Table of contents

A neutron capture cross section for the ¹¹²Cd(n, γ)¹¹³Cd^m reaction has been measured with neutrons provided from a nuclear reactor in order to study the astrophysical origin of a rare p-process isotope ¹¹⁵Sn, which may be produced by a nucleosynthesis flow through ¹¹³Cd^m in the s-process. We have obtained the thermal neutron capture cross section of 0.028 ± 0.009 [b] and the resonance integral of 1.1 ± 0.3 [b] using a cadmium difference method. The cross section ratio of the isomer to the ground state has been calculated as a function of the incident neutron energy, E, by using a statistical model. The calculated ratios are almost constant over a wide range of E < 100 keV. We have evaluated the s-process contribution to the solar abundance of ¹¹⁵Sn using the classical steady-flow model with various astrophysical parameters. This calculated result has shown that the production through ¹¹³Cd^m may give minor contribution to ¹¹⁵Sn.

For an optical monitoring blazar sample set whose typical minimum variability timescale is about 1 hr, we estimate a mean value of the viscosity parameter in their accretion disk. We assume that optical variability on timescales of hours is caused by local instabilities in the inner accretion disk. Comparing the observed variability timescales to the thermal timescales of α-disk models, we could obtain constraints on the viscosity parameter (α) and the intrinsic Eddington ratio ($L^{\rm in}/L_{\rm Edd}=\dot{m}$), 0.104 ⩽ α ⩽ 0.337, and 0.0201 ⩽ Lⁱⁿ/L_Edd ⩽ 0.1646. These narrow ranges suggest that all these blazars are observed in a single state, and thus provide a new evidence for the unification of flat-spectrum radio quasars and BL Lacs into a single blazar population. The values of α we derive are consistent with the theoretical expectation α ∼ 0.1–0.3 of Narayan & Mcclintock for advection-dominated accretion flow and are also compatible with Pessah et al.'s predictions (α ⩾ 0.1) by numerical simulations in which magnetohydrodynamic turbulence is driven by the saturated magnetorotational instability.

In our Galaxy there are 64 Be X-ray binaries known to date. Out of these, 42 host a neutron star (NS), and for the remainder the nature of the companion is unknown. None, so far, are known to host a black hole (BH). There seems to be no apparent mechanism that would prevent formation or detection of Be stars with BHs. This disparity is referred to as a missing Be–BH X-ray binary problem. We point out that current evolutionary scenarios that lead to the formation of Be X-ray binaries predict that the ratio of binaries with NSs to the ones with BHs is rather high, F_NStoBH ∼ 10–50, with the more likely formation models providing the values at the high end. The ratio is a natural outcome of (1) the stellar initial mass function that produces more NSs than BHs and (2) common envelope evolution (i.e., a major mechanism involved in the formation of interacting binaries) that naturally selects progenitors of Be X-ray binaries with NSs (binaries with comparable mass components have more likely survival probabilities) over ones with BHs (which are much more likely to be common envelope mergers). A comparison of this ratio (i.e., F_NStoBH ∼ 30) with the number of confirmed Be–NS X-ray binaries (42) indicates that the expected number of Be–BH X-ray binaries is of the order of only ∼0–2. This is entirely consistent with the observed Galactic sample.

We present a large X-ray-selected serendipitous cluster survey based on a novel joint analysis of archival Chandra and XMM-Newton data. The survey provides enough depth to reach clusters of flux of ≈10⁻¹⁴ergcm⁻²s⁻¹ near z≈ 1 and simultaneously a large-enough sample to find evidence for the strong evolution of clusters expected from structure formation theory. We detected a total of 723 clusters of which 462 are newly discovered clusters with greater than 6σ significance. In addition, we also detect and measure 261 previously known clusters and groups that can be used to calibrate the survey. The survey exploits a technique that combines the exquisite Chandra imaging quality with the high throughput of the XMM-Newton telescopes using overlapping survey regions. A large fraction of the contamination from active galactic nucleus point sources is mitigated by using this technique. This results in a higher sensitivity for finding clusters of galaxies with relatively few photons and a large part of our survey has a flux sensitivity between 10⁻¹⁴ and 10⁻¹⁵ergcm⁻²s⁻¹. The survey covers 41.2 deg² of overlapping Chandra and XMM-Newton fields and 122.2 deg² of non-overlapping Chandra data. We measure the log N–log S distribution and fit it with a redshift-dependent model characterized by a luminosity distribution proportional to $e^{-\frac{z}{z_0}}$. We find z₀ to be in the range 0.7–1.3, indicative of rapid cluster evolution, as expected for cosmic structure formation using parameters appropriate to the concordance cosmological model. Confirmation of our cluster detection efficiency through optical follow-up studies currently in progress will help to strengthen this conclusion and eventually allow to use these data to derive tight constraints on cosmological parameters.

We describe the infrared properties of a large sample of early-type galaxies, comparing data from the Spitzer archive with Ks-band emission from the Two Micron All Sky Survey. While most representations of this data result in correlations with large scatter, we find a remarkably tight relation among colors formed by ratios of luminosities in Spitzer-Multiband Imaging Photometer bands (24, 70, and 160 μm) and the Ks band. Remarkably, this correlation among E and S0 galaxies follows that of nearby normal galaxies of all morphological types. In particular, the tight infrared color–color correlation for S0 galaxies alone follows that of the entire Hubble sequence of normal galaxies, roughly in order of galaxy type from ellipticals to spirals to irregulars. The specific star formation rate (SFR) of S0 galaxies estimated from the 24 μm luminosity increases with decreasing K-band luminosity (or stellar mass) from essentially zero, as with most massive ellipticals, to rates typical of irregular galaxies. Moreover, the luminosities of the many infrared-luminous S0 galaxies can significantly exceed those of the most luminous (presumably post-merger) E galaxies. SFRs in the most infrared-luminous S0 galaxies approach 1–10 solar masses per year. Consistently, with this picture we find that while most early-type galaxies populate an infrared red sequence, about 24% of the objects (mostly S0s) are in an infrared blue cloud together with late-type galaxies. For those early-type galaxies also observed at radio frequencies, we find that the far-infrared luminosities correlate with the mass of neutral and molecular hydrogen, but the scatter is large. This scatter suggests that the star formation may be intermittent or that similar S0 galaxies with cold gaseous disks of nearly equal mass can have varying radial column density distributions that alter the local and global SFRs.

This paper presents a scenario for the chromospheric evaporation during solar flares, which is inspired by the chain of events leading to the formation of auroral arcs and ionospheric evacuation during magnetospheric substorms. The plasma, ejected from high coronal altitudes during a flare reconnection event, accumulates at the tops of coronal loops by braking of the reconnection flow, possibly by fast shock formation. A high-beta layer forms and distorts the magnetic field. Energy contained in magnetic shear stresses is transported as Alfvén waves from the loop-top toward the chromosphere. It is shown that under these conditions the Alfvén waves carry enough energy to feed the chromospheric evaporation process. The second subject of this investigation is identification of the most effective energy dumping or wave dissipation process. Several processes are being analyzed: ion–neutral collisions, classical and anomalous field-aligned current dissipation, and critical velocity ionization. All of them are being discarded, either because they turn out to be insufficient or imply very unlikely physical properties of the wave modes. It is finally concluded that turbulent fragmentation of the Alfvén waves entering the chromosphere can generate the required damping. The basic process would be phase mixing caused by a strongly inhomogeneous distribution of Alfvénic phase speed and laminar flow breakup by Kelvin–Helmholtz (K–H) instability. The filamentary (fibril) structure of the chromosphere thus appears to be essential for the energy conversion, in which the K–H instability is the first step in a chain of processes leading to ion thermalization, electron heating, and neutral particle ionization. Quantitative estimates suggest that a transverse structure with scales not far below 100 km suffices to produce strong wave damping within a few seconds. Nonthermal broadening of some metallic ion lines observed during the pre-impulsive rise phase of a flare might be a residue of the turbulent breakup process.

The Far InfraRed Absolute Spectrophotometer data are independently recalibrated using the Wilkinson Microwave Anisotropy Probe data to obtain a cosmic microwave background (CMB) temperature of 2.7260 ± 0.0013. Measurements of the temperature of the CMB are reviewed. The determination from the measurements from the literature is CMB temperature of 2.72548 ± 0.00057 K.

We present polarization observations of the dust continuum emission from the young star-forming region IRAS 16293. These observations of IRAS 16293, which is a binary system, were conducted by the Submillimeter Array at an observing frequency of 341.5 GHz (λ ∼  880 μm) and with high angular resolution (∼2''–3''). We find that the large-scale global direction of the field, which is perpendicular to the observed polarization, appears to be along the dust ridge where the emission peaks. On smaller scales we find that the field structure is significantly different for the two components of the binary. The first component, source A, shows a magnetic field structure that is "hourglass" shaped as predicted from theoretical models of low-mass star formation in the presence of strong magnetic fields. However, the other component, source B, shows a relatively ordered magnetic field with no evidence of any deformation. We have possibly detected a third younger outflow from source A as seen in the SiO emission, which is in addition to the two well-known powerful bipolar outflows in this kinematically active region. There is an observed decrease in polarization toward the center and this "polarization hole" is similar to decreases seen in other young star-forming regions. Our calculations show that in IRAS 16293 the magnetic energy is stronger than the turbulent energy but is approximately similar to the centrifugal energy. There is a considerable misalignment between the outflow direction and the magnetic field axis, and this is roughly in agreement with model predictions where the magnetic energy is comparable to the centrifugal energy. In conjunction with other observations of the kinematics as determined from the outflow energetics and chemical differentiation, we find that our results provide additional evidence to show that the two protostars appear to be in different stages during their evolution.

The quasar SDSS J105041.35+345631.3 (z = 0.272) has broad emission lines blueshifted by 3500 km s⁻¹ relative to the narrow lines and the host galaxy. Such an object may be a candidate for a recoiling supermassive black hole, a binary black hole, a superposition of two objects, or an unusual geometry for the broad emission-line region. The absence of narrow lines at the broad line redshift argues against superposition. New Keck spectra of J1050+3456 place tight constraints on the binary model. The combination of large velocity shift and symmetrical Hβ profile, as well as aspects of the narrow line spectrum, make J1050+3456 an interesting candidate for black hole recoil. Other aspects of the spectrum, however, suggest that the object is most likely an extreme case of a "double-peaked emitter." We discuss possible observational tests to determine the true nature of this exceptional object.

θ¹ Ori E is a young, moderate mass binary system, a rarely observed case of spectral-type G-giants of about 3 solar masses, which are still collapsing toward the main sequence, where they presumably become X-ray faint. We have obtained high-resolution X-ray spectra with Chandra and find that the system is very active and similar to coronal sources, having emission typical of magnetically confined plasma. It has a broad temperature distribution with a hot component and significant high energy continuum; narrow emission lines from H- and He-like ions, as well as a range of Fe ions, and relative luminosity, L_x/L_bol = 10⁻³, at the saturation limit. Density, while poorly constrained, is consistent with the low density limits, our upper limits being n_e < 10¹³ cm^-3 for Mg xi and n_e < 10¹² cm^-3 for Ne ix. Coronal elemental abundances are sub-solar, with Ne being the highest at about 0.4 times solar. We find a possible trend in Trapezium hot plasmas toward low relative abundances of Fe, O, and Ne, which is hard to explain in terms of the dust depletion scenarios of low-mass young stars. Variability was unusually low during our observations relative to other coronally active stars. Qualitatively, the emission is similar to post-main-sequence G-stars. Coronal structures could be compact or comparable to the dimensions of the stellar radii. From comparison to X-ray emission from similar mass stars at various evolutionary epochs, we conclude that the X-rays in θ¹ Ori E are generated by a convective dynamo, present during contraction, but which will vanish during the main-sequence epoch possibly to be resurrected during post-main-sequence evolution.

We use time-varying models of the coupled evolution of the H i, H₂ gas phases and stars in galaxy-sized numerical simulations to (1) test for the emergence of the Kennicutt–Schmidt (K–S) and the H₂–pressure relation, (2) explore a realistic H₂-regulated star formation recipe which brings forth a neglected and potentially significant SF-regulating factor, and (3) go beyond typical galactic environments (for which these galactic empirical relations are deduced) to explore the early evolution of very gas-rich galaxies. In this work, we model low-mass galaxies (M_baryon ⩽ 10⁹ M_☉), while incorporating an independent treatment of CO formation and destruction, the most important tracer molecule of H₂ in galaxies, along with that for the H₂ gas itself. We find that both the K–S and the H₂–pressure empirical relations can robustly emerge in galaxies after a dynamic equilibrium sets in between the various interstellar medium (ISM) states, the stellar component and its feedback (T ≳ 1 Gyr). The only significant dependence of these relations seems to be for the CO-derived (and thus directly observable) ones, which show a strong dependence on the ISM metallicity. The H₂-regulated star formation recipe successfully reproduces the morphological and quantitative aspects of previous numerical models while doing away with the star formation efficiency parameter. Most of the H i → H₂ mass exchange is found taking place under highly non-equilibrium conditions necessitating a time-dependent treatment even in typical ISM environments. Our dynamic models indicate that the CO molecule can be a poor, nonlinear, H₂ gas tracer. Finally, for early evolutionary stages (T ≲ 0.4 Gyr), we find significant and systematic deviations of the true star formation from that expected from the K–S relation, which are especially pronounced and prolonged for metal-poor systems. The largest such deviations occur for the very gas-rich galaxies, where deviations of a factor ∼3–4 in global star formation rate (SFR) can take place with respect to those expected from the CO-derived K–S relation. This is particularly important since gas-rich systems at high redshifts could appear as having unusually high SFRs with respect to their CO-bright H₂ gas reservoirs. This points to a possibly serious deficiency of K–S relations as elements of the sub-grid physics of star formation in simulations of structure formation in the early universe.

We present the first results from the SWARMS survey, an ongoing project to identify compact white dwarf (WD) binaries in the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS). The first object identified by SWARMS, SDSS 1257+5428, is a single-lined spectroscopic binary in a circular orbit with a period of 4.56 hr and a semiamplitude of 322.7 ± 6.3 km s^-1. From the spectrum and photometry, we estimate a WD mass of 0.92^+0.28_−0.32M_☉. Together with the orbital parameters of the binary, this implies that the unseen companion must be more massive than 1.62^+0.20_−0.25M_☉, and is in all likelihood either a neutron star or a black hole. At an estimated distance of 48⁺¹⁰₋₁₉ pc, this would be the closest known stellar remnant of a supernova explosion.

We propose the existence of ultracompact minihalos as a new type of massive compact halo object (MACHO) and suggest an observational test to discover them. These new MACHOs are a powerful probe into the nature of dark matter and physics in the high-energy universe. Non-Gaussian energy-density fluctuations produced at phase transitions (e.g., QCD) or by features in the inflation potential can trigger primordial black hole (PBH) formation if their amplitudes are δ ≳ 30%. We show that a PBH accumulates over time a sufficiently massive and compact minihalo to be able to modify or dominate its microlensing magnification light curve. Perturbations of amplitude 0.03% ≲ δ ≲ 30% are too small to form PBHs, but can nonetheless seed the growth of ultracompact minihalos. Thus, the likelihood of ultracompact minihalos as MACHOs is greater than that of PBHs. In addition, depending on their mass, they may be sites of formation of the first Population III stars. Ultracompact minihalos and PBHs produce a microlensing light curve that can be distinguished from that of a "point-like" object if high-quality photometric data are taken for a sufficiently long time after the peak of the magnification event. This enables them to be detected below the stellar-lensing "background" toward both the Magellanic Clouds and the Galactic bulge.

We report observations of 15 high-redshift (z = 1 − 5) galaxies at 350 μm using the Caltech Submillimeter Observatory and Submillimeter High Angular Resolution Camera II array detector. Emission was detected from eight galaxies, for which far-infrared luminosities, star formation rates (SFRs), total dust masses, and minimum source size estimates are derived. These galaxies have SFRs and star formation efficiencies comparable to other high-redshift molecular emission line galaxies. The results are used to test the idea that star formation in these galaxies occurs in a large number of basic units, the units being similar to star-forming clumps in the Milky Way. The luminosity of these extreme galaxies can be reproduced in a simple model with (0.9–30)×10⁶ dense clumps, each with a luminosity of 5 × 10⁵L_☉, the mean value for such clumps in the Milky Way. Radiative transfer models of such clumps can provide reasonable matches to the overall spectral energy distributions (SEDs) of the galaxies. They indicate that the individual clumps are quite opaque in the far-infrared. Luminosity-to-mass ratios vary over two orders of magnitude, correlating strongly with the dust temperature derived from simple fits to the SED. The gas masses derived from the dust modeling are in remarkable agreement with those from CO luminosities, suggesting that the assumptions going into both calculations are reasonable.

Tidal friction in exoplanet systems, driven by orbits that allow for durable nonzero eccentricities at short heliocentric periods, can generate internal heating far in excess of the conditions observed in our own solar system. Secular perturbations or a notional 2:1 resonance between a hot Earth and hot Jupiter can be used as a baseline to consider the thermal evolution of convecting bodies subject to strong viscoelastic tidal heating. We compare results first from simple models using a fixed Quality factor and Love number, and then for three different viscoelastic rheologies: the Maxwell body, the Standard Anelastic Solid (SAS), and the Burgers body. The SAS and Burgers models are shown to alter the potential for extreme tidal heating by introducing the possibility of new equilibria and multiple response peaks. We find that tidal heating tends to exceed radionuclide heating at periods below 10–30 days, and exceed insolation only below 1–2 days. Extreme cases produce enough tidal heat to initiate global-scale partial melting, and an analysis of tidal limiting mechanisms such as advective cooling for earthlike planets is discussed. To explore long-term behaviors, we map equilibria points between convective heat loss and tidal heat input as functions of eccentricity. For the periods and magnitudes discussed, we show that tidal heating, if significant, is generally detrimental to the width of habitable zones.

The high-mass X-ray binary 4U 1901+03 is reported to have a pulse profile evolving with the X-ray luminosity and energy during its outburst in 2003 February–July: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by the Rossi X-ray Timing Explorer. We find that the spectra are phase dependent. At the beginning of the outburst, the maximum of the optical depth for Compton scattering is near the major phase peak. During the decay of the outburst, the optical depth has the maximum away from the main peak of the pulse profile. For each observation, Fe Kα emission line is detected in the phase-resolved spectra, and its flux is constant across the pulse phases. This suggests that the origin of the Fe emission is from the accretion disk, not the surface of the neutron star.

We investigate the properties of "star-forming regions" in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. We study the properties (density, total gas + stars mass, stellar mass, velocity dispersion, and star formation rate (SFR)) of the cloud hosting the first local, isolated "star formation" event and compare them with those of the cloud formed by the central, global collapse event. In this simulation, the velocity dispersions at all scales are caused primarily by infall motions rather than by random turbulence. We suggest that the small-scale isolated collapses may be representative of low- to intermediate-mass star-forming regions, with gas masses (M_gas) of hundreds of solar masses, velocity dispersions σ_v ∼ 0.7 km s⁻¹, and SFRs ∼3 × 10⁻⁵M_☉ yr⁻¹, while the large-scale, massive ones may be representative of massive star-forming regions, with M_gas of thousands of solar masses, σ_v∼ a few km s⁻¹, and SFRs ∼3 × 10⁻⁴M_☉ yr⁻¹. We also compare the statistical distributions of the physical properties of the dense cores appearing in the central region of massive collapse with those from a recent survey of the massive star-forming region in the Cygnus X molecular cloud, finding that the observed and simulated distributions are in general very similar. However, we find that the star formation efficiency per free-fall time (SFE_ff) of the high mass region, similar to that of OMC-1, is low, ∼0.04. In the simulated cloud, this is not a consequence of a "slow" SFR in a nearly hydrostatic cloud supported by turbulence, but rather of the region accreting mass at a high rate. Thus, we find that measuring a low SFE_ff may be incorrectly interpreted as implying a lifetime much longer than the core's local free-fall time, and an SFR much slower than that given by the free-fall rate, if the accretion is not accounted for. We suggest that rather than requiring a low value of the SFE_ff everywhere in the Galaxy, attaining a globally low specific SFR requires star formation to be a spatially intermittent process, so that most of the mass in a giant molecular cloud (GMC) is not participating in the SF process at any given time. Locally, the specific SFR of a star-forming region can be much larger than the global GMC's average.

We present Chandra ACIS-I and ACIS-S observations (∼200 ks in total) of the X-ray luminous elliptical galaxy NGC 4636, located in the outskirts of the Virgo cluster. A soft band (0.5–2 keV) image shows the presence of a bright core in the center surrounded by an extended X-ray corona and two pronounced quasi-symmetric, 8 kpc long, arm-like features. Each of these features defines the rim of an ellipsoidal bubble. An additional bubble-like feature, whose northern rim is located ∼2 kpc south of the northeastern arm, is detected as well. We present surface brightness and temperature profiles across the rims of the bubbles, showing that their edges are sharp and characterized by temperature jumps of about 20%–25%. Through a comparison of the observed profiles with theoretical shock models, we demonstrate that a scenario where the bubbles were produced by shocks, probably driven by energy deposited off-center by jets, is the most viable explanation to the X-ray morphology observed in the central part of NGC 4636. As a confirmation to this scenario, radio jets extending toward the bubbles and a central weak X-ray and radio source are detected and are most likely the signs of active galactic nuclei activity which was more intense in the past. A bright dense core of ∼1 kpc radius is observed at the center of NGC 4636. A sharp decline in surface brightness from the core to the ambient gas is observed and is not accompanied by a variation in the temperature and thus could not be in thermal pressure equilibrium. However, the bright core could be a long-lived feature if the radio jets are acting as a balancing factor to thermal pressure or if the bright core is produced by steep abundance gradients.

Nonlinear force-free fields are the most general case of force-free fields, but the hardest to model as well. There are numerous methods of computing such fields by extrapolating vector magnetograms from the photosphere, but very few attempts have so far made quantitative use of coronal morphology. We present a method to make such quantitative use of X-ray and EUV images of coronal loops. Each individual loop is fit to a field line of a linear force-free field, allowing the estimation of the field line's twist, three-dimensional geometry, and the field strength along it. We assess the validity of such a reconstruction since the actual corona is probably not a linear force-free field, and that the superposition of linear force-free fields is generally not itself a force-free field. To do so, we perform a series of tests on nonlinear force-free fields, described in Low & Lou. For model loops we project field lines onto the photosphere. We compare several results of the method with the original field, in particular the three-dimensional loop shapes, local twist (coronal α), distribution of twist in the model photosphere, and strength of the magnetic field. We find that (1) for these trial fields, the method reconstructs twist with a mean absolute deviation of at most 15% of the range of photospheric twist, (2) heights of the loops are reconstructed with a mean absolute deviation of at most 5% of the range of trial heights, and (3) the magnitude of non-potential contribution to a photospheric field is reconstructed with a mean absolute deviation of at most 10% of the maximal value.

Modern supernova (SN) surveys are now uncovering stellar explosions at rates that far surpass what the world's spectroscopic resources can handle. In order to make full use of these SN data sets, it is necessary to use analysis methods that depend only on the survey photometry. This paper presents two methods for utilizing a set of SN light-curve templates to classify SN objects. In the first case, we present an updated version of the Bayesian Adaptive Template Matching program (BATM). To address some shortcomings of that strictly Bayesian approach, we introduce a method for Supernova Ontology with Fuzzy Templates (SOFT), which utilizes fuzzy set theory for the definition and combination of SN light-curve models. For well-sampled light curves with a modest signal-to-noise ratio (S/N >10), the SOFT method can correctly separate thermonuclear (Type Ia) SNe from core collapse SNe with ⩾98% accuracy. In addition, the SOFT method has the potential to classify SNe into sub-types, providing photometric identification of very rare or peculiar explosions. The accuracy and precision of the SOFT method are verified using Monte Carlo simulations as well as real SN light curves from the Sloan Digital Sky Survey and the SuperNova Legacy Survey. In a subsequent paper, the SOFT method is extended to address the problem of parameter estimation, providing estimates of redshift, distance, and host galaxy extinction without any spectroscopy.

We present a large sample (20 in total) of optical spectra of Small Magellanic Cloud (SMC) High-Mass X-ray Binaries obtained with the 2dF spectrograph at the Anglo–Australian Telescope. All of these sources are found to be Be/X-ray binaries (Be–XRBs), while for five sources we present original classifications. Several statistical tests on this expanded sample support previous findings for similar spectral-type distributions of Be–XRBs and Be field stars in the SMC, and of Be–XRBs in the Large Magellanic Cloud and the Milky Way, although this could be the result of small samples. On the other hand, we find that Be–XRBs follow a different distribution than Be stars in the Galaxy, also in agreement with previous studies. In addition, we find similar Be spectral-type distributions between the Magellanic Clouds samples. These results reinforce the relation between the orbital period and the equivalent width of the Hα line that holds for Be–XRBs. SMC Be stars have larger Hα equivalent widths when compared to Be–XRBs, supporting the notion of circumstellar disk truncation by the compact object.

We present Hubble Space Telescope optical coronagraphic polarization imaging observations of the dusty debris disk HD 61005. The scattered light intensity image and polarization structure reveal a highly inclined disk with a clear asymmetric, swept back component, suggestive of significant interaction with the ambient interstellar medium (ISM). The combination of our new data with the published 1.1 μm discovery image shows that the grains are blue scattering with no strong color gradient as a function of radius, implying predominantly submicron-sized grains. We investigate possible explanations that could account for the observed swept back, asymmetric morphology. Previous work has suggested that HD 61005 may be interacting with a cold, unusually dense interstellar cloud. However, limits on the intervening interstellar gas column density from an optical spectrum of HD 61005 in the Na i D lines render this possibility unlikely. Instead, HD 61005 may be embedded in a more typical warm, low-density cloud that introduces secular perturbations to dust grain orbits. This mechanism can significantly distort the ensemble disk structure within a typical cloud crossing time. For a counterintuitive relative flow direction—parallel to the disk midplane—we find that the structures generated by these distortions can very roughly approximate the HD 61005 morphology. Future observational studies constraining the direction of the relative ISM flow will thus provide an important constraint for future modeling. Independent of the interpretation for HD 61005, we expect that interstellar gas drag likely plays a role in producing asymmetries observed in other debris disk systems, such as HD 15115 and δ Velorum.

We report on the second Astrorivelatore Gamma a Immagini Leggero (AGILE) multiwavelength campaign of the blazar 3C 454.3 during the first half of 2007 December. This campaign involved AGILE, Spitzer, Swift, Suzaku, the Whole Earth Blazar Telescope (WEBT) consortium, the Rapid Eye Mount (REM), and the Multicolor Imaging Telescopes for Survey and Monstrous Explosions (MITSuME) telescopes, offering a broadband coverage that allowed for a simultaneous sampling of the synchrotron and inverse Compton (IC) emissions. The two-week AGILE monitoring was accompanied by radio to optical monitoring by WEBT and REM, and by sparse observations in mid-infrared and soft/hard X-ray energy bands performed by means of Target of Opportunity observations by Spitzer, Swift, and Suzaku, respectively. The source was detected with an average flux of ∼250 × 10⁻⁸ photons cm⁻² s⁻¹ above 100 MeV, typical of its flaring states. The simultaneous optical and γ-ray monitoring allowed us to study the time lag associated with the variability in the two energy bands, resulting in a possible ≲one-day delay of the γ-ray emission with respect to the optical one. From the simultaneous optical and γ-ray fast flare detected on December 12, we can constrain the delay between the γ-ray and optical emissions within 12 hr. Moreover, we obtain three spectral energy distributions (SEDs) with simultaneous data for 2007 December 5, 13, and 15, characterized by the widest multifrequency coverage. We found that a model with an external Compton on seed photons by a standard disk and reprocessed by the broad-line regions does not describe in a satisfactory way the SEDs of 2007 December 5, 13, and 15. An additional contribution, possibly from the hot corona with T = 10⁶ K surrounding the jet, is required to account simultaneously for the softness of the synchrotron and the hardness of the IC emissions during those epochs.

We report the behaviors of the spines in a quiescent prominence from the observations on 2008 January 15 made with Hinode/SOT in Hα +0.076 Å, Hα−0.34 Å, and Ca ii H line filters. Two spines (1 and 2) are visible in this event. In the spacetime plots of the Hα and Ca ii intensities, the two spines seem to gradually move closer together, and finally merge, then separate again. Their behaviors are separated into two kinds of typical motions. On the Doppler diagrams, the spine 1 has a dominant redshift, and spine 2 favors a blueshift, which reveals that the spines 1 and 2 firstly display the drifting motions in opposite directions. The former is drifting northward, while the latter drifts southward. Second, both spines display large-scale oscillating motions. Their oscillating velocities, amplitudes, and periods have average values of 3 km s⁻¹, ±5 Mm, and 98 minutes, respectively, indicating a small-amplitude oscillation with a long period. After the sinusoidal fitting, both spines almost exhibit an antiphase oscillating motions. The spine 2 oscillates 135° ahead of the spine 1. Such antiphase oscillations would reflect the coupling of the transverse oscillations of the spines in this prominence.

The minimal cooling paradigm for neutron star cooling assumes that enhanced cooling due to neutrino emission from any direct Urca process, due either to nucleons or to exotica such as hyperons, Bose condensates, or deconfined quarks, does not occur. Previous studies showed that the observed temperatures of young, cooling, isolated neutron stars with ages between 10² and 10⁵ yr, with the possible exception of the pulsar in the supernova remnant CTA 1, are consistent with predictions of the minimal cooling paradigm as long as the neutron ³P₂ pairing gap present in the stellar core is of moderate size. Recently, it has been found that Cooper-pair neutrino emission from the vector channel is suppressed by a large factor, of the order of 10⁻³, compared to the original estimates that violated vector current conservation. We show that Cooper-pair neutrino emission remains, nevertheless, an efficient cooling mechanism through the axial channel. As a result, the elimination of neutrino emission from Cooper-paired nucleons through the vector channel has only minor effects on the long-term cooling of neutron stars within the minimal cooling paradigm. We further quantify precisely the effect of the size of the neutron ³P₂ gap and demonstrate that consistency between observations and the minimal cooling paradigm requires that the critical temperature T_c for this gap covers a range of values between T^min_c ≲ 0.2 × 10⁹ up to T^max_c ≳ 0.5 × 10⁹ in the core of the star. This range of values guarantees that the Cooper-pair neutrino emission is operating efficiently in stars with ages between 10³ to 10⁵ yr, leading to the coldest predicted temperatures for young neutron stars. In addition, it is required that young neutron stars have heterogeneous envelope compositions: some must have light-element compositions and others must have heavy-element compositions. Unless these two conditions are fulfilled, about half of the observed young cooling neutron stars are inconsistent with the minimal cooling paradigm and provide evidence for the existence of enhanced cooling.

We have studied the effects of electron–ion non-equipartition in the outer regions of relaxed clusters for a wide range of masses in the ΛCDM cosmology using one-dimensional hydrodynamic simulations. The effects of the non-adiabatic electron heating efficiency, β, on the degree of non-equipartition are also studied. Using the gas fraction f_gas = 0.17 (which is the upper limit for a cluster), we give a conservative lower limit of the non-equipartition effect on clusters. We have shown that for a cluster with a mass of M_vir ∼ 1.2 × 10¹⁵ M_☉, electron and ion temperatures differ by less than a percent within the virial radius R_vir. The difference is ≈20% for a non-adiabatic electron heating efficiency of β ∼ 1/1800 to 0.5 at ∼1.4R_vir. Beyond that radius, the non-equipartition effect depends rather strongly on β, and such a strong dependence at the shock radius can be used to distinguish shock heating models or constrain the shock heating efficiency of electrons. With our simulations, we have also studied systematically the signatures of non-equipartition on X-ray and Sunyaev–Zel'dovich (SZ) observables. We have calculated the effect of non-equipartition on the projected temperature and X-ray surface brightness profiles using the MEKAL emission model. We found that the effect on the projected temperature profiles is larger than that on the deprojected (or physical) temperature profiles. The non-equipartition effect can introduce a ∼10% bias in the projected temperature at R_vir for a wide range of β. We also found that the effect of non-equipartition on the projected temperature profiles can be enhanced by increasing metallicity. In the low-energy band ≲1 keV, the non-equipartition model surface brightness can be higher than that of the equipartition model in the cluster outer regions. Future X-ray observations extending to ∼R_vir or even close to the shock radius should be able to detect these non-equipartition signatures. For a given cluster, the difference between the SZ temperature decrements for the equipartition and the non-equipartition models, δΔT_SZE, is larger at a higher redshift. For the most massive clusters at z ≈ 2, the differences can be δΔT_SZE ≈ 4–5 μK near the shock radius. We also found that for our model in the ΛCDM universe, the integrated SZ bias, Y_non-eq/Y_eq, evolves slightly (at a percentage level) with redshift, which is in contrast to the self-similar model in the Einstein–de Sitter universe. This may introduce biases in cosmological studies using the f_gas technique. We discussed briefly whether the equipartition and non-equipartition models near the shock region can be distinguished by future radio observations with, for example, the Atacama Large Millimeter Array.

Following the novel development and adaptation of the Metric Space Technique (MST), a multi-scale morphological analysis of the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) was performed. The technique was adapted to perform a space-scale morphological analysis by filtering the galaxy point distributions with a smoothing Gaussian function, thus giving quantitative structural information on all size scales between 5 and 250 Mpc. The analysis was performed on a dozen slices of a volume of space containing many newly measured galaxies from the SDSS DR5 survey. Using the MST, observational data were compared to galaxy samples taken from N-body simulations with current best estimates of cosmological parameters and from random catalogs. By using the maximal ranking method among MST output functions, we also develop a way to quantify the overall similarity of the observed samples with the simulated samples.

Radio, infrared, and optical observations of the 2006 eruption of the symbiotic recurrent nova RS Ophiuchi showed that the explosion produced non-spherical ejecta. Some of this ejected material was in the form of bipolar jets to the east and west of the central source. Here we describe X-ray observations taken with the ChandraX-ray Observatory one and a half years after the beginning of the outburst that reveal narrow, extended structure with a position angle of approximately 300° (east of north). Although the orientation of the extended feature in the X-ray image is consistent with the readout direction of the CCD detector, extensive testing suggests that the feature is not an artifact. Assuming it is not an instrumental effect, the extended X-ray structure shows hot plasma stretching more than 1900 AU from the central binary (taking a distance of 1.6 kpc). The X-ray emission is elongated in the northwest direction—in line with the extended infrared emission and some minor features in the published radio image. It is less consistent with the orientation of the radio jets and the main bipolar optical structure. Most of the photons in the extended X-ray structure have energies of less than 0.8 keV. If the extended X-ray feature was produced when the nova explosion occurred, then its 12 length as of 2007 August implies that it expanded at an average rate of more than 2 mas day⁻¹, which corresponds to a flow speed of greater than 6000 km s⁻¹ (days/1.6 kpc) in the plane of the sky. This expansion rate is similar to the earliest measured expansion rates for the radio jets.

Using a suite of progenitor models, neutrino luminosities, and two-dimensional simulations, we investigate the matter gravitational wave (GW) emission from postbounce phases of neutrino-driven core-collapse supernovae. These phases include prompt and steady-state convection, the standing accretion shock instability (SASI), and asymmetric explosions. For the stages before explosion, we propose a model for the source of GW emission. Downdrafts of the postshock-convection/SASI region strike the protoneutron star "surface" with large speeds and are decelerated by buoyancy forces. We find that the GW amplitude is set by the magnitude of deceleration and, by extension, the downdraft's speed and the vigor of postshock-convective/SASI motions. However, the characteristic frequencies, which evolve from ∼100 Hz after bounce to ∼300–400 Hz, are practically independent of these speeds (and turnover timescales). Instead, they are set by the deceleration timescale, which is in turn set by the buoyancy frequency at the lower boundary of postshock convection. Consequently, the characteristic GW frequencies are dependent upon a combination of core structure attributes, specifically the dense-matter equation of state (EOS) and details that determine the gradients at the boundary, including the accretion-rate history, the EOS at subnuclear densities, and neutrino transport. During explosion, the high frequency signal wanes and is replaced by a strong low frequency, ∼10s of Hz, signal that reveals the general morphology of the explosion (i.e., prolate, oblate, or spherical). However, current and near-future GW detectors are sensitive to GW power at frequencies ≳50 Hz. Therefore, the signature of explosion will be the abrupt reduction of detectable GW emission.

In this work, we study joint observations of Hinode/EUV Imaging Spectrometer (EIS) and Solar and Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation of Fe ix lines emitted by the same level of the high energy configuration 3s²3p⁵4p. The intensity ratios of these lines are dependent on atomic physics parameters only and not on the physical parameters of the emitting plasma, so that they are excellent tools to verify the relative intensity calibration of high-resolution spectrometers that work in the 170–200 Å and 700–850 Å wavelength ranges. We carry out extensive atomic physics calculations to improve the accuracy of the predicted intensity ratio, and compare the results with simultaneous EIS–SUMER observations of an off-disk quiet Sun region. We were able to identify two ultraviolet lines in the SUMER spectrum that are emitted by the same level that emits one bright line in the EIS wavelength range. Comparison between predicted and measured intensity ratios, wavelengths and energy separation of Fe ix levels confirms the identifications we make. Blending and calibration uncertainties are discussed. The results of this work are important for cross-calibrating EIS and SUMER, as well as future instrumentation.

We present a sensitive 870 μm survey of the Extended Chandra Deep Field South (ECDFS) combining 310 hr of observing time with the Large Apex BOlometer Camera (LABOCA) on the APEX telescope. The LABOCA ECDFS Submillimetre Survey (LESS) covers the full 30' × 30' field size of the ECDFS and has a uniform noise level of σ_{870 μm} ≈ 1.2 mJy beam⁻¹. LESS is thus the largest contiguous deep submillimeter survey undertaken to date. The noise properties of our map show clear evidence that we are beginning to be affected by confusion noise. We present a catalog of 126 submillimeter galaxies (SMGs) detected with a significance level above 3.7σ, at which level we expect five false detections given our map area of 1260 arcmin². The ECDFS exhibits a deficit of bright SMGs relative to previously studied blank fields but not of normal star-forming galaxies that dominate the extragalactic background light (EBL). This is in line with the underdensities observed for optically defined high redshift source populations in the ECDFS (BzKs, DRGs, optically bright active galactic nucleus, and massive K-band-selected galaxies). The differential source counts in the full field are well described by a power law with a slope of α = −3.2, comparable to the results from other fields. We show that the shape of the source counts is not uniform across the field. Instead, it steepens in regions with low SMG density. Towards the highest overdensities we measure a source-count shape consistent with previous surveys. The integrated 870 μm flux densities of our source-count models down to S_{870 μm} = 0.5 mJy account for >65% of the estimated EBL from COBE measurements. We have investigated the clustering of SMGs in the ECDFS by means of a two-point correlation function and find evidence for strong clustering on angular scales <1' with a significance of 3.4σ. Assuming a power-law dependence for the correlation function and a typical redshift distribution for the SMGs we derive a characteristic angular clustering scale of θ₀ = 14'' ± 7'' and a spatial correlation length of r₀ = 13 ± 6 h⁻¹ Mpc.

We present a detailed analysis of the relation between infrared luminosity and molecular line luminosity, for a variety of molecular transitions, using a sample of 34 nearby galaxies spanning a broad range of infrared luminosities (10¹⁰L_☉ < L_IR < 10^12.5L_☉). We show that the power-law index of the relation is sensitive to the critical density of the molecular gas tracer used, and that the dominant driver in observed molecular line ratios in galaxies is the gas density. As most nearby ultraluminous infrared galaxies (ULIRGs) exhibit strong signatures of active galactic nuclei (AGNs) in their center, we revisit previous claims questioning the reliability of HCN as a probe of the dense gas responsible for star formation in the presence of AGNs. We find that the enhanced HCN(1–0)/CO(1–0) luminosity ratio observed in ULIRGs can be successfully reproduced using numerical models with fixed chemical abundances and without AGN-induced chemistry effects. We extend this analysis to a total of 10 molecular line ratios by combining the following transitions: CO(1–0), HCO⁺(1–0), HCO⁺(3–2), HCN(1–0), and HCN(3–2). Our results suggest that AGNs reside in systems with higher dense gas fraction, and that chemistry or other effects associated with their hard radiation field may not dominate (NGC 1068 is one exception). Galaxy merger could be the underlying cause of increased dense gas fraction, and the evolutionary stage of such mergers may be another determinant of the HCN/CO luminosity ratio.

The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations driven by magneto-rotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model shows turbulent accretion characterized by a Shakura–Sunyaev viscosity parameter of α ∼ 10⁻², with rms density perturbations of ∼10%. We measure the statistical evolution of particle orbital properties in our simulations including mean radius, eccentricity, and velocity dispersion. We confirm random walk growth in time of all three properties, the first time that this has been done with direct orbital integration in a local model. We find that the growth rate increases with the box size used at least up to boxes of eight scale heights in horizontal size. However, even our largest boxes show velocity dispersions sufficiently low that collisional destruction of planetesimals should be unimportant in the inner disk throughout its lifetime. Our direct integrations agree with earlier torque measurements showing that type I migration dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magneto-rotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

Porosity evolution of dust aggregates is crucial in understanding dust evolution in protoplanetary disks. In this study, we present useful tools to study the coagulation and porosity evolution of dust aggregates. First, we present a new numerical method for simulating dust coagulation and porosity evolution as an extension of the conventional Smoluchowski equation. This method follows the evolution of the mean porosity for each aggregate mass simultaneously with the evolution of the mass distribution function. This method reproduces the results of previous Monte Carlo simulations with much less computational expense. Second, we propose a new collision model for porous dust aggregates on the basis of our N-body experiments on aggregate collisions. As the first step, we focus on "hit-and-stick" collisions, which involve neither compression nor fragmentation of aggregates. We first obtain empirical data on porosity changes between the classical limits of ballistic cluster–cluster and particle–cluster aggregation. Using the data, we construct a recipe for the porosity change due to general hit-and-stick collisions as well as formulae for the aerodynamical and collisional cross sections. Our collision model is thus more realistic than a previous model of Ormel et al. based on the classical aggregation limits only. Simple coagulation simulations using the extended Smoluchowski method show that our collision model explains the fractal dimensions of porous aggregates observed in a full N-body simulation and a laboratory experiment. By contrast, similar simulations using the collision model of Ormel et al. result in much less porous aggregates, meaning that this model underestimates the porosity increase upon unequal-sized collisions. Besides, we discover that aggregates at the high-mass end of the distribution can have a considerably small aerodynamical cross section per unit mass compared with aggregates of lower masses. This occurs when aggregates drift under uniform acceleration (e.g., gravity) and their collision is induced by the difference in their terminal velocities. We point out an important implication of this discovery for dust growth in protoplanetary disks.

We estimate the detection efficiency of binary gravitational lensing events through the channel of high-magnification events. From this estimation, we find that binaries in the separation ranges of 0.1 ≲ s ≲ 10, 0.2 ≲ s ≲ 5, and 0.3 ≲ s ≲ 3 can be detected with ∼100% efficiency for events with magnifications higher than A = 100, 50, and 10, respectively, where s represents the projected separation between the lens components normalized by the Einstein radius. We also find that the range of high efficiency covers nearly the whole mass-ratio range of stellar companions. Due to the high efficiency in wide ranges of parameter space, we point out that the majority of binary-lens events will be detected through the high-magnification channel in lensing surveys that focus on high-magnification events for efficient detections of microlensing planets. In addition to the high efficiency, the simplicity of the efficiency estimation makes the sample of these binaries useful in the statistical studies of the distributions of binary companions as functions of mass ratio and separation. We also discuss other implications of these events.

We present spectroscopic observations of a sample of 15 embedded young stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS spectral range: the bending mode of CO₂ ice at 15.2 μm and the ice band between 5 and 7 μm that includes contributions from the bending mode of water ice at 6 μm among other ice species. The 5–7 μm band is difficult to identify in our LMC sample due to the conspicuous presence of polycyclic aromatic hydrocarbon emission superimposed onto the ice spectra. We identify water ice in the spectra of two sources; the spectrum of one of those sources also exhibits the 6.8 μm ice feature attributed in the literature to ammonium and methanol. We model the CO₂ band in detail, using the combination of laboratory ice profiles available in the literature. We find that a significant fraction (≳50%) of CO₂ ice is locked in a water-rich component, consistent with what is observed for Galactic sources. The majority of the sources in the LMC also require a pure-CO₂ contribution to the ice profile, evidence of thermal processing. There is a suggestion that CO₂ production might be enhanced in the LMC, but the size of the available sample precludes firmer conclusions. We place our results in the context of the star formation environment in the LMC.

We present a simultaneous periodic and aperiodic timing study of the accreting millisecond X-ray pulsar SAX J1808.4-3658. We analyze five outbursts of the source and for the first time provide a full and systematic investigation of the enigmatic phenomenon of the 1 Hz flares observed during the final stages of some of the outbursts. We show that links between pulsations and 1 Hz flares might exist, and suggest that they are related with hydrodynamic disk instabilities that are triggered close to the disk–magnetosphere boundary layer when the system is entering the propeller regime.

We report on observations of TeV-selected active galactic nuclei (AGNs) made during the first 5.5 months of observations with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope (Fermi). In total, 96 AGNs were selected for study, each being either (1) a source detected at TeV energies (28 sources) or (2) an object that has been studied with TeV instruments and for which an upper limit has been reported (68 objects). The Fermi observations show clear detections of 38 of these TeV-selected objects, of which 21 are joint GeV–TeV sources, and 29 were not in the third EGRET catalog. For each of the 38 Fermi-detected sources, spectra and light curves are presented. Most can be described with a power law of spectral index harder than 2.0, with a spectral break generally required to accommodate the TeV measurements. Based on an extrapolation of the Fermi spectrum, we identify sources, not previously detected at TeV energies, which are promising targets for TeV instruments. Evidence for systematic evolution of the γ-ray spectrum with redshift is presented and discussed in the context of interaction with the extragalactic background light.

We investigate the relationship between the linewidths of broad Mg ii λ2800 and Hβ in active galactic nuclei (AGNs) to refine them as tools to estimate black hole (BH) masses. We perform a detailed spectral analysis of a large sample of AGNs at intermediate redshifts selected from the Sloan Digital Sky Survey, along with a smaller sample of archival ultraviolet spectra for nearby sources monitored with reverberation mapping (RM). Careful attention is devoted to accurate spectral decomposition, especially in the treatment of narrow-line blending and Fe ii contamination. We show that, contrary to popular belief, the velocity width of Mg ii tends to be smaller than that of Hβ, suggesting that the two species are not cospatial in the broad-line region. Using these findings and recently updated BH mass measurements from RM, we present a new calibration of the empirical prescriptions for estimating virial BH masses for AGNs using the broad Mg ii and Hβ lines. We show that the BH masses derived from our new formalisms show subtle but important differences compared to some of the mass estimators currently used in the literature.

We present deep Hubble Space Telescope NICMOS 2 F160W band observations of the central 56'' × 57'' (14 pc × 14.25 pc) region around R136 in the starburst cluster 30 Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to derive the stellar initial mass function (IMF) down to ∼1 M_☉ in order to test whether the IMF in a massive metal-poor cluster is similar to that observed in nearby young clusters and the field in our Galaxy. We estimate the mean age of the cluster to be 3 Myr by combining our F160W photometry with previously obtained HST WFPC2 optical F555W and F814W band photometry and comparing the stellar locus in the color–magnitude diagram with main sequence and pre-main sequence isochrones. The color–magnitude diagrams show the presence of differential extinction and possibly an age spread of a few megayear. We convert the magnitudes into masses adopting both a single mean age of 3 Myr isochrone and a constant star formation history from 2 to 4 Myr. We derive the IMF after correcting for incompleteness due to crowding. The faintest stars detected have a mass of 0.5 M_☉ and the data are more than 50% complete outside a radius of 5 pc down to a mass limit of 1.1 M_☉ for 3 Myr old objects. We find an IMF of $\frac{dN}{d\log M }\propto M^{-1.20\pm 0.2}$ over the mass range 1.1–20 M_☉ only slightly shallower than a Salpeter IMF. In particular, we find no strong evidence for a flattening of the IMF down to 1.1 M_☉ at a distance of 5 pc from the center, in contrast to a flattening at 2 M_☉ at a radius of 2 pc, reported in a previous optical HST study. We examine several possible reasons for the different results including the possible presence of mass segregation and the effects of differential extinction, particularly for the pre-main sequence sources. If the IMF determined here applies to the whole cluster, the cluster would be massive enough to remain bound and evolve into a relatively low-mass globular cluster.

We present the first X-ray analysis of the diffuse hot ionized gas and the point sources in IC131, after NGC604 the second most X-ray luminous giant H ii region (GHR) in M33. The X-ray emission is detected only in the south eastern part of IC131 (named IC131-se) and is limited to an elliptical region of ∼200 pc in extent. This region appears to be confined toward the west by a hemispherical shell of warm ionized gas and only fills about half that volume. Although the corresponding X-ray spectrum has 1215 counts, it cannot conclusively be told whether the extended X-ray emission is thermal, non-thermal, or a combination of both. A thermal plasma model of kT_e = 4.3 keV or a single power law of Γ ≃ 2.1 fit the spectrum equally well. If the spectrum is purely thermal (non-thermal), the total unabsorbed X-ray luminosity in the 0.35–8 keV energy band amounts to L_X = 6.8(8.7) × 10³⁵ erg s⁻¹. Among other known H ii regions IC131-se seems to be extreme regarding the combination of its large extent of the X-ray plasma, the lack of massive O stars, its unusually high electron temperature (if thermal), and the large fraction of L_X emitted above 2 keV (∼40%–53%). A thermal plasma of ∼4 keV poses serious challenges to theoretical models, as it is not clear how high electron temperatures can be produced in H ii regions in view of mass-proportional and collisionless heating. If the gas is non-thermal or has non-thermal contributions, synchrotron emission would clearly dominate over inverse Compton emission. It is not clear if the same mechanisms which create non-thermal X-rays or accelerate cosmic rays in supernova remnants can be applied to much larger scales of 200 pc. In both cases the existing theoretical models for GHRs and superbubbles do not explain the hardness and extent of the X-ray emission in IC131-se. We also detect a variable source candidate in IC131. It seems that this object (CXO J013315.10+304453.0) is a high mass X-ray binary whose optical counterpart is a B2-type star with a mass of ∼9 M_☉.

The Sun's polar fields are currently ∼40% weaker than they were during the previous three sunspot minima. This weakening has been accompanied by a corresponding decrease in the interplanetary magnetic field (IMF) strength, by a ∼20% shrinkage in the polar coronal-hole areas, and by a reduction in the solar-wind mass flux over the poles. It has also been reflected in coronal streamer structure and the heliospheric current sheet, which only showed the expected flattening into the equatorial plane after sunspot numbers fell to unusually low values in mid-2008. From latitude–time plots of the photospheric field, it has long been apparent that the polar fields are formed through the transport of trailing-polarity flux from the sunspot latitudes to the poles. To address the question of why the polar fields are now so weak, we simulate the evolution of the photospheric field and radial IMF strength from 1965 to the present, employing a surface transport model that includes the effects of active region emergence, differential rotation, supergranular convection, and a poleward bulk flow. We find that the observed evolution can be reproduced if the amplitude of the surface meridional flow is varied by as little as 15% (between 14.5 and 17 m s⁻¹), with the higher average speeds being required during the long cycles 20 and 23.

We have used the zCOSMOS-bright 10k sample to identify 3244 Spitzer/MIPS 24 μm-selected galaxies with 0.06 mJy < S_{24 μm} ≲ 0.50 mJy and I_AB < 22.5, over 1.5 deg² of the COSMOS field, and studied different spectral properties, depending on redshift. At 0.2 < z < 0.3, we found that different reddening laws of common use in the literature explain the dust extinction properties of ∼80% of our infrared (IR) sources, within the error bars. For up to 16% of objects, instead, the Hα λ6563/Hβ λ4861 ratios are too high for their IR/UV attenuations, which is probably a consequence of inhomogeneous dust distributions. In only a few of our galaxies at 0.2 < z < 0.3, the IR emission could be mainly produced by dust heated by old rather than young stars. Besides, the line ratios of ∼22% of our galaxies suggest that they might be star-formation/nuclear-activity composite systems. At 0.5 < z < 0.7, we estimated galaxy metallicities for 301 galaxies: at least 12% of them are securely below the upper-branch mass–metallicity trend, which is consistent with the local relation. Finally, we performed a combined analysis of the H_δ equivalent width versus D_n(4000) diagram for 1722 faint and bright 24 μm galaxies at 0.6 < z < 1.0, spanning two decades in mid-IR luminosity. We found that, while secondary bursts of star formation are necessary to explain the position of the most luminous IR galaxies in that diagram, quiescent, exponentially declining star formation histories can well reproduce the spectral properties of ∼40% of the less luminous sources. Our results suggest a transition in the possible modes of star formation at total IR luminosities L_TIR ≈ (3 ± 2) × 10¹¹L_☉.

The Fermi Gamma-ray Space Telescope recently detected the most energetic gamma-ray burst so far, GRB 080916C, and reported its detailed temporal properties in an extremely broad spectral range: (1) the time-resolved spectra are well described by broken power-law forms over the energy range of 10 keV–10 GeV, (2) the high-energy emission (at ε>100 MeV) is delayed by ≈5 s with respect to the ε ≲ 1 MeV emission, and (3) the emission onset times shift toward later times in higher energy bands. We show that this behavior of the high-energy emission can be explained by a model in which the prompt emission consists of two components: one is the emission component peaking at ε ∼ 1 MeV due to the synchrotron-self-Compton radiation of electrons accelerated in the internal shock of the jet and the other is the component peaking at ε ∼ 100 MeV due to up-scattering of the photospheric X-ray emission of the expanding cocoon (i.e., the hot bubble produced by dissipation of the jet energy inside the progenitor star) off the same electrons in the jet. Based on this model, we derive some constraints on the radius of the progenitor star and the total energy and mass of the cocoon of this GRB, which may provide information on the structure of the progenitor star and the physical conditions of the jet propagating in the star. The up-scattered cocoon emission could be important for other Fermi GRBs as well. We discuss some predictions of this model, including a prompt bright optical emission and a soft X-ray excess.

We have used archival Hubble Space Telecope (HST) Hα images to study the immediate environments of massive and intermediate-mass young stellar object (YSO) candidates in the Large Magellanic Cloud (LMC). The sample of YSO candidates, taken from Gruendl & Chu, was selected based on Spitzer IRAC and MIPS observations of the entire LMC and complementary ground-based optical and near-infrared observations. We found HST Hα images for 99 YSO candidates in the LMC, of which 82 appear to be genuine YSOs. More than 95% of the YSOs are found to be associated with molecular clouds. YSOs are seen in three different kinds of environments in the Hα images: in dark clouds, inside or on the tip of bright-rimmed dust pillars, and in small H ii regions. Comparisons of spectral energy distributions for YSOs in these three different kinds of environments suggest that YSOs in dark clouds are the youngest, YSOs with small H ii regions are the most evolved, and YSOs in bright-rimmed dust pillars span a range of intermediate evolutionary stages. This rough evolutionary sequence is substantiated by the presence of silicate absorption features in the Spitzer Infrared Spectrograph spectra of some YSOs in dark clouds and in bright-rimmed dust pillars, but not those of YSOs in small H ii regions. We present a discussion on triggered star formation for YSOs in bright-rimmed dust pillars or in dark clouds adjacent to H ii regions. As many as 50% of the YSOs are resolved into multiple sources in high-resolution HST images. This illustrates the importance of using high-resolution images to probe the true nature and physical properties of YSOs in the LMC.

We investigate the effect of magnetic reconnection on the boundary between open and closed magnetic field in the solar corona. The magnetic topology for our numerical study consists of a global dipole that gives rise to polar coronal holes and an equatorial streamer belt, and a smaller active-region bipole embedded inside the closed-field streamer belt. The initially potential magnetic field is energized by a rotational motion at the photosphere that slowly twists the embedded-bipole flux. Due to the applied stress, the bipole field expands outward and reconnects with the surrounding closed flux, eventually tunneling through the streamer boundary and encountering the open flux of the coronal hole. The resulting interchange reconnection between closed and open field releases the magnetic twist and free energy trapped inside the bipole onto open field lines, where they freely escape into the heliosphere along with the entrained closed-field plasma. Thereafter, the bipole field relaxes and reconnects back down into the interior of the streamer belt. Our simulation shows that the detailed properties of magnetic reconnection can be crucial to the coronal magnetic topology, which implies that both potential-field source-surface and quasi-steady magnetohydrodynamic models may often be an inadequate description of the corona and solar wind. We discuss the implications of our results for understanding the dynamics of the boundary between open and closed field on the Sun and the origins of the slow wind.

Most early radiative transfer calculations of protostellar collapse have suggested an upper limit of ∼40 M_☉ for the final stellar mass before radiation pressure can exceed the star's gravitational pull and halt the accretion. Here we perform further collapse calculations, using frequency-dependent radiation transfer coupled to a frequency-dependent dust model that includes amorphous carbon particles, silicates, and ice-coated silicates. The models start from pressure-bounded, logatropic spheres of mass between 5 M_☉ and 150 M_☉ with an initial nonsingular density profile. We find that in a logatrope the infall is never reversed by the radiative forces on the dust and that stars with masses ≳100 M_☉ may form by continued accretion. Compared to previous models that start the collapse with a ρ ∝ r⁻² density configuration, our calculations result in higher accretion times and lower average accretion rates with peak values of ∼5.8 × 10⁻⁵M_☉ yr⁻¹. The radii and bolometric luminosities of the produced massive stars (≳90 M_☉) are in good agreement with the figures reported for detected stars with initial masses in excess of 100 M_☉. The spectral energy distribution from the stellar photosphere reproduces the observed fluxes for hot molecular cores with peaks of emission from mid- to near-infrared.

We use multi-wavelength, matched aperture, integrated photometry from the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the RC3 to estimate the physical properties of 166 nearby galaxies hosting 168 well-observed Type Ia supernovae (SNe Ia). The ultraviolet (UV) imaging of local SN Ia hosts from GALEX allows a direct comparison with higher-redshift hosts measured at optical wavelengths that correspond to the rest-frame UV. Our data corroborate well-known features that have been seen in other SN Ia samples. Specifically, hosts with active star formation produce brighter and slower SNe Ia on average, and hosts with luminosity-weighted ages older than 1 Gyr produce on average more faint, fast, and fewer bright, slow SNe Ia than younger hosts. New results include that in our sample, the faintest and fastest SNe Ia occur only in galaxies exceeding a stellar mass threshold of ∼10¹⁰M_☉, leading us to conclude that their progenitors must arise in populations that are older and/or more metal rich than the general SN Ia population. A low host extinction subsample hints at a residual trend in peak luminosity with host age, after correcting for light-curve shape, giving the appearance that older hosts produce less-extincted SNe Ia on average. This has implications for cosmological fitting of SNe Ia, and suggests that host age could be useful as a parameter in the fitting. Converting host mass to metallicity and computing ⁵⁶Ni mass from the supernova light curves, we find that our local sample is consistent with a model that predicts a shallow trend between stellar metallicity and the ⁵⁶Ni mass that powers the explosion, but we cannot rule out the absence of a trend. We measure a correlation between ⁵⁶Ni mass and host age in the local universe that is shallower and not as significant as that seen at higher redshifts. The details of the age–⁵⁶Ni mass correlations at low and higher redshift imply a luminosity-weighted age threshold of ∼3 Gyr for SN Ia hosts, above which they are less likely to produce SNe Ia with ⁵⁶Ni masses above ∼0.5 M_☉.

We construct a new model of Type Ia Supernovae (SNe Ia), based on the single degenerate scenario, taking account of the metallicity dependences of white dwarf (WD) wind and the mass-stripping effect on the binary companion star. Our model naturally predicts that SN Ia lifetime distribution spans a range of 0.1–20 Gyr with the double peaks at ∼0.1 and 1 Gyr. While the present SN Ia rate in elliptical galaxies can be reproduced with the old population of the red giants+WD systems, the large SN Ia rate in radio galaxies could be explained with the young population of the main-sequence+WD systems. Because of the metallicity effect, i.e., because of the lack of winds from WDs in the binary systems, the SN Ia rate in the systems with [Fe/H] ≲−1, e.g., high-z spiral galaxies, is supposed to be very small. Our SN Ia model can give better reproduction of the [(α, Mn, Zn)/Fe]–[Fe/H] relations in the solar neighborhood than other models such as the double-degenerate scenario. The metallicity effect is more strongly required in the presence of the young population of SNe Ia. We also succeed in reproducing the galactic supernova rates with their dependence on the morphological type of galaxies, and the cosmic SN Ia rate history with a peak at z ∼ 1. At z ≳ 1, the predicted SN Ia rate decreases toward higher redshifts and SNe Ia will be observed only in the systems that have evolved with a short timescale of chemical enrichment. This suggests that the evolution effect in the supernova cosmology can be small.

We present results of a series of magnetohydrodynamic (MHD) and hydrodynamic (HD) 2.5 dimensional simulations of the morphology of outflows driven by nested wide-angle winds, i.e., winds that emanate from a central star as well as from an orbiting accretion disk. While our results are broadly relevant to nested-wind systems, we have tuned the parameters of the simulations to touch on issues in both young stellar objects and planetary nebula (PN) studies. In particular, our studies connect to open issues in the early evolution of PNs. We find that nested MHD winds exhibit marked morphological differences from the single MHD wind case along both dimensions of the flow. Nested HD winds, on the other hand, give rise mainly to geometric distortions of an outflow that is topologically similar to the flow arising from a single stellar HD wind. Our MHD results are insensitive to changes in ambient temperature between ionized and un-ionized circumstellar environments. The results are sensitive to the relative mass-loss rates and the relative speeds of the stellar and disk winds. We also present synthetic emission maps of both nested MHD and HD simulations. We find that nested MHD winds show knots of emission appearing on-axis that do not appear in the HD case.

Neutrinos emitted during the collapse, bounce, and subsequent explosion provide information about supernova dynamics. The neutrino spectra are determined by weak interactions with nuclei and nucleons in the inner regions of the star, and thus the neutrino spectra are determined by the composition of matter. The composition of stellar matter at temperature ranging from T = 1–3 MeV and densities ranging from 10⁻⁵ to 0.1 times the saturation density is explored. We examine the single-nucleus approximation commonly used in describing dense matter in supernova simulations and show that while the approximation is accurate for predicting the energy and pressure at most densities, the predicted compositions are less accurate, varying by 50% or more at the largest densities. We find that as the temperature and density increase, the single nucleus approximation systematically overpredicts the mass number of nuclei that are actually present and underestimates the contribution from lighter nuclei which are present in significant amounts.

We follow Paper I with predictions of how gas leaking through the lunar surface could influence the regolith, as might be observed via optical transient lunar phenomena (TLPs) and related effects. We touch on several processes, but concentrate on low and high flow rate extremes, which are perhaps the most likely. We model explosive outgassing for the smallest gas overpressure at the regolith base that releases the regolith plug above it. This disturbance's timescale and affected area are consistent with observed TLPