propose that LBVs can be separated into two groups: fast-rotating, strong-variable stars showing S-Dor cycles (such as AG Car and HR Car) and slow-rotating stars with much less variability (such as P Cygni and HD 168625). We speculate that supernova (SN) progenitors which had S-Dor cycles before exploding (such as in SN 2001ig, SN 2003bg, and SN 2005gj) could have been fast rotators. We suggest that the potential difficulty of fast-rotating Galactic LBVs to lose angular momentum is additional evidence that such stars could explode during the LBV phase.

We present high-resolution (R ∼ 60,000) optical spectra of a carefully selected sample of heavily obscured and presumably massive O-rich asymptotic giant branch (AGB) stars in the Magellanic Clouds. We report the discovery of strong Rb i lines at 7800 Å in four Rb-rich LMC stars at luminosities equal to or greater than the standard adopted luminosity limit for AGB stars (M_bol ∼ −7.1), confirming that "hot bottom burning" may produce a flux excess in the more massive AGB stars. In the SMC sample, just one of the five stars with M_bol < −7.1 was detected in Rb; the other stars may be massive red supergiants. The Rb-rich LMC AGB stars might have stellar masses of at least ∼6–7 M_☉. Our abundance analyses show that these Rb-rich stars are extremely enriched in Rb by up to 10³–10⁵ times solar but seem to have only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a severe problem for the s-process, even if the ²²Ne source is operational as expected for massive AGB stars; it is not possible to synthesize copious amounts of Rb without also overproducing Zr. The solution to the problem may lie with an incomplete present understanding of the atmospheres of luminous AGB stars.

We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this "nearly aligned moving spot model" may also explain the intermittent accretion-powered pulsations that have been detected in three weakly magnetic accreting neutron stars. We show that movement of the emitting area from very close to the spin axis to ∼10° away can increase the fractional rms amplitude from ≲0.5%, which is usually undetectable with current instruments, to a few percent, which is easily detectable. The second harmonic of the spin frequency usually would not be detected, in agreement with observations. The model produces intermittently detectable oscillations for a range of emitting area sizes and beaming patterns, stellar masses and radii, and viewing directions. Intermittent oscillations are more likely in stars that are more compact. In addition to explaining the sudden appearance of accretion-powered millisecond oscillations in some neutron stars with millisecond spin periods, the model explains why accretion-powered millisecond oscillations are relatively rare and predicts that the persistent accretion-powered millisecond oscillations of other stars may become undetectable for brief intervals. It suggests why millisecond oscillations are frequently detected during the X-ray bursts of some neutron stars but not others and suggests mechanisms that could explain the occasional temporal association of intermittent accretion-powered oscillations with thermonuclear X-ray bursts.

We report evidence for an anti-correlation between spin temperature T_s and metallicity [Z/H], detected at 3.6σ significance in a sample of 26 damped Lyα absorbers (DLAs) at redshifts 0.09 < z < 3.45. The anti-correlation is detected at 3σ significance in a sub-sample of 20 DLAs with measured covering factors, implying that it does not stem from low covering factors. We obtain T_s = (−0.68 ± 0.17) × [Z/H] + (2.13 ± 0.21) from a linear regression analysis. Our results indicate that the high T_s values found in DLAs do not arise from differences between the optical and radio sightlines, but are likely to reflect the underlying gas temperature distribution. The trend between T_s and [Z/H] can be explained by the larger number of radiation pathways for gas cooling in galaxies with high metal abundances, resulting in a high cold gas fraction, and hence, a low spin temperature. Conversely, low-metallicity galaxies have fewer cooling routes, yielding a larger warm gas fraction and a high T_s. Most DLAs at z > 1.7 have low metallicities, [Z/H] <−1, implying that the H i in high-z DLAs is predominantly warm. The anti-correlation between T_s and [Z/H] is consistent with the presence of a mass–metallicity relation in DLAs, suggested by the tight correlation between DLA metallicity and the kinematic widths of metal lines. Most high-z DLAs are likely to arise in galaxies with low masses (M_vir < 10^10.5M_☉), low metallicities ([Z/H] <−1), and low cold gas fractions.

We report the redshift of a distant, highly obscured submillimeter galaxy (SMG), based entirely on the detection of its CO line emission. We have used the newly commissioned Eight MIxer Receiver at the IRAM 30 m telescope, with its 8 GHz of instantaneous dual-polarization bandwidth, to search the 3 mm atmospheric window for CO emission from SMM J14009+0252, a bright SMG detected in SCUBA Lens Survey. A detection of the CO(3–2) line in the 3 mm window was confirmed via observations of CO(5–4) in the 2 mm window. Both lines constrain the redshift of SMM J14009+0252 to z = 2.9344, with high precision (δz = 2 × 10⁻⁴). Such observations will become routine in determining redshifts in the era of ALMA.

Relying purely on solar photospheric magnetic field measurements that cover most of solar cycle 23 (1996–2005), we calculate the total relative magnetic helicity injected into the solar atmosphere, and eventually shed into the heliosphere, over the latest cycle. Large active regions dominate the helicity injection process with ∼5.7 × 10⁴⁵ Mx² of total injected helicity. The net helicity injected is ≲1% of the above output. Peculiar active-region plasma flows account for ∼80% of this helicity; the remaining ∼20% is due to solar differential rotation. The typical helicity per active-region CME ranges between (1.8–7) × 10⁴² Mx² depending on the CME velocity. Accounting for various minor underestimation factors, we estimate a maximum helicity injection of ∼6.6 × 10⁴⁵ Mx² for solar cycle 23. Although no significant net helicity exists over both solar hemispheres, we recover the well-known hemispheric helicity preference, which is significantly enhanced by the solar differential rotation. We also find that helicity injection in the solar atmosphere is an inherently disorganized, impulsive, and aperiodic process.

We report mid-infrared interferometric measurements (based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, programme number 081.B-0092(A)) with ∼10 mas resolution, which resolve the warm (T = 285⁺²⁵₋₅₀ K) thermal emission at the center of NGC 4151. Using pairs of Very Large Telescope 8.2 m telescopes with the Mid-infrared interferometric instrument and by comparing the data to a Gaussian model, we determined the diameter of the dust emission region, albeit only along one position angle, to be (2.0 ± 0.4) pc (FWHM). This is the first size and temperature estimate for the nuclear warm dust distribution in a Seyfert 1 galaxy. The parameters found are comparable to those in Seyfert 2 galaxies, thus providing direct support for the unified model. Using simple analytic temperature distributions, we find that the mid-infrared emission is probably not the smooth continuation of the hot nuclear source that is marginally resolved with K-band interferometry. We also detected weak excess emission around 10.5 μm in our shorter baseline observation, possibly indicating that silicate emission is extended to the parsec scale.

Recent observations with the Galaxy Evolution Explorer (GALEX) show strong unexpected ultraviolet (UV) excess in the spectrum of brightest cluster galaxies (BCGs). It is believed that the excess UV signal is produced by old and evolved core-He burning stars, and the UV flux strength could be greatly enhanced if the progenitor stars have a high value of He abundance. In this work, we propose that the sedimentation process can greatly enhance the He abundance in BCGs. Our model predicts that the UV flux strength is stronger in more massive, low-redshift, and dynamically relaxed BCGs. These predictions are testable with the current generation of GALEX+SDSS observations.

The results from Suzaku observations of the central region of the Perseus cluster are presented. Deep exposures with the X-ray Imaging Spectrometer provide high-quality X-ray spectra from the intracluster medium. X-ray lines from helium-like Cr and Mn have been detected significantly for the first time in clusters. In addition, elemental abundances of Ne, Mg, Si, S, Ar, Ca, Fe, and Ni are accurately measured within 10' (or 220 kpc) from the cluster center. The relative abundance ratios are found to be within a range of 0.8–1.5 times the solar value. These abundance ratios are compared with previous measurements, those in extremely metal-poor stars in the Galaxy, and theoretical models.

We examine the star formation rates (SFRs) of galaxies in a redshift slice encompassing the z = 0.834 cluster RX J0152.7 − 1357. We used a low-dispersion prism in the Inamori Magellan Areal Camera and Spectrograph to identify galaxies with z_AB < 23.3 mag in diverse environments around the cluster out to projected distances of ∼8 Mpc from the cluster center. We utilize a mass-limited sample (M > 2 × 10¹⁰M_☉) of 330 galaxies that were imaged by Spitzer MIPS at 24 μm to derive SFRs and study the dependence of specific SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show a strong decrease with increasing local density, similar to the relation at z ∼ 0. Our result contrasts with other work at z ∼ 1 that finds the SFR–density trend to reverse for luminosity-limited samples. These other results appear to be driven by star formation (SF) in lower mass systems (M ∼ 10¹⁰M_☉). Our results imply that the processes that shut down SF are present in groups and other dense regions in the field. Our data also suggest that the lower SFRs of galaxies in higher density environments may reflect a change in the ratio of star-forming to non-star-forming galaxies, rather than a change in SFRs. As a consequence, the SFRs of star-forming galaxies, in environments ranging from small groups to clusters, appear to be similar and largely unaffected by the local processes that truncate SF at z ∼ 0.8.

We present Hubble Space Telescope NIC2 morphologies of a spectroscopic sample of massive galaxies at z ∼ 2.3 by extending our sample of 9 compact quiescent galaxies (r_e ∼ 0.9 kpc) with 10 massive emission-line galaxies. The emission-line galaxies are classified by the nature of their ionized emission; there are six star-forming galaxies and four galaxies hosting an active galactic nucleus (AGN). The star-forming galaxies are the largest among the emission-line galaxies, with a median size of r_e = 2.8 kpc. The three galaxies with the highest star formation rates (≳100 M_☉ yr⁻¹) have irregular and clumpy morphologies. The AGN host galaxies are more similar to the compact quiescent galaxies in terms of their structures (r_e ∼ 1.1 kpc) and spectral energy distributions. The total sample clearly separates into two classes in a color–mass diagram: the large star-forming galaxies that form the blue cloud, and the compact quiescent galaxies on the red sequence. However, it is unclear how or even if the two classes are evolutionary related. Three out of six massive star-forming galaxies have dense cores and thus may passively evolve into compact galaxies due to fading of outer star-forming regions. For these galaxies, a reverse scenario in which compact galaxies grow inside-out by star formation is also plausible. We do caution though that the sample is small. Nonetheless, it is evident that a Hubble sequence of massive galaxies with strongly correlated galaxy properties is already in place at z > 2.

Double-peaked [O iii] profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from ∼7000 active galaxies in Sloan Digital Sky Survey DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O iii] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O iii] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at ∼1 kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about ∼10⁻², impacting on the current observational deficit of binary supermassive black holes with a probability of ∼10⁻⁴ (Boroson & Lauer).

Recent surveys have revealed a lack of close-in planets around evolved stars more massive than 1.2 M_☉. Such planets are common around solar-mass stars. We have calculated the orbital evolution of planets around stars with a range of initial masses, and have shown how planetary orbits are affected by the evolution of the stars all the way to the tip of the red giant branch. We find that tidal interaction can lead to the engulfment of close-in planets by evolved stars. The engulfment is more efficient for more-massive planets and less-massive stars. These results may explain the observed semimajor axis distribution of planets around evolved stars with masses larger than 1.5 M_☉. Our results also suggest that massive planets may form more efficiently around intermediate-mass stars.

We studied Faraday rotation measure (RM) in turbulent media with the rms Mach number of unity, using isothermal, magnetohydrodynamic turbulence simulations. Four cases with different values of initial plasma beta were considered. Our main findings are as follows. (1) There is no strong correlation between the fluctuations of magnetic field strength and gas density. So the magnetic field strength estimated with RM/DM (DM is the dispersion measure) correctly represents the true mean strength of the magnetic field along the line of sight. (2) The frequency distribution of RMs is well fitted to the Gaussian. In addition, there is a good relation between the width of the distribution of RM/$\overline{\rm RM}$ ($\overline{\rm RM}$ is the average value of RMs) and the strength of the regular field along the line of sight; the width is narrower, if the field strength is stronger. We discussed the implications of our findings in the warm ionized medium where the Mach number of turbulent motions is around unity.

In the framework of turbulence dynamo, flow motions amplify a weak seed magnetic field through the stretching of field lines. Although the amplification process has been a topic of active research, less attention has been paid to the length scales of magnetic field. In this Letter, we describe a numerical study on characteristic lengths of magnetic field in magnetohydrodynamic turbulence. We considered the case of very weak or zero mean magnetic field, which is applicable to the turbulence in the intergalactic space. Our findings are as follows. (1) At saturation, the peak of magnetic field spectrum occurs at ∼L₀/2, where L₀ is the energy injection scale, while the most energy containing scale is ∼L₀/5. The peak scale of spectrum of projected, two-dimensional field is ∼L₀. (2) During the stage of magnetic field amplification, the energy equipartition scale shows a power law increase of ∼t^1.5, while the integral and curvature scales show a linear increase. The equipartition, integral, and curvature scales saturate at ∼L₀, ∼0.3L₀, and ∼0.15L₀, respectively. (3) The coherence length of magnetic field defined in the Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) is related to the integral scale. We present a formula that expresses the standard deviation of RM, σ_RM, in terms of the integral scale and rms strength of the IGMF, and estimate that σ_RM would be ∼100 and ∼ a few rad m⁻² for clusters and filaments, respectively.

We have performed C¹⁸O (J = 1–0) mapping observations of a 20' × 20' area of the OMC-1 region in the Orion A cloud. We identified 65 C¹⁸O cores, which have a mean radius, a velocity width in FWHM, and an LTE mass of 0.18 ± 0.03 pc, 0.40 ± 0.15 km s⁻¹, and 7.2 ± 4.5 M_☉, respectively. All the cores are most likely to be gravitationally bound by considering the uncertainty in the C¹⁸O abundance. We derived a C¹⁸O core mass function, which shows a power-law-like behavior above 5 M_☉. The best-fit power-law index of −2.3 ± 0.3 is consistent with those of the dense core mass functions and the stellar initial mass function (IMF) previously derived in the OMC-1 region. This agreement strongly suggests that the power-law form of the IMF has been already determined at the density of ∼10³ cm⁻³, traced by the C¹⁸O (J = 1–0) line. Consequently, we propose that the origin of the IMF should be searched in tenuous cloud structures with densities of less than 10³ cm⁻³.