Table of contents

We present the results of modeling dust spectral energy distributions (SEDs) across the Small Magellanic Cloud (SMC) with the aim of mapping the distribution of polycyclic aromatic hydrocarbons (PAHs) in a low-metallicity environment. Using Spitzer Survey of the SMC photometry from 3.6 to 160 μm over the main star-forming regions of the Wing and Bar of the SMC along with spectral mapping observations from 5 to 38 μm from the Spitzer Spectroscopic Survey of the SMC in selected regions, we model the dust SED and emission spectrum to determine the fraction of dust in PAHs across the SMC. We use the regions of overlapping photometry and spectroscopy to test the reliability of the PAH fraction as determined from SED fits alone. The PAH fraction in the SMC is low compared to the Milky Way and variable—with relatively high fractions (q_PAH ∼1%–2%) in molecular clouds and low fractions in the diffuse interstellar medium (ISM; average 〈q_PAH〉 = 0.6%). We use the map of PAH fraction across the SMC to test a number of ideas regarding the production, destruction, and processing of PAHs in the ISM. We find weak or no correlation between the PAH fraction and the distribution of carbon asymptotic giant branch stars, the location of supergiant H i shells and young supernova remnants, and the turbulent Mach number. We find that the PAH fraction is correlated with CO intensity, peaks in the dust surface density and the molecular gas surface density as determined from 160 μm emission. The PAH fraction is high in regions of active star formation, as predicted by its correlation with molecular gas, but is suppressed in H ii regions. Because the PAH fraction in the diffuse ISM is generally very low—in accordance with previous work on modeling the integrated SED of the SMC—and the PAH fraction is relatively high in molecular regions, we suggest that PAHs are destroyed in the diffuse ISM of the SMC and/or PAHs are forming in molecular clouds. We discuss the implications of these observations for our understanding of the PAH life cycle, particularly in low-metallicity and/or primordial galaxies.

We present a close companion search around 16 known early L dwarfs using aperture masking interferometry with Palomar laser guide star adaptive optics (LGS AO). The use of aperture masking allows the detection of close binaries, corresponding to projected physical separations of 0.6–10.0 AU for the targets of our survey. This survey achieved median contrast limits of ΔK ∼ 2.3 for separations between 1.2λ/D–4λ/D and ΔK ∼ 1.4 at ⅔λ/D. We present four candidate binaries detected with moderate-to-high confidence (90%–98%). Two have projected physical separations less than 1.5 AU. This may indicate that tight-separation binaries contribute more significantly to the binary fraction than currently assumed, consistent with spectroscopic and photometric overluminosity studies. Ten targets of this survey have previously been observed with the Hubble Space Telescope as part of companion searches. We use the increased resolution of aperture masking to search for close or dim companions that would be obscured by full aperture imaging, finding two candidate binaries. This survey is the first application of aperture masking with LGS AO at Palomar. Several new techniques for the analysis of aperture masking data in the low signal-to-noise regime are explored.

After recent sensitivity upgrades at the Keck Interferometer (KI), systematic interferometric 2 μm studies of the innermost dust in nearby Seyfert nuclei are within observational reach. Here, we present the analysis of new interferometric data of NGC 4151, discussed in context of the results from recent dust reverberation, spectro-photometric, and interferometric campaigns. The complete data set gives a complex picture, in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity. KI data alone indicate two scenarios: the K-band emission is either dominated to ∼90% by size scales smaller than 30 mpc, which falls short of any dust reverberation measurement in NGC 4151 and of theoretical models of circum-nuclear dust distributions. Or contrary, and more likely, the K-band continuum emission is dominated by hot dust (≳1300 K) at linear scales of about 50 mpc. The linear size estimate varies by a few tens of percent depending on the exact morphology observed. Our interferometric, deprojected centro-nuclear dust radius estimate of 55 ±  5 mpc is roughly consistent with the earlier published expectations from circum-nuclear, dusty radiative transfer models, and spectro-photometric modeling. However, our data do not support the notion that the dust emission size scale follows the nuclear variability of NGC 4151 as an R_dust ∝  L^0.5_nuc scaling relation. Instead variable nuclear activity, lagging, and variable dust response to illumination changes need to be combined to explain the observations.

From Sloan Digital Sky Survey u'g'r'i'z' imaging, we estimate the stellar masses of the host galaxies of 70 low-redshift Type Ia supernovae (SNe Ia, 0.015 <z< 0.08) from the hosts' absolute luminosities and mass-to-light ratios. These nearby SNe were discovered largely by searches targeting luminous galaxies, and we find that their host galaxies are substantially more massive than the hosts of SNe discovered by the flux-limited Supernova Legacy Survey (SNLS). Testing four separate light curve fitters, we detect ∼2.5σ correlations of Hubble residuals with both host galaxy size and stellar mass, such that SNe Ia occurring in physically larger, more massive hosts are ∼10% brighter after light curve correction. The Hubble residual is the deviation of the inferred distance modulus to the SN, calculated from its apparent luminosity and light curve properties, away from the expected value at the SN redshift. Marginalizing over linear trends in Hubble residuals with light curve parameters shows that the correlations cannot be attributed to a light-curve-dependent calibration error. Combining 180 higher-redshift ESSENCE, SNLS, and HigherZ SNe with 30 nearby SNe whose host masses are less than 10^10.8M_☉ in a cosmology fit yields 1 + w = 0.22^+0.152_−0.108, while a combination where the 30 nearby SNe instead have host masses greater than 10^10.8 M_☉ yields 1 + w = −0.03^+0.217_−0.143. Progenitor metallicity, stellar population age, and dust extinction correlate with galaxy mass and may be responsible for these systematic effects. Host galaxy measurements will yield improved distances to SNe Ia.

We present high-resolution, near-infrared NIRSPEC observations of the fundamental rovibrational CO and H⁺₃ R(1,0), R(1,1)^u, and Q(1,0) transitions toward three early-type young stars: MWC 1080, MWC 349, and LkHα 101. These observations were performed for the purpose of constraining the physical characteristics of the interstellar material along each line of sight. Toward MWC 1080, we detected strong CO absorption and determined a column density upper limit of 1.4 × 10¹⁴ cm⁻² for H⁺₃. We infer that there is very little diffuse material along the line of sight toward MWC 1080 and that the CO absorption is consistent with an origin in the dispersing natal cloud. We detected both cold CO and H⁺₃ toward MWC 349, consistent with a diffuse cloud origin. Similarly, both CO and H⁺₃ were detected toward LkHα 101. Using a recently revised value for the cosmic ray ionization rate, we conclude that the CO absorption is consistent with a dense cloud origin while the H⁺₃ could originate in either the dense or diffuse interstellar medium. We also find no evidence for CO fractionation toward LkHα 101 as reported by Goto et al.

During the early evolution of an AM Canum Venaticorum system, helium is accreted onto the surface of a white dwarf under conditions suitable for unstable thermonuclear ignition. The turbulent motions induced by the convective burning phase in the He envelope become strong enough to influence the propagation of burning fronts and may result in the onset of a detonation. Such an outcome would yield radioactive isotopes and a faint rapidly rising thermonuclear ".Ia" supernova. In this paper, we present hydrodynamic explosion models and observable outcomes of these He shell detonations for a range of initial core and envelope masses. The peak UVOIR bolometric luminosities range by a factor of 10 (from 5 × 10⁴¹ to 5 × 10⁴² erg s⁻¹), and the R-band peak varies from M_R,peak = −15 to −18. The rise times in all bands are very rapid (<10 days), but the decline rate is slower in the red than in the blue due to a secondary near-IR brightening. The nucleosynthesis primarily yields heavy α-chain elements (⁴⁰Ca through ⁵⁶Ni) and unburnt He. Thus, the spectra around peak light lack signs of intermediate-mass elements and are dominated by Ca ii and Ti ii features, with the caveat that our radiative transfer code does not include the nonthermal effects necessary to produce He features.

We report on new sensitive CO J = 6–5 line observations of several luminous infrared galaxies (LIRGs; L_IR(8–1000 μm) ≳ 10¹¹ L_☉), 36% (8/22) of them ultraluminous infrared galaxies (ULIRGs) (L_IR>10¹² L_☉), and two powerful local active galactic nuclei (AGNs)—the optically luminous QSO PG 1119+120 and the powerful radio galaxy 3C 293—using the James Clerk Maxwell Telescope on Mauna Kea in Hawaii. We combine these observations with existing low-J CO data and dust emission spectral energy distributions in the far-infrared–submillimeter from the literature to constrain the properties of the star-forming interstellar medium (ISM) in these systems. We then build the first local CO spectral line energy distributions (SLEDs) for the global molecular gas reservoirs that reach up to high J-levels. These CO SLEDs are neither biased by strong lensing (which affects many of those constructed for high-redshift galaxies), nor suffer from undersampling of CO-bright regions (as most current high-J CO observations of nearby extended systems do). We find: (1) a significant influence of dust optical depths on the high-J CO lines, suppressing the J = 6–5 line emission in some of the most IR-luminous LIRGs, (2) low global CO line excitation possible even in vigorously star-forming systems, (3) the first case of a shock-powered high-excitation CO SLED in the radio galaxy 3C 293 where a powerful jet–ISM interaction occurs, and (4) unusually highly excitated gas in the optically powerful QSO PG 1119+120. In Arp 220 and possibly other (U)LIRGs very faint CO J = 6–5 lines can be attributed to significant dust optical depths at short submillimeter wavelengths immersing those lines in a strong dust continuum, and also causing the C⁺ line luminosity deficit often observed in such extreme starbursts. Re-analysis of the CO line ratios available for submillimeter galaxies suggests that similar dust opacities also may be present in these high-redshift starbursts, with genuinely low excitation of large amounts of SF-quiescent gas being the only other possibility for their often low CO (high-J)/(low-J) line ratios. We then present a statistical method of separating these two almost degenerate possibilities, and show that high dust optical depths at submillimeter wavelengths can impede the diagnostic potential of submillimeter/IR lines (e.g., starbursts versus AGNs as gas excitation agents), which is of particular importance for the upcoming observations of the Herschel Space Observatory and the era of ALMA.

We develop a new approach for studying flux anomalies in quadruply imaged fold lens systems. We show that in the absence of substructure, microlensing, or differential absorption, the expected flux ratios of a fold pair can be tightly constrained using only geometric arguments. We apply this technique to 11 known quadruple lens systems in the radio and infrared and compare our estimates to the Monte Carlo based results of Keeton et al. We show that a robust estimate for a flux ratio from a smoothly varying potential can be found, and at long wavelengths those lenses deviating from this ratio almost certainly contain significant substructure.

The discovery of multi-planet extrasolar systems has kindled interest in using their orbital evolution as a probe of planet formation. Accurate descriptions of planetary orbits identify systems that could hide additional planets or be in a special dynamical state, and inform targeted follow-up observations. We combine published radial velocity data with Markov Chain Monte Carlo analyses in order to obtain an ensemble of masses, semimajor axes, eccentricities, and orbital angles for each of the five dynamically active multi-planet systems: HD 11964, HD 38529, HD 108874, HD 168443, and HD 190360. We dynamically evolve these systems using 52,000 long-term N-body integrations that sample the full range of possible line-of-sight and relative inclinations, and we report on the system stability, secular evolution, and the extent of the resonant interactions. We find that planetary orbits in hierarchical systems exhibit complex dynamics and can become highly eccentric and maybe significantly inclined. Additionally, we incorporate the effects of general relativity in the long-term simulations and demonstrate that it can qualitatively affect the dynamics of some systems with high relative inclinations. The simulations quantify the likelihood of different dynamical regimes for each system and highlight the dangers of restricting simulation phase space to a single set of initial conditions or coplanar orbits.

Precision photometric redshifts will be essential for extracting cosmological parameters from the next generation of wide-area imaging surveys. In this paper, we introduce a photometric redshift algorithm, ArborZ, based on the machine-learning technique of boosted decision trees. We study the algorithm using galaxies from the Sloan Digital Sky Survey (SDSS) and from mock catalogs intended to simulate both the SDSS and the upcoming Dark Energy Survey. We show that it improves upon the performance of existing algorithms. Moreover, the method naturally leads to the reconstruction of a full probability density function (PDF) for the photometric redshift of each galaxy, not merely a single "best estimate" and error, and also provides a photo-z quality figure of merit for each galaxy that can be used to reject outliers. We show that the stacked PDFs yield a more accurate reconstruction of the redshift distribution N(z). We discuss limitations of the current algorithm and ideas for future work.

In this paper, we study the "standardized candle method" using a sample of 37 nearby (redshift z < 0.06) Type II plateau supernovae having BVRI photometry and optical spectroscopy. An analytic procedure is implemented to fit light curves, color curves, and velocity curves. We find that the V−I color toward the end of the plateau can be used to estimate the host-galaxy reddening with a precision of σ(A_V) = 0.2 mag. The correlation between plateau luminosity and expansion velocity previously reported in the literature is recovered. Using this relation and assuming a standard reddening law (R_V = 3.1), we obtain Hubble diagrams (HDs) in the BVI bands with dispersions of ∼0.4 mag. Allowing R_V to vary and minimizing the spread in the HDs, we obtain a dispersion range of 0.25–0.30 mag, which implies that these objects can deliver relative distances with precisions of 12%–14%. The resulting best-fit value of R_V is 1.4 ± 0.1.

We present a possible O viii X-ray absorption line at z = 0.117 ± 0.001 which, if confirmed, will be the first one associated with a broad H i Lyβ (BLB: FWHM = 160⁺⁵⁰₋₃₀ km s⁻¹) absorber. The absorber lies along the line of sight to the nearby (z = 0.1372) Seyfert 1 galaxy PKS 0558-504, consistent with being a WHIM filament. The X-ray absorber is marginally detected in two independent XMM-Newton spectra of PKS 0558-504, a long ∼600 ks guest-observer observation and a shorter, ∼300 ks total, calibration observation, with a combined single line statistical significance of 2.8σ (2.7σ and 1.2σ in the two spectra, respectively). When fitted with our self-consistent hybrid-photoionization WHIM models, the combined XMM-Newton spectrum is consistent with the presence of O viii Kα at z = (0.117 ± 0.001). This model gives best-fitting temperature and equivalent H column density of the absorber of log T = 6.56^+0.19_−0.17 K, and log N_H = (21.5 ± 0.3)(Z/Z_0.01☉)⁻¹ cm⁻², and predicts the marginal contribution of only two more lines within the XMM-Newton Reflection Grating Spectrometer band pass, Ne ix Kα (λ = 13.45 Å) and Fe xvii L (λ = 15.02 Å), both with equivalent widths well within the 1σ sensitivity of the combined XMM-Newton spectrum of PKS 0558-504 (EW^1σ < 3 mÅ). The lack of detection of associated O vi in the archival FUSE spectrum of PKS 0558-504 allows us to infer a tighter lower limit on the temperature, of log T>6.52 K (at 1σ). The statistical significance of this single X-ray detection is increased by the detection of BLB and complex H i Lyβ absorption in archival FUSE spectra of PKS 0558-504, at redshifts z = 0.1183 ± 0.0001 consistent with the best-fitting redshift of the X-ray absorber. The FUSE spectrum shows a broad (FWHM = 160⁺⁵⁰₋₃₀ km s⁻¹) absorption complex, which we identify as H i Lyβ z_BLB = (0.1183 ± 0.0001). The single line statistical significance of this line is 4.1σ (3.7σ if systematics are considered). A possible H i Lyα is marginally hinted in an archival low-resolution (Δλ ∼ 6 Å) International Ultraviolet Explorer (IUE) spectrum of PKS 0558-504, at a redshift of z = (0.119 ± 0.001) and with single line significance of 1.7σ. Thus, the combined significance of the three (XMM-Newton, FUSE, and IUE) independent tentative detections, is 5.2σ (5.0σ if the H i Lyα is not considered, and 4.6σ if the systematics in FUSE are considered). The detection of both metal and H lines at a consistent redshift, in this hot absorbing system, allows us to speculate on its metallicity. By associating the bulk of the X-ray absorber with the BLB line detected in the FUSE spectrum at z_BLB = 0.1183 ± 0.0001, we obtain a metallicity of 1%–4% Solar. Although the absorber is only blueshifted by ∼−6000 km s⁻¹ from the systemic redshift of PKS 0558-504, the identification of the absorbing gas with a high velocity nuclear ionized outflow, is unlikely. The physical, chemical, and dynamical properties of the detected absorber are all quite different from those typically found in the warm absorber (WA) outflows, commonly detected in Seyferts and higher luminosity quasars. WA outflow velocities typically span a range of few hundreds to ∼1–2 thousands km s⁻¹; WA metallicities, when measured, are typically found to be at least Solar; high-ionization WAs are virtually always found to coexist with lower-ionization X-ray and UV phases. All this strongly suggests that the absorber, if confirmed, is an intervening WHIM system.

Characterizing the surfaces of rocky exoplanets via their scattered light will be an essential challenge in investigating their habitability and the possible existence of life on their surfaces. We present a reconstruction method for fractional areas of different surface types from the colors of an Earth-like exoplanet. We create mock light curves for Earth without clouds using empirical data. These light curves are fitted to an isotropic scattering model consisting of four surface types: ocean, soil, snow, and vegetation. In an idealized situation where the photometric errors are only photon shot noise, we are able to reproduce the fractional areas of those components fairly well. The results offer some hope for detection of vegetation via the distinct spectral feature of photosynthesis on Earth, known as the red edge. In our reconstruction method, Rayleigh scattering due to the atmosphere plays an important role, and for terrestrial exoplanets with an atmosphere similar to our Earth, it is possible to estimate the presence of oceans and an atmosphere simultaneously.

We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06–0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected Hα and forbidden line emission in seven (22%) of these BCGs, in optical spectra obtained using the Southern Astrophysical Research Goodman spectrograph. All of these emission-line BCGs occupy clusters classified as cool cores (CCs) based on the central cooling time in the cluster core, for an emission-line incidence rate of 70% for BCGs in REXCESS CC clusters. Significant correlations between the Hα equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the Hα emitters inhabit systems with short central cooling times and high central intracluster medium densities. Estimates of the star formation rates based on Hα and UV excesses are consistent with each other in these seven systems, ranging from 0.1to8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray-selected samples (∼35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples (∼10%–15%). The UV–optical colors (UVW1 − R ∼4.7 ± 0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV–optical colors with optical luminosity, R–K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak (〈w〉). The lack of such trends in these massive galaxies, particularly the ones lacking emission lines, suggests that the proportion of UV-emitting (200–300 nm) stars is insensitive to galaxy mass, cluster mass, cluster relaxation, and recent evolution, over the range of this sample.

Observations of Hercules X-1 by the Extreme Ultraviolet Explorer covering most of the 35 day cycle are reported here. This is the only long extreme ultraviolet (EUV) observation of Her X-1. Simultaneous X-ray observations with the Rossi X-ray Timing Explorer All-Sky Monitor (RXTE/ASM) X-ray show that Her X-1 is in an X-ray anomalous low state. The first 4 days are also observed with the RXTE proportional counter array (PCA), which shows that the X-ray properties are nearly the same as for normal low states in Her X-1 with flux reduced by a factor of 2. In contrast, the EUV emission from Her X-1 is reduced by a factor of ∼4 compared to normal low states. The twisted-tilted accretion disk responsible for the normal 35 day X-ray cycle can be modified to explain this behavior. An increased disk twist reduces the X-ray illumination of HZ Her by a factor of ∼2 and of the disk surface by a somewhat larger factor, leading to a larger reduction in EUV flux compared to X-ray flux.

We study the kinematics of GALEX-selected Hα knots in the outer disk (beyond R₂₅) of NGC 628 (M74), a galaxy representative of large, undisturbed, extended UV (type 1 XUV) disks. Our spectroscopic target sample of 235 of the bluest UV knots surrounding NGC 628 yielded 15 Hα detections (6%), roughly the number expected given the different mean ages of the two populations. The measured vertical velocity dispersion of the Hα knots between 1and1.8 R₂₅ (13.5–23.2 kpc) is <11 km s⁻¹. We assume that the Hα knots trace an "intermediate" vertical mass density distribution (between the isothermal sech²(z) and exponential distributions) with a constant scale height across the outer disk (h_z = 700 pc) and estimate a total surface mass density of 7.5 M_☉ pc⁻². This surface mass density can be accounted for by the observed gas and stars in the outer disk (little or no dark matter in the disk is required). The vertical velocity dispersion of the outer disk Hα knots nearly matches that measured from older planetary nebulae near the outskirts of the optical disk by Herrmann et al., suggesting a low level of scattering in the outer disk. A dynamically cold stellar component extending nearly twice as far as the traditional optical disk poses interesting constraints on the accretion history of the galaxy.

We present Chandra X-ray Observatory archival observations of the supernova remnant 1E0102.2−7219, a young oxygen-rich remnant in the Small Magellanic Cloud. Combining 28 ObsIDs for 324 ks of total exposure time, we present an Advanced CCD Imaging Spectrometer image with an unprecedented signal-to-noise ratio (mean S/N $\simeq \sqrt{S} \sim$ 6; maximum S/N > 35). We search within the remnant, using the source detection software wavdetect, for point sources which may indicate a compact object. Despite finding numerous detections of high significance in both broad and narrowband images of the remnant, we are unable to satisfactorily distinguish whether these detections correspond to emission from a compact object. We also present upper limits to the luminosity of an obscured compact stellar object which were derived from an analysis of spectra extracted from the high signal-to-noise image. We are able to further constrain the characteristics of a potential neutron star for this remnant with the results of the analysis presented here, though we cannot confirm the existence of such an object for this remnant.

We present deep high-angular resolution observations of the high-mass protostar NGC 7538 S, which is in the center of a cold dense cloud core with a radius of 0.5 pc and a mass of ∼2000 M_☉. These observations show that NGC 7538 S is embedded in a compact elliptical core with a mass of 85–115 M_☉. The star is surrounded by a rotating accretion disk, which powers a very young, hot molecular outflow approximately perpendicular to the rotating accretion disk. The accretion rate is very high, ∼(1.4–2.8) × 10⁻³ M_☉ yr⁻¹. Evidence for rotation of the disk surrounding the star is seen in all largely optically thin molecular tracers, H¹³CN J = 1 → 0, HN¹³C J = 1 → 0, H¹³CO⁺J = 1 → 0, and DCN J = 3 → 2. Many molecules appear to be affected by the hot molecular outflow, including DCN and H¹³CO⁺. The emission from CH₃CN, which has often been used to trace disk rotation in young high-mass stars, is dominated by the outflow, especially at higher K levels. Our new high angular resolution observations show that the rotationally supported part of the disk is smaller than we previously estimated. The enclosed mass of the inner, rotationally supported part of the disk (D ∼ 5'', i.e., 14,000 AU) is ∼14–24 M_☉.

We report results from a deep high-frequency search for pulsars within the central parsec of Sgr A* using the Green Bank Telescope. The observing frequency of 15 GHz was chosen to maximize the likelihood of detecting normal pulsars (i.e., with periods of ∼500 ms and spectral indices of ∼−1.7) close to Sgr A* that might be used as probes of gravity in the strong-field regime; this is the highest frequency used for such pulsar searches of the Galactic center (GC) to date. No convincing candidate was detected in the survey, with a 10σ detection threshold of ∼10 μJy achieved in two separate observing sessions. This survey represents a significant improvement over previous searches for pulsars at the GC and would have detected a significant fraction (≳5%) of the pulsars around Sgr A*, if they had properties similar to those of the known population. Using our best current knowledge of the properties of the Galactic pulsar population and the scattering material toward Sgr A*, we estimate an upper limit of 90 normal pulsars in orbit within the central parsec of Sgr A*.

Fe K line fluorescence is commonly observed in the X-ray spectra of many X-ray binaries (XRBs) and represents a fundamental tool to investigate the material surrounding the X-ray source. In this paper, we present a comprehensive survey of 41 XRBs (10 HMXBs and 31 LMXBs) with Chandra with specific emphasis on the Fe K region and the narrow Fe Kα line, at the highest resolution possible. We find that (1) the Fe Kα line is always centered at λ = 1.9387 ± 0.0016 Å, compatible with Fe i up to Fe x; we detect no shifts to higher ionization states nor any difference between high mass X-ray binaries (HMXBs) and low mass X-ray binaries (LMXBs). (2) The line is very narrow, with FWHM ⩽ 5 mÅ, normally not resolved by Chandra which means that the reprocessing material is not rotating at high speeds. (3) Fe Kα fluorescence is present in all the HMXBs in the survey. In contrast, such emissions are astonishingly rare (∼10%) among LMXBs where only a few out of a large number showed Fe K fluorescence. However, the line and edge properties of these few are very similar to their high mass cousins. (4) The lack of Fe line emission is always accompanied by the lack of any detectable K edge. (5) We obtain the empirical curve of growth of the equivalent width of the Fe Kα line versus the density column of the reprocessing material, i.e., EW_Kα versus N_H, and show that it is consistent with a reprocessing region spherically distributed around the compact object. (6) We show that fluorescence in XRBs follows the X-ray Baldwin effect as previously only found in the X-ray spectra of active galactic nuclei. We interpret this finding as evidence of decreasing neutral Fe abundance with increasing X-ray illumination and use it to explain some spectral states of Cyg X-1 as a possible cause of the lack of narrow Fe line emission in LMXBs. (7) Finally, we study anomalous morphologies such as Compton shoulders and asymmetric line profiles associated with the line fluorescence. Specifically, we present the first evidence of a Compton shoulder in the HMXB X1908+075. Also, the Fe Kα lines of 4U1700−37 and LMC X-4 present asymmetric wings, suggesting the presence of highly structured stellar winds in these systems.

A new method for the full nonlinear computation of turbulent field lines is presented that extends the Sums of Random Numbers Distribution method previously applied to the computation of generalized quasilinear (GQL) field lines. A study of the mean cross-field displacement confirms the theoretical prediction of a nonlinear diffusion regime, on the large scales where the mean cross-field displacement exceeds twice the perpendicular correlation length. The simulation results duplicate at all length scales the variations of the mean cross-field displacement predicted by the theoretical calculations, including the transitions from GQL supradiffusion to nonlinear diffusion. Both GQL and full nonlinear computations also reproduce, accurately, the predicted variations with turbulence level of the large-scale GQL and nonlinear diffusion coefficients, respectively.

We discuss a model of Poynting-dominated gamma-ray bursts from the collapse of very massive first generation (Pop. III) stars. From redshifts of order 20, the resulting relativistic jets would radiate in the hard X-ray range around 50 keV and above, followed after roughly a day by an external shock component peaking around a few keV. On the same timescales an inverse Compton component around 75 GeV may be expected, as well as a possible infrared flash. The fluences of these components would be above the threshold for detectors such as Swift and Fermi, providing potentially valuable information on the formation and properties of what may be the first luminous objects and their black holes in the high redshift universe.

We use deep V-band surface photometry of five of the brightest elliptical galaxies in the Virgo Cluster to search for diffuse tidal streams, shells, and plumes in their outer halos (r>50 kpc). We fit and subtract elliptical isophotal models from the galaxy images to reveal a variety of substructure, with surface brightnesses in the range μ_V = 26–29 mag arcsec⁻². M49 possesses an extended, interleaved shell system reminiscent of the radial accretion of a satellite companion, while M89's complex system of shells and plumes suggests a more complicated accretion history involving either multiple events or a major merger. M87 has a set of long streamers as might be expected from stripping of low luminosity dwarfs on radial orbits in Virgo. M86 also displays a number of small streams indicative of stripping of dwarf companions, but these comprise much less luminosity than those of M87. Only M84 lacks significant tidal features. We quantify the photometric properties of these structures, and discuss their origins in the context of each galaxy's environment and kinematics within the Virgo Cluster.

We present samples of starburst galaxies that represent the extremes discovered with infrared and ultraviolet observations, including 25 Markarian galaxies, 23 ultraviolet-luminous galaxies discovered with GALEX, and the 50 starburst galaxies having the largest infrared/ultraviolet ratios. These sources have z < 0.5 and cover a luminosity range of ∼10⁴. Comparisons between infrared luminosities determined with the 7.7 μm polycyclic aromatic hydrocarbon feature and ultraviolet luminosities from the stellar continuum at 153 nm are used to determine obscuration in starbursts and dependence of this obscuration on infrared or ultraviolet luminosity. A strong selection effect arises for the ultraviolet-selected samples: the brightest sources appear bright because they have the least obscuration. Obscuration correction for the ultraviolet-selected Markarian+GALEX sample has the form log[UV(intrinsic)/UV(observed)] = 0.07(±0.04)M(UV) + 2.09 ± 0.69 but for the full infrared-selected Spitzer sample is log[UV(intrinsic)/UV(observed)] = 0.17(±0.02)M(UV) + 4.55 ± 0.4. The relation of total bolometric luminosity L_ir to M(UV) is also determined for infrared-selected and ultraviolet-selected samples. For ultraviolet-selected galaxies, log L_ir = −(0.33 ± 0.04)M(UV) + 4.52 ± 0.69. For the full infrared-selected sample, log L_ir = −(0.23 ± 0.02)M(UV) + 6.99 ± 0.41, all for L_ir in L_☉ and M(UV) the AB magnitude at rest frame 153 nm. These results imply that obscuration corrections by factors of 2–3 determined from reddening of the ultraviolet continuum for Lyman break galaxies with z>2 are insufficient, and should be at least a factor of 10 for M(UV) ∼ −17, with decreasing correction for more luminous sources.

Numerical-relativity simulations indicate that the black hole produced in a binary merger can recoil with a velocity up to v_max ≃ 4000 km s⁻¹ with respect to the center of mass of the initial binary. This challenges the paradigm that most galaxies form through hierarchical mergers, yet retain supermassive black holes (SBHs) at their centers despite having escape velocities much less than v_max. Interaction with a circumbinary disk can align the binary black hole spins with their orbital angular momentum, reducing the recoil velocity of the final black hole produced in the subsequent merger. However, the effectiveness of this alignment depends on highly uncertain accretion flows near the binary black holes. In this paper, we show that if the spin S₁ of the more massive binary black hole is even partially aligned with the orbital angular momentum L, relativistic spin precession on sub-parsec scales can align the binary black hole spins with each other. This alignment significantly reduces the recoil velocity even in the absence of gas. For example, if the angle between S₁ and L at large separations is 10° while the second spin S₂ is isotropically distributed, the spin alignment discussed in this paper reduces the median recoil from 864 km s⁻¹ to 273 km s⁻¹ for maximally spinning black holes with a mass ratio of 9/11. This reduction will greatly increase the fraction of galaxies retaining their SBHs.

We have used the Extreme Ultraviolet Imaging Spectrometer on the Hinode spacecraft to observe large areas of outflow near an active region. These outflows are seen to persist for at least 6 days. The emission line profiles suggest that the outflow region is composed of multiple outflowing components, Doppler-shifted with respect to each other. We have modeled this scenario by imposing a double-Gaussian fit to the line profiles. These fits represent the profile markedly better than a single-Gaussian fit for Fe xii and xiii emission lines. For the fastest outflowing components, we find velocities as high as 200 km s⁻¹. However, there remains a correlation between the fitted line velocities and widths, suggesting that the outflows are not fully resolved by the double-Gaussian fit and that the outflow may be comprised of further components.

We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z ⩽ 0.17 and 27 SN events in 492 maxBCG clusters at 0.1 ⩽ z ⩽ 0.3. We find values for the cluster SN Ia rate of (0.37^+0.17+0.01_{−0.12−0.01}) SNurh² and (0.55^+0.13+0.02_{−0.11−0.01}) SNurh² (SNux = 10⁻¹²L⁻¹_x☉ yr⁻¹) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be (0.31^+0.18+0.01_{−0.12−0.01}) SNurh² and (0.49^+0.15+0.02_{−0.11−0.01}) SNurh² in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be (2.04^+1.99+0.07_{−1.11−0.04}) SNurh² and (0.36^+0.84+0.01_{−0.30−0.01}) SNurh² in C4 and maxBCG clusters, respectively. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SN Ia rate in field early-type galaxies is 1.94^+1.31+0.043_{−0.91−0.015} and 3.02^+1.31+0.062_{−1.03−0.048}, for C4 and maxBCG clusters, respectively. The SN rate in galaxy clusters as a function of redshift, which probes the late time SN Ia delay distribution, shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find r_L= [(0.49^+0.15_−0.14)+(0.91^+0.85_−0.81) × z] SNuBh². A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies. With an observation of at most three hostless, intra-cluster SNe Ia, we estimate the fraction of cluster SNe that are hostless to be (9.4^+8.3_−5.1)%.

A significant fraction of the mature FGK stars have cool dusty disks at least an order of magnitude brighter than the solar system's outer zodiacal light. Since such dusts must be continually replenished, they are generally assumed to be the collisional fragments of residual planetesimals analogous to the Kuiper-Belt objects. At least 10% of solar-type stars also bear gas giant planets. The fraction of stars with known gas giants or detectable debris disks (or both) appears to increase with the stellar mass. Here, we examine the dynamical evolution of systems of long-period gas giant planets and residual planetesimals as their host stars evolve off the main sequence, lose mass, and form planetary nebula around remnant white dwarf cores. The orbits of distant gas giant planets and super-km-size planetesimals expand adiabatically. During the most intense asymptotic giant branch mass-loss phase, sub-meter-size particles migrate toward their host stars due to the strong hydrodynamical drag by the intense stellar wind. Along their migration paths, gas giant planets capture and sweep up sub-km-size planetesimals onto their mean-motion resonances. These planetesimals also acquire modest eccentricities which are determined by the mass of the perturbing planets, and the rate and speed of stellar mass loss. The swept-up planetesimals undergo disruptive collisions which lead to the production of grains with an extended size range. The radiation drag on these particles is ineffective against the planets' resonant barrier and they form 30–50 AU size rings which can effectively reprocess the stellar irradiation in the form of FIR continuum. We identify the recently discovered dust ring around the white dwarf WD 2226-210 at the center of the Helix nebula as a prototype of such disks and suggest such rings may be common.

Extrasolar planet host stars have been found to be enriched in key planet-building elements. These enrichments have the potential to drastically alter the composition of material available for terrestrial planet formation. Here, we report on the combination of dynamical models of late-stage terrestrial planet formation within known extrasolar planetary systems with chemical equilibrium models of the composition of solid material within the disk. This allows us to determine the bulk elemental composition of simulated extrasolar terrestrial planets. A wide variety of resulting planetary compositions are found, ranging from those that are essentially "Earth like," containing metallic Fe and Mg silicates, to those that are dominated by graphite and SiC. This shows that a diverse range of terrestrial planets may exist within extrasolar planetary systems.

In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-peaked-spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the expanding lobes, and photoionized by the active nucleus, are responsible for the radio spectral turnover through free–free absorption (FFA) of the synchrotron photons. The model provides a description of the evolution of the spectral energy distribution (SED) of GPS sources with their expansion, predicting significant and complex high-energy emission, from the X-ray to the γ-ray frequency domain. Here, we test this model with the broadband SEDs of a sample of 11 X-ray-emitting GPS galaxies with compact-symmetric-object morphology, and show that (1) the shape of the radio continuum at frequencies lower than the spectral turnover is indeed well accounted for by the FFA mechanism and (2) the observed X-ray spectra can be interpreted as non-thermal radiation produced via IC scattering of the local radiation fields off the lobe particles, providing a viable alternative to the thermal, accretion-disk-dominated scenario. We also show that the relation between the hydrogen column densities derived from the X-ray (N_H) and radio (N_H i) data of the sources is suggestive of a positive correlation, which, if confirmed by future observations, would provide further support to our scenario of high-energy emitting lobes.

A new link in the causal mapping between massive stars and potentially fatal explosive transients opened with the 2008 discovery of the dust-obscured progenitors of the luminous outbursts in NGC 6946 and NGC 300. Here, we carry out a systematic mid-IR photometric search for massive, luminous, and self-obscured stars in four nearby galaxies: M33, NGC 300, M81, and NGC 6946. For detection, we use only the 3.6 μm and 4.5 μm IRAC bands, as these can still be used for multi-epoch Spitzer surveys of nearby galaxies (≲10 Mpc). We combine familiar point-spread function and aperture photometry with an innovative application of image subtraction to catalog the self-obscured massive stars in these galaxies. In particular, we verify that stars analogous to the progenitors of the NGC 6946 (SN 2008S) and NGC 300 transients are truly rare in all four galaxies: their number may be as low as ∼1 per galaxy at any given moment. This result empirically supports the idea that the dust-enshrouded phase is a very short lived phenomenon in the lives of many massive stars and that these objects constitute a natural extension of the asymptotic giant branch sequence. We also provide mid-IR catalogs of sources in NGC 300, M81, and NGC 6946.

The recent Voyager 2 (V2) observations of the termination shock (TS) indicate that it is a plasma shock unlike any other in the heliosphere with the dynamics and structure heavily influenced by the presence of an energized population of pickup ions (PUIs). The "unexpected" finding of cold plasma downstream of the TS in the heliosheath, corresponding to very little heating of the thermal solar wind (SW), suggests that the energy dissipated by the shock is dominated by the energization of PUIs at the TS. We examine the "shock surfing" mechanism at the test particle level, where multiply reflected ions (MRIs) gain energy from the motional electric field as a consequence of reflection from the cross-shock potential (CSP), for a model of the TS3 (the third TS crossing measured by V2). The energization of PUI filled-shell distributions at a stationary, perpendicular model of the TS3 indicates that shock surfing can provide both substantial PUI acceleration and a dissipation mechanism at the TS. For a sufficiently strong CSP and sufficiently narrow shock ramp MRI acceleration can account for the "missing" energy of the downstream SW plasma.

Coincident detections of electromagnetic (EM) and gravitational wave (GW) signatures from coalescence events of supermassive black holes (SMBHs) are the next observational grand challenge. Such detections will provide the means to study cosmological evolution and accretion processes associated with these gargantuan compact objects. More generally, the observations will enable testing general relativity in the strong, nonlinear regime and will provide independent cosmological measurements to high precision. Understanding the conditions under which coincidences of EM and GW signatures arise during SMBH mergers is therefore of paramount importance. As an essential step toward this goal, we present results from the first fully general relativistic, hydrodynamical study of the late inspiral and merger of equal-mass, spinning SMBH binaries in a gas cloud. We find that variable EM signatures correlated with GWs can arise in merging systems as a consequence of shocks and accretion combined with the effect of relativistic beaming. The most striking EM variability is observed for systems where spins are aligned with the orbital axis and where orbiting black holes form a stable set of density wakes, but all systems exhibit some characteristic signatures that can be utilized in searches for EM counterparts. In the case of the most massive binaries observable by the Laser Interferometer Space Antenna, calculated luminosities imply that they may be identified by EM searches to z ≈ 1, while lower mass systems and binaries immersed in low density ambient gas can only be detected in the local universe.

We discuss high angular resolution observations of ammonia toward four candidate high-mass starless cores (HMSCs). The cores were identified by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) during its 2005 survey of the Vulpecula region where 60 compact sources were detected simultaneously at 250, 350, and 500 μm. Four of these cores, with no IRAS–PSC or MSX counterparts, were mapped with the NRAO Very Large Array and observed with the Effelsberg 100 m telescope in the NH₃(1,1) and (2,2) spectral lines. Our observations indicate that the four cores are cold (T_k < 16 K) and show a filamentary and/or clumpy structure. They also show a significant velocity substructure within ∼1 km s⁻¹. The four BLAST cores appear to be colder and more quiescent than other previously observed HMSC candidates, suggesting an earlier stage of evolution.

A3667 is the archetype of a merging cluster with radio relics. The northwest (NW) radio relic is the brightest cluster relic or halo known and is believed to be due to a strong merger shock. We have observed the NW relic for ∼40 ks of net XMM-Newton time. We observe a global decline of temperature across the relic from 6 to 1 keV, similar to the Suzaku results. Our new observations reveal a sharp change of both temperature and surface brightness near the position of the relic. The increased X-ray emission on the relic can be equivalently well described by either a thermal or nonthermal spectral model. The parameters of the thermal model are consistent with a Mach number ${\cal {M}}\sim 2$ shock and a shock speed of ∼1200 km s⁻¹. The energy content of the relativistic particles in the radio relic can be explained if they are (re)-accelerated by the shock with an efficiency of ∼0.2%. Comparing the limit on the inverse Compton X-ray emission with the measured radio synchrotron emission, we set a lower limit to the magnetic field in the relic of 3 μG. If the emission from the relic is nonthermal, this lower limit is in fact the required magnetic field.

We use Bayesian statistics and Markov chain Monte Carlo (MCMC) techniques to construct dynamical models for the spiral galaxy NGC 6503. The constraints include surface brightness (SB) profiles which display a Freeman Type II structure; H i and ionized gas rotation curves; the stellar rotation, which is nearly coincident with the ionized gas curve; and the line of sight stellar dispersion, which displays a σ-drop at the center. The galaxy models consist of a Sérsic bulge, an exponential disk with an optional inner truncation and a cosmologically motivated dark halo. The Bayesian/MCMC technique yields the joint posterior probability distribution function for the input parameters, allowing constraints on model parameters such as the halo cusp strength, structural parameters for the disk and bulge, and mass-to-light ratios. We examine several interpretations of the data: the Type II SB profile may be due to dust extinction, to an inner truncated disk, or to a ring of bright stars, and we test separate fits to the gas and stellar rotation curves to determine if the gas traces the gravitational potential. We test each of these scenarios for bar stability, ruling out dust extinction. We also find that the gas likely does not trace the gravitational potential, since the predicted stellar rotation curve, which includes asymmetric drift, is then inconsistent with the observed stellar rotation curve. The disk is well fit by an inner-truncated profile, but the possibility of ring formation by a bar to reproduce the Type II profile is also a realistic model. We further find that the halo must have a cuspy profile with γ ≳ 1; the bulge has a lower M/L than the disk, suggesting a star-forming component in the center of the galaxy; and the bulge, as expected for this late-type galaxy, has a low Sérsic index with n_b ∼ 1–2, suggesting a formation history dominated by secular evolution.

We present a study on the impact of molecular outflows in the Perseus molecular cloud complex using the COMPLETE Survey large-scale ¹²CO(1–0) and ¹³CO(1–0) maps. We used three-dimensional isosurface models generated in right ascension–declination–velocity space to visualize the maps. This rendering of the molecular line data allowed for a rapid and efficient way to search for molecular outflows over a large (∼16 deg²) area. Our outflow-searching technique detected previously known molecular outflows as well as new candidate outflows. Most of these new outflow-related high-velocity features lie in regions that have been poorly studied before. These new outflow candidates more than double the amount of outflow mass, momentum, and kinetic energy in the Perseus cloud complex. Our results indicate that outflows have significant impact on the environment immediately surrounding localized regions of active star formation, but lack the energy needed to feed the observed turbulence in the entire Perseus complex. This implies that other energy sources, in addition to protostellar outflows, are responsible for turbulence on a global cloud scale in Perseus. We studied the impact of outflows in six regions with active star formation within Perseus of sizes in the range of 1–4 pc. We find that outflows have enough power to maintain the turbulence in these regions and enough momentum to disperse and unbind some mass from them. We found no correlation between outflow strength and star formation efficiency (SFE) for the six different regions we studied, contrary to results of recent numerical simulations. The low fraction of gas that potentially could be ejected due to outflows suggests that additional mechanisms other than cloud dispersal by outflows are needed to explain low SFEs in clusters.

To date, mid-infrared properties of Galactic black hole binaries have barely been investigated in the framework of multi-wavelength campaigns. Yet, studies in this spectral domain are crucial to get complementary information on the presence of dust and/or on the physical processes such as dust heating and thermal bremsstrahlung. Here, we report a long-term multi-wavelength study of the microquasar GRS 1915+105. On the one hand, we aimed at understanding the origins of the mid-infrared emission, and on the other hand, at searching for correlation with the high-energy and/or radio activities. We observed the source at several epochs between 2004 and 2006 with the photometer IRAC and spectrometer IRS, both mounted on the SpitzerSpace Telescope. When available, we completed our set of data with quasi-simultaneous RXTE/INTEGRAL high-energy and/or Ryle radio observations from public archives. We then studied the mid-infrared environment and activities of GRS 1915+105 through spectral analysis and broadband fitting of its radio to X-ray spectral energy distributions. We detected polycyclic aromatic hydrocarbon molecules in all but one IRS spectra of GRS 1915+105 which unambiguously proves the presence of a dust component, likely photoionized by the high-energy emission. We also argue that this dust is distributed in a disk-like structure heated by the companion star, as observed in some Herbig Ae/Be and isolated cool giant stars. Moreover, we show that some of the soft X-ray emission emanating from the inner regions of the accretion disk is reprocessed and thermalized in the outer part. This leads to a mid-infrared excess that is very likely correlated to the soft X-ray emission. We exclude thermal bremsstrahlung as contributing significantly in this spectral domain.

We have used high-cadence radial velocity (RV) measurements from the Hobby-Eberly Telescope with existing velocities from the Lick, Elodie, Harlan J. Smith, and Whipple 60'' telescopes combined with astrometric data from the Hubble Space Telescope Fine Guidance Sensors to refine the orbital parameters and determine the orbital inclinations and position angles of the ascending node of components υ And A c and d. With these inclinations and using M_* = 1.31M_☉ as a primary mass, we determine the actual masses of two of the companions: υ And A c is 13.98^+2.3_−5.3M_JUP, and υ And A d is 10.25^+0.7_−3.3M_JUP. These measurements represent the first astrometric determination of mutual inclination between objects in an extrasolar planetary system, which we find to be 299 ± 1°. The combined RV measurements also reveal a long-period trend indicating a fourth planet in the system. We investigate the dynamic stability of this system and analyze regions of stability, which suggest a probable mass of υ And A b. Finally, our parallaxes confirm that υ And B is a stellar companion of υ And A.

We present a new code, CASTRO, that solves the multicomponent compressible hydrodynamic equations for astrophysical flows including self-gravity, nuclear reactions, and radiation. CASTRO uses an Eulerian grid and incorporates adaptive mesh refinement (AMR). Our approach to AMR uses a nested hierarchy of logically rectangular grids with simultaneous refinement in both space and time. The radiation component of CASTRO will be described in detail in the next paper, Part II, of this series.

We analyze the precursor of a Forbush decrease (FD) observed with the Global Muon Detector Network on 2006 December 14. An intense geomagnetic storm is also recorded during this FD with the peak Kp index of 8+. By using the "two-dimensional map" of the cosmic ray intensity produced after removing the contribution from the diurnal anisotropy, we succeed in extracting clear signatures of the precursor. A striking feature of this event is that a weak loss-cone (LC) signature is first recorded more than a day prior to the storm sudden commencement (SSC) onset. This suggests that the LC precursor appeared only 7 hr after the coronal mass ejection eruption from the Sun, when the interplanetary (IP) shock driven by the interplanetary coronal mass ejection was located at 0.4 AU from the Sun. We find the precursor being successively observed with multiple detectors in the network according to the Earth's spin and confirmed that the precursor continuously exists in space. The long lead time (15.6 hr) of this precursor which is almost twice the typical value indicates that the interplanetary magnetic field (IMF) was more quiet in this event than a typical power spectrum assumed for the IMF turbulence. The amplitude (−6.45%) of the LC anisotropy at the SSC onset is more than twice the FD size, indicating that the maximum intensity depression behind the IP shock is much larger than the FD size recorded at the Earth in this event. We also find the excess intensity from the sunward IMF direction clearly observed during ∼10 hr preceding the SSC onset. It is shown that this excess intensity is consistent with the measurement of the particles accelerated by the head-on collisions with the approaching shock. This is the first detailed observation of the precursor due to the shock reflected particles with muon detectors.

We study the spectral evolution of pulsar wind nebulae (PWNe) taking into account the energy injected when they are young. We model the evolution of the magnetic field inside a uniformly expanding PWN. Considering time-dependent injection from the pulsar and coolings by radiative and adiabatic losses, we solve the evolution of the particle distribution function. The model is calibrated by fitting the calculated spectrum to the observations of the Crab Nebula at an age of a thousand years. The spectral evolution of the Crab Nebula in our model shows that the flux ratio of TeV γ-rays to X-rays increases with time, which implies that old PWNe are faint in X-rays, but not in TeV γ-rays. The increase of this ratio is because the magnetic field decreases with time and is not because the X-ray emitting particles are cooled more rapidly than the TeV γ-ray emitting particles. Our spectral evolution model matches the observed rate of the radio flux decrease of the Crab Nebula. This result implies that our magnetic field evolution model is close to the reality. Finally, from the viewpoint of the spectral evolution, only a small fraction of the injected energy from the Crab Pulsar needs to go to the magnetic field, which is consistent with previous studies.

In 2006 May, comet 73P/Schwassmann–Wachmann 3 experienced large outburst activity allowing us to study the gas production rate of fresh material released from the nucleus. We observed the comet in a coordinated campaign using millimeter and optical facilities at heliocentric distances between 0.966 and 1.033 AU. During this time, we had the opportunity to follow the post-outburst evolution of fragment B, which evidenced larger production rates in comparison to fragment C, the latter showing a rather stable gas production rate (Q_HCN ∼2 × 10²⁵ molecules s⁻¹). In addition to the investigation of the gas evolution, we studied the possible role of HCN and dust as progenitors for the CN radical. From our joint observations on May 12, we observed a high correlation of CN with HCN and low correlation with the continuum emission (grains). Herewith, our study supports the view of HCN as a major source of CN, although the presence of other sources for cyanide cannot be fully ruled out.

Current models of pulsar gamma-ray emission use the magnetic field of a rotating dipole in vacuum as a first approximation to the shape of a plasma-filled pulsar magnetosphere. In this paper, we revisit the question of gamma-ray light curve formation in pulsars in order to ascertain the robustness of the "two-pole caustic (TPC)" and "outer gap (OG)" models based on the vacuum magnetic field. We point out an inconsistency in the literature on the use of the relativistic aberration formula, where in several works the shape of the vacuum field was treated as known in the instantaneous corotating frame, rather than in the laboratory frame. With the corrected formula, we find that the peaks in the light curves predicted from the TPC model using the vacuum field are less sharp. The sharpness of the peaks in the OG model is less affected by this change, but the range of magnetic inclination angles and viewing geometries resulting in double-peaked light curves is reduced. In a realistic magnetosphere, the modification of field structure near the light cylinder (LC) due to plasma effects may change the shape of the polar cap and the location of the emission zones. We study the sensitivity of the light curves to different shapes of the polar cap for static and retarded vacuum dipole fields. In particular, we consider polar caps traced by the last open field lines and compare them to circular polar caps. We find that the TPC model is very sensitive to the shape of the polar cap, and a circular polar cap can lead to four peaks of emission. The OG model is less affected by different polar cap shapes, but is subject to big uncertainties of applying the vacuum field near the LC. We conclude that deviations from the vacuum field can lead to large uncertainties in pulse shapes, and a more realistic force-free field should be applied to the study of pulsar high-energy emission.

Gamma-ray emission from pulsars has long been modeled using a vacuum dipole field. This approximation ignores changes in the field structure caused by the magnetospheric plasma and strong plasma currents. We present the first results of gamma-ray pulsar light-curve modeling using the more realistic field taken from three-dimensional force-free (FF) magnetospheric simulations. Having the geometry of the field, we apply several prescriptions for the location of the emission zone, comparing the light curves to observations. We find that when the emission region is chosen according to the conventional slot-gap (or two-pole caustic) prescription, the model fails to produce double-peak pulse profiles, mainly because the size of the polar cap in the FF magnetosphere is larger than the vacuum field polar cap. This suppresses caustic formation in the inner magnetosphere. The conventional outer-gap model is capable of producing only one peak under general conditions because a large fraction of open field lines does not cross the null charge surface. We propose a novel "separatrix layer" model, where the high-energy emission originates from a thin layer on the open field lines just inside of the separatrix that bounds the open flux tube. The emission from this layer generates two strong caustics on the sky map due to the effect we term "Sky Map Stagnation" (SMS). It is related to the fact that the FF field asymptotically approaches the field of a rotating split monopole, and the photons emitted on such field lines in the outer magnetosphere arrive to the observer in phase. The double-peak light curve is a natural consequence of SMS. We show that most features of the currently available gamma-ray pulsar light curves can be reasonably well reproduced and explained with the separatrix layer model using the FF field. Association of the emission region with the current sheet will guide more detailed future studies of the magnetospheric acceleration physics.

We numerically investigate the effect of feedback from the ionization heating from massive stars on the evolution of giant molecular clouds (GMCs) and their star formation efficiency (SFE), which we treat as an instantaneous, time-dependent quantity. We follow the GMCs' evolution from their formation to advanced star-forming stages. After an initial period of contraction, the collapsing clouds begin forming stars, whose feedback evaporates part of the clouds' mass, opposing the continuing accretion from the infalling gas. Our results are as follows: (1) in the presence of feedback, the clouds attain levels of the SFE that are consistent at all times with observational determinations for regions of comparable star formation rates. (2) However, the dense gas mass is larger in general in the presence of feedback, while the total mass (dense gas + stars) is nearly insensitive to the presence of feedback, suggesting that it is determined mainly by the accretion, while the feedback inhibits mainly the conversion of dense gas to stars, because it acts directly to reheat and disperse the gas that is directly on its way to forming stars. (3) The factor by which the SFE is reduced upon the inclusion of feedback is a decreasing function of the cloud's mass, for clouds of size ∼10 pc. This naturally explains the larger observed SFEs of massive-star-forming regions. (4) The clouds may attain a pseudo-virialized state, with a value of the virial mass very similar to the actual cloud mass. However, this state differs from true virialization in that the clouds, rather than being equilibrium entities, are the centers of a larger-scale collapse, in which accretion replenishes the mass consumed by star formation. (5) The higher-density regions within the clouds are in a similar situation, accreting gas infalling from the less-dense, more extended regions of the clouds. (6) The density probability density functions of the regions containing the clouds in general exhibit a shape characteristic of thermally bistable flows, and extend down to densities corresponding to the warm atomic medium, because the warm gas interpenetrates the clouds. The general picture arising from our simulations is that the gas involved in the gravitational contraction leading to star formation extends to large scales and is not confined to the local environment of the final collapse, where the effect of the feedback is active, in agreement with recent proposals of a gravitationally driven mass cascade from large to small scales.

We discuss outer gap closure mechanism in the trans-field direction with the magnetic pair-creation process near the stellar surface. The gap closure by the magnetic pair creation is possible if some fraction of the pairs are produced with an outgoing momentum. By assuming that multiple magnetic field will affect the local field near the stellar surface, we show a specific magnetic field geometry near the stellar surface resulting in the outflow of the pairs. Together with the fact that the electric field is weak below null charge surface, the characteristic curvature photon energy emitted by incoming particles, which were accelerated in the outer gap, decreases drastically to ∼100 MeV near the stellar surface. We estimate the height measured from the last-open field line, above which 100 MeV photons are converted into pairs by the magnetic pair creation. We also show the resultant multiplicity due to the magnetic pair-creation process could acquire $M_{e^{\pm }}\sim 10^4\hbox{--}10^5$. In this model, the fractional outer gap size is proportional to P^−1/2. The predicted γ-ray luminosity (L_γ) and the characteristic curvature photon energy (E_c) emitted from the outer gap are proportional to B²P^−5/2 and B^3/4P⁻¹, respectively. This model also predicts that L_γ and E_c are related to the spin-down power (L_sd) or the spin-down age of pulsars (τ) as L_γ ∝ L^5/8_sd or L_γ ∝ τ^−5/4 and E_c ∝ L^1/4_sd or E_c ∝ τ^−1/2, respectively.

We present first results of a Chandra X-ray observation of the rare oxygen-type Wolf–Rayet (WR) star WR 142 (= Sand 5 = St 3) harbored in the young, heavily obscured cluster Berkeley 87. Oxygen-type WO stars are thought to be the most evolved of the WRs and progenitors of supernovae or gamma-ray bursts. As part of an X-ray survey of supposedly single WR stars, we observed WR 142 and the surrounding Berkeley 87 region with Chandra ACIS-I. We detect WR 142 as a faint yet extremely hard X-ray source. Due to weak emission, its nature as a thermal or non-thermal emitter is unclear and thus we discuss several emission mechanisms. Additionally, we report seven detections and eight non-detections by Chandra of massive OB stars in Berkeley 87, two of which are bright yet soft X-ray sources whose spectra provide a dramatic contrast to the hard emission from WR 142.

SN 2007if was the third over-luminous Type Ia supernova (SN Ia) detected after 2003fg and 2006gz. We present the photometric and spectroscopic observations of the SN and its host by ROTSE-III, HET, and Keck. From the H_α line identified in the host spectra, we determine a redshift of 0.0736. At this distance, the SN reached an absolute magnitude of −20.4, brighter than any other SNe Ia ever observed. If the source of luminosity is radioactive decay, a large amount of radioactive nickel (∼1.5 M_☉) is required to power the peak luminosity, more than can be produced realistically in a Chandrasekhar mass progenitor. Low expansion velocity, similar to that of 2003fg, is also measured around the maximum light. The observations may suggest that SN 2007if was from a massive white dwarf progenitor, plausibly exploding with mass well beyond 1.4 M_☉. Alternatively, we investigate circumstellar interaction that may contribute to the excess luminosity.

Intermediate between the prestellar and Class 0 protostellar phases, the first core is a quasi-equilibrium hydrostatic object with a short lifetime and an extremely low luminosity. Recent magnetohydrodynamic (MHD) simulations suggest that the first core can even drive a molecular outflow before the formation of the second core (i.e., protostar). Using the Submillimeter Array and the Spitzer Space Telescope, we present high angular resolution observations toward the embedded dense core IRS2E in L1448. We find that source L1448 IRS2E is not visible in the sensitive Spitzer infrared images (at wavelengths from 3.6 to 70 μm) and has weak (sub-) millimeter dust continuum emission. Consequently, this source has an extremely low bolometric luminosity (<0.1 L_☉). Infrared and (sub-) millimeter observations clearly show an outflow emanating from this source; L1448 IRS2E represents thus far the lowest luminosity source known to be driving a molecular outflow. Comparisons with prestellar cores and Class 0 protostars suggest that L1448 IRS2E is more evolved than prestellar cores but less evolved than Class 0 protostars, i.e., at a stage intermediate between prestellar cores and Class 0 protostars. All these results are consistent with the theoretical predictions of the radiative/MHD simulations, making L1448 IRS2E the most promising candidate of the first hydrostatic core revealed so far.

We present results derived from a dual-spacecraft tomographic reconstruction of the solar corona's three-dimensional (3D) extreme ultraviolet (EUV) emissivity. We use simultaneously taken STEREO A and B spacecraft EUVI images from Carrington rotation 2077 (UT 2008 November 20 06:56 through UT December 17 14:34). During this period, the spacecraft view angles were separated by an average 854 which allowed for the reconstruction to be performed with data gathered in about 3/4 of a full solar rotational time. The EUV reconstructions provide the 3D emissivity in each of the three EUVI Fe bands, in the range of heights 1.00–1.25 R_s. We use this information to perform local differential emission measure (LDEM) analysis. Taking moments of the so-derived LDEM distributions gives the 3D values of the electron density, temperature, and temperature spread. We determine relationships between the moments of the LDEM and the coronal magnetic field by making longitudinal averages of the moments, and relating them to the global-scale structures of a potential field source surface magnetic field model. In this way, we determine how the electron density, mean temperature, and temperature spread vary for different coronal structures. We draw conclusions about the relationship between the LDEM moments and the sources of the fast and slow solar winds, and the transition between the two regimes.

High-resolution spectroscopy in the near-infrared could become the leading method for discovering extra-solar planets around very low mass stars and brown dwarfs. In order to help to achieve an accuracy of ∼m s⁻¹, we are developing a gas cell which consists of a mixture of gases whose absorption spectral lines span all over the near-infrared region. We present the most promising mixture, made of acetylene, nitrous oxide, ammonia, chloromethanes, and hydrocarbons. The mixture is contained in a small size 13 cm long gas cell and covers most of the H and K bands. It also shows small absorptions in the J band, but they are few and not sharp enough for near-infrared wavelength calibration. We describe the working method and experiments, and compare our results with the state of the art for near-infrared gas cells.

We report Spitzer Space Telescope observations of the four lowest rotational transitions of H₂ in three portions of the boundary of the Taurus molecular cloud. Emission in the two lowest transitions, S(0) and S(1), was detected in almost all pointing directions, while the S(2) and S(3) lines were marginally detected only after further averaging of data. The widespread detection of lines coming from levels 510 K and 1016 K above the molecular ground state is indicative of gas at a temperature of at least 200 K containing column densities (1–5) × 10¹⁸ cm⁻² of H₂. For the region with the simplest geometry, we have used the Meudon PDR code to model the chemistry, radiative transfer, and excitation of molecular hydrogen. We conclude that models with acceptable values of the UV interstellar radiation field can reproduce the amount of H₂ in the lowest excited state, but cannot account for the degree of excitation of the H₂. The unexpectedly high degree of excitation of the H₂ in the boundary layer of a molecular cloud, which cannot be explained by the presence of stellar sources, points to an enhanced heating rate which may be the result of, e.g., dissipation of turbulence. We have in one boundary region been able to obtain the ortho-to-para ratio (OPR) for H₂, which by modeling and possible detection of the S(2) and S(3) lines has a range 1.0 ⩾ OPR ⩾ 0.15, although this result must be treated with caution. The fact that the ortho-to-para ratio is lower than that expected for equilibrium at the gas kinetic temperature may be indicative of circulation of material from cold, purely molecular regions into the boundary layer, possibly due to turbulent diffusion. The explanation of these data may thus be suggestive of processes that are having a significant effect on the structure and evolution of molecular clouds and the star formation that takes place within them.

We evaluate two dominant nuclear reaction rates and their uncertainties that affect ⁴⁴Ti production in explosive nucleosynthesis. Experimentally we develop thick target yields for the ⁴⁰Ca(α, γ)⁴⁴Ti reaction at E_α = 4.13, 4.54, and 5.36 MeV using γ-ray spectroscopy. At the highest beam energy, we also performed an activation measurement which agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower ⁴⁴Ti production in scenarios for the α-rich freezeout. Special attention has been paid to assessing realistic uncertainties of stellar reaction rates produced from a combination of experimental and theoretical cross sections. With such methods, we also develop a re-evaluation of the ⁴⁴Ti(α, p)⁴⁷V reaction rate. Using these two rates we carry out a sensitivity survey of ⁴⁴Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in ⁴⁴Ti synthesis as that produced by different treatments of stellar physics.

We present measurements of the relative abundances of cosmic-ray nuclei in the energy range of 500–3980 GeV/nucleon from the second flight of the Cosmic Ray Energetics And Mass balloon-borne experiment. Particle energy was determined using a sampling tungsten/scintillating-fiber calorimeter, while particle charge was identified precisely with a dual-layer silicon charge detector installed for this flight. The resulting element ratios C/O, N/O, Ne/O, Mg/O, Si/O, and Fe/O at the top of atmosphere are 0.919 ± 0.123^stat ± 0.030^syst, 0.076 ± 0.019^stat ± 0.013^syst, 0.115 ± 0.031^stat ± 0.004^syst, 0.153 ± 0.039^stat ± 0.005^syst, 0.180 ± 0.045^stat ± 0.006^syst, and 0.139 ± 0.043^stat ± 0.005^syst, respectively, which agree with measurements at lower energies. The source abundance of N/O is found to be 0.054 ± 0.013^stat ± 0.009^{syst+0.010esc}_−0.017. The cosmic-ray source abundances are compared to local Galactic (LG) abundances as a function of first ionization potential and as a function of condensation temperature. At high energies the trend that the cosmic-ray source abundances at large ionization potential or low condensation temperature are suppressed compared to their LG abundances continues. Therefore, the injection mechanism must be the same at TeV/nucleon energies as at the lower energies measured by HEAO-3, CRN, and TRACER. Furthermore, the cosmic-ray source abundances are compared to a mixture of 80% solar system abundances and 20% massive stellar outflow (MSO) as a function of atomic mass. The good agreement with TIGER measurements at lower energies confirms the existence of a substantial fraction of MSO material required in the ∼TeV per nucleon region.

We report unusual near- and mid-infrared photometric properties of G 196–3 B, the young substellar companion at 16'' from the active M2.5-type star G 196–3 A, using data taken with the IRAC and MIPS instruments onboard Spitzer. G 196–3 B shows markedly redder colors at all wavelengths from 1.6 up to 24 μm than expected for its spectral type, which is determined at L3 from optical and near-infrared spectra. We discuss various physical scenarios to account for its reddish nature and conclude that a low-gravity atmosphere with enshrouded upper atmospheric layers and/or a warm dusty disk/envelope provides the most likely explanations, the two of them consistent with an age in the interval 20–300 Myr. We also present new and accurate separate proper motion measurements for G 196–3 A and B confirming that both objects are gravitationally linked and share the same motion within a few mas yr⁻¹. After integration of the combined spectrophotometric spectral energy distributions, we obtain the result that the difference in the bolometric magnitudes of G 196–3 A and B is 6.15 ± 0.10 mag. Kinematic consideration of the Galactic space motions of the system for distances in the interval 15–30 pc suggests that the pair is a likely member of the Local Association and that it lies near the past positions of young star clusters like α Persei less than 85 Myr ago, where the binary might have originated. At these young ages, the mass of G 196–3 B would be in the range 12–25 M_Jup, close to the frontier between planets and brown dwarfs.

We measure the half-light radii of globular clusters (GCs) in 43 galaxies from the Advanced Camera for Surveys (ACS) Fornax Cluster Survey. We use these data to extend previous work in which the environmental dependencies of the half-light radii of GCs in early-type galaxies in the ACS Virgo Cluster Survey were studied, and a corrected mean half-light radius (corrected for the observed environmental trends) was suggested as a reliable distance indicator. This work both increases the sample size for the study of the environmental dependencies, and adds leverage to the study of the corrected half-light radius as a possible distance indicator (since Fornax lies at a larger distance than the Virgo cluster). We study the environmental dependencies of the size of GCs using both a Principal Component Analysis as well as two-dimensional scaling relations. We largely confirm the environmental dependencies shown in Jordán et al., but find evidence that there is a residual correlation in the mean half-light radius of GC systems with galaxy magnitude, and subtle differences in the other correlations—so there may not be a universal correction for the half-light radii of lower luminosity galaxy GC systems. The main factor determining the size of a GC in an early-type galaxy is the GC color. Red GCs have 〈r_h〉 = 2.8 ± 0.3 pc, while blue GCs have 〈r_h〉 = 3.4 ± 0.3 pc. We show that for bright early-type galaxies (M_B < −19 mag), the uncorrected mean half-light radius of the GC system is by itself an excellent distance indicator (with error ∼11%), having the potential to reach cosmologically interesting distances in the era of high angular resolution adaptive optics on large optical telescopes.

We present the results of a search for gravitational-wave bursts (GWBs) associated with 137 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments during the fifth LIGO science run and first Virgo science run. The data used in this analysis were collected from 2005 November 4 to 2007 October 1, and most of the GRB triggers were from the Swift satellite. The search uses a coherent network analysis method that takes into account the different locations and orientations of the interferometers at the three LIGO–Virgo sites. We find no evidence for GWB signals associated with this sample of GRBs. Using simulated short-duration (<1 s) waveforms, we set upper limits on the amplitude of gravitational waves associated with each GRB. We also place lower bounds on the distance to each GRB under the assumption of a fixed energy emission in gravitational waves, with a median limit of D ∼ 12 Mpc(E^iso_GW/0.01 M_☉c²)^1/2 for emission at frequencies around 150 Hz, where the LIGO–Virgo detector network has best sensitivity. We present astrophysical interpretations and implications of these results, and prospects for corresponding searches during future LIGO–Virgo runs.

Progenitor scenarios for short gamma-ray bursts (short GRBs) include coalescenses of two neutron stars or a neutron star and black hole, which would necessarily be accompanied by the emission of strong gravitational waves. We present a search for these known gravitational-wave signatures in temporal and directional coincidence with 22 GRBs that had sufficient gravitational-wave data available in multiple instruments during LIGO's fifth science run, S5, and Virgo's first science run, VSR1. We find no statistically significant gravitational-wave candidates within a [ − 5, + 1) s window around the trigger time of any GRB. Using the Wilcoxon–Mann–Whitney U-test, we find no evidence for an excess of weak gravitational-wave signals in our sample of GRBs. We exclude neutron star–black hole progenitors to a median 90% confidence exclusion distance of 6.7  Mpc.

Observations continue to support the interpretation of the anomalous microwave foreground as electric dipole radiation from spinning dust grains as proposed by Draine & Lazarian. In this paper, we present a refinement of the original model by improving the treatment of a number of physical effects. First, we consider a disk-like grain rotating with angular velocity at an arbitrary angle with respect to the grain symmetry axis (i.e., grain wobbling) and derive the rotational damping and excitation coefficients arising from infrared emission, plasma–grain interactions, and electric dipole emission. The angular velocity distribution and the electric dipole emission spectrum for disk-like grains is calculated using the Langevin equation, for cases both with and without fast internal relaxation. Our results show that for fast internal relaxation, the peak emissivity of spinning dust, compared to earlier studies, increases by a factor of ∼2 for the warm neutral medium (WNM), the warm ionized medium (WIM), the cold neutral medium (CNM), and the photodissociation region, and by a factor ∼4 for reflection nebulae. The frequency at the emission peak also increases by factors ∼1.4 to ∼2 for these media. Without internal relaxation, the increase of emissivity is comparable, but the emission spectrum is more extended to higher frequency. The increased emission results from the non-sphericity of grain shape and from the anisotropy in damping and excitation along directions parallel and perpendicular to the grain symmetry axis. Second, we provide a detailed numerical study including transient spin-up of grains by single-ion collisions. The range of grain size in which single-ion collisions are important is identified. The impulses broaden the emission spectrum and increase the peak emissivity for the CNM, WNM, and WIM, although the increases are not as large as those due to the grain wobbling. In addition, we present an improved treatment of rotational excitation and damping by infrared emission.

A novel statistic is proposed to examine the hypothesis that all cluster galaxies are drawn from the same luminosity distribution (LD). In such a "statistical model" of galaxy LD, the brightest cluster galaxies (BCGs) are simply the statistical extreme of the galaxy population. Using a large sample of nearby clusters, we show that BCGs in high luminosity clusters (e.g., L_tot ≳ 4 × 10¹¹h⁻²₇₀ L_☉) are unlikely (probability ⩽3 × 10⁻⁴) to be drawn from the LD defined by all red cluster galaxies more luminous than M_r = −20. On the other hand, BCGs in less luminous clusters are consistent with being the statistical extreme. Applying our method to the second brightest galaxies, we show that they are consistent with being the statistical extreme, which implies that the BCGs are also distinct from non-BCG luminous, red, cluster galaxies. We point out some issues with the interpretation of the classical tests proposed by Tremaine & Richstone (TR) that are designed to examine the statistical nature of BCGs, investigate the robustness of both our statistical test and those of TR against difficulties in photometry of galaxies of large angular size, and discuss the implication of our findings on surveys that use the luminous red galaxies to measure the baryon acoustic oscillation features in the galaxy power spectrum.

Several neutral species (Mg i, Si i, Ca i, Fe i) have been detected in a weak Mg ii absorption line system (W_r(2796) ∼ 0.15 Å) at z ∼ 0.45 along the sightline toward HE0001-2340. These observations require extreme physical conditions, as noted in D'Odorico. We place further constraints on the properties of this system by running a wide grid of photoionization models, determining that the absorbing cloud that produces the neutral absorption is extremely dense (∼100–1000 cm⁻³), cold (<100 K), and has significant molecular content (∼72%–94%). Structures of this size and temperature have been detected in Milky Way CO surveys and have been predicted in hydrodynamic simulations of turbulent gas. In order to explain the observed line profiles in all neutral and singly ionized chemical transitions, the lines must suffer from unresolved saturation and/or the absorber must partially cover the broad emission line region of the background quasar. In addition to this highly unusual cloud, three other ordinary weak Mg ii clouds (within densities of ∼0.005 cm⁻³ and temperatures of ∼10, 000 K) lie within 500 km s⁻¹ along the same sightline. We suggest that the "bare molecular cloud," which appears to reside outside of a galaxy disk, may have had in situ star formation and may evolve into an ordinary weak Mg ii absorbing cloud.

The joint likelihood of observable cluster signals reflects the astrophysical evolution of the coupled baryonic and dark matter components in massive halos, and its knowledge will enhance cosmological parameter constraints in the coming era of large, multiwavelength cluster surveys. We present a computational study of intrinsic covariance in cluster properties using halo populations derived from Millennium Gas Simulations (MGS). The MGS are re-simulations of the original 500 h⁻¹ Mpc Millennium Simulation performed with gas dynamics under two different physical treatments: shock heating driven by gravity only (GO) and a second treatment with cooling and preheating (PH). We examine relationships among structural properties and observable X-ray and Sunyaev–Zel'dovich (SZ) signals for samples of thousands of halos with M₂₀₀ ⩾ 5 × 10¹³ h⁻¹ M_☉ and z < 2. While the X-ray scaling behavior of PH model halos at low redshift offers a good match to local clusters, the model exhibits non-standard features testable with larger surveys, including weakly running slopes in hot gas observable–mass relations and ∼10% departures from self-similar redshift evolution for 10¹⁴ h⁻¹ M_☉ halos at redshift z ∼ 1. We find that the form of the joint likelihood of signal pairs is generally well described by a multivariate, log-normal distribution, especially in the PH case which exhibits less halo substructure than the GO model. At fixed mass and epoch, joint deviations of signal pairs display mainly positive correlations, especially the thermal SZ effect paired with either hot gas fraction (r = 0.88/0.69 for PH/GO at z = 0) or X-ray temperature (r = 0.62/0.83). The levels of variance in X-ray luminosity, temperature, and gas mass fraction are sensitive to the physical treatment, but offsetting shifts in the latter two measures maintain a fixed 12% scatter in the integrated SZ signal under both gas treatments. We discuss halo mass selection by signal pairs, and find a minimum mass scatter of 4% in the PH model by combining thermal SZ and gas fraction measurements.

Using imaging data from the Solar TErrestrial RElations Observatory (STEREO) mission, we empirically reconstruct the time-dependent three-dimensional morphology of a coronal mass ejection (CME) from 2008 June 1, which exhibits significant variation in shape as it travels from the Sun to 1 AU, requiring us to abandon the assumption of self-similar expansion. We model the CME as a flux rope that is rather fat relative to its longitudinal extent close to the Sun, but which becomes thinner and flatter on top as the flux rope moves outward. We find best agreement with the STEREO images when the flux rope's west leg is assumed to be rotated 35° below the ecliptic plane. This orientation is consistent with previously published inferences about this CME's orientation from an analysis of in situ observations of the event from June 6 to June 7, when the CME hits STEREO-B. The agreement between these two very different kinds of analysis is encouraging. Close to 1 AU, the CME not only hits STEREO-B but also strikes a comet (Comet C/2007 W1 Boattini), which provides an additional constraint for our reconstruction efforts. Finally, we find that this CME is very instructive for assessing different methods of extracting kinematic information from measurements of elongation angles from the Sun, which is a complicated issue for measurements far from the Sun. The "fixed-ϕ" assumption that we have used successfully in the past does not work well here, and we discuss the implications for extracting reliable kinematic information from heliospheric imaging.

We have designed and built the first band-limited coronagraphic mask used for ground-based high-contrast imaging observations. The mask resides in the focal plane of the near-infrared camera PHARO at the Palomar Hale telescope and receives a well-corrected beam from an extreme adaptive optics system. Its performance on-sky with single stars is comparable to current state-of-the-art instruments: contrast levels of ∼10⁻⁵ or better at 08 in K_s after post-processing, depending on how well non-common-path errors are calibrated. However, given the mask's linear geometry, we are able to conduct additional unique science observations. Since the mask does not suffer from pointing errors down its long axis, it can suppress the light from two different stars simultaneously, such as the individual components of a spatially resolved binary star system, and search for faint tertiary companions. In this paper, we present the design of the mask, the science motivation for targeting binary stars, and our preliminary results, including the detection of a candidate M-dwarf tertiary companion orbiting the visual binary star HIP 48337, which we are continuing to monitor with astrometry to determine its association.

Solar activity and helioseismology show the limitation of the standard solar model and call for the inclusion of dynamical processes in both convective and radiative zones. In this paper, we concentrate on the radiative zone. We first recall the sensitivity of boron neutrinos to the microscopic physics included in solar standard and seismic models. We confront the neutrino predictions of the seismic model with all the detected neutrino fluxes. Then, we compute new models of the Sun including a detailed transport of angular momentum and chemicals due to internal rotation that includes meridional circulation and shear-induced turbulence. We use two stellar evolution codes: CESAM and STAREVOL to estimate the different terms. We follow three temporal evolutions of the internal rotation which differ by their initial conditions: very slow, moderate, and fast rotation, with magnetic braking at the arrival on the main sequence for the last two. We find that the meridional velocities in the present solar radiative zone are extremely small in comparison with those of the convective zone (smaller than 10⁻⁶ cm s⁻¹ instead of m s⁻¹). All models lead to a radial differential rotation profile in the radiative zone but with a significantly different contrast. We compare these profiles to the presumed solar internal rotation and show that if meridional circulation and shear turbulence were the only mechanisms transporting angular momentum within the Sun, a rather slow rotation in the young Sun is favored. We confirm the small influence of the transport by rotation on the sound speed profile but its potential impact on the chemicals in the transition region between radiation and convective zones. These models are physically more representative of the real Sun than the standard or seismic solar models but a high initial rotation, as has been considered previously, increases the disagreement with neutrinos and the sound speed in the radiative zone. This present work pushes us to pursue the inclusion of the other dynamical processes to better reproduce the observed solar profile in the whole radiative zone and to better describe the young active Sun. We also need to get a better knowledge of solar gravity mode splittings to use their constraints.

Current models and observations imply that reconnection is a key mechanism for destabilization and initiation of coronal jets. We evolve a system described by the theoretical symmetric jet formation model using two different numerical codes with the goal of studying the role of reconnection in this system. One of the codes is the Eulerian adaptive mesh code ARMS, which simulates magnetic reconnection through numerical diffusion. The quasi-Lagrangian FLUX code, on the other hand, is ideal and able to evolve the system without reconnection. The ideal nature of FLUX allows us to provide a control case of evolution without reconnection. We find that during the initial symmetric and ideal phase of evolution, both codes produce very similar morphologies and energy growth. The symmetry is then broken by a kink-like motion of the axis of rotation, after which the two systems diverge. In ARMS, current sheets formed and reconnection rapidly released the stored magnetic energy. In FLUX, the closed field remained approximately constant in height while expanding in width and did not release any magnetic energy. We find that the symmetry threshold is an ideal property of the system, but the lack of energy release implies that the observed kink is not an instability. Because of the confined nature of the FLUX system, we conclude that reconnection is indeed necessary for jet formation in symmetric jet models in a uniform coronal background field.

The presence of twisted flux ropes (TFRs) in pre-eruptive/flaring magnetic configurations is of main interest for our understanding of the structure and dynamics of the solar corona. On the one hand, their presence is a key ingredient in several theoretical models for the magnetic support of material in filaments, or triggering of coronal mass ejections as well as the emergence of structures from the convection zone into the corona. On the other hand, several observations have shown the presence of twist and shear during eruptive and flaring phases of eruptive phenomena. In this paper, we consider the determination of the magnetic structure of active region (AR) 10953 observed by Hinode and reconstructed using our two nonlinear force-free models. We show that the reconstructed magnetic configurations exhibit a TFR along the southern part of the neutral line. Moreover, the location of the magnetic dips within the TFR agrees within a good level of accuracy with the Hα images taken by SMART and the vertically integrated current density recovers the main structure present in Hinode/XRT images. The free magnetic energy is also found to be large enough to power the two C-class flares of the following days. We finally compare our results with those of Su et al. who proposed an interesting model of the same AR in which a TFR is inserted at the same location using the flux rope insertion method.

We investigate through hydrodynamic simulations the destruction of newly formed dust grains by sputtering in the reverse shocks of supernova (SN) remnants. Using an idealized setup of a planar shock impacting a dense, spherical clump, we implant a population of Lagrangian particles into the clump to represent a distribution of dust grains in size and composition. We then post-process the simulation output to calculate the grain sputtering for a variety of species and size distributions. We explore the parameter space appropriate for this problem by altering the overdensity of the ejecta clumps and the speed of the reverse shocks. Since radiative cooling could lower the temperature of the medium in which the dust is embedded and potentially protect the dust by slowing or halting grain sputtering, we study the effects of different cooling methods over the timescale of the simulations. In general, our results indicate that grains with radii less than 0.1 μm are sputtered to much smaller radii and often destroyed completely, while larger grains survive their interaction with the reverse shock. We also find that, for high ejecta densities, the percentage of dust that survives is strongly dependent on the relative velocity between the clump and the reverse shock, causing up to 50% more destruction for the highest velocity shocks. The fraction of dust destroyed varies widely across grain species, ranging from total destruction of Al₂O₃ grains to minimal destruction of Fe grains (only 20% destruction in the most extreme cases). C and SiO₂ grains show moderate to strong sputtering as well, with 38% and 80% mass loss. The survival rate of grains formed by early SNe is crucial in determining whether or not they can act as the "dust factories" needed to explain high-redshift dust.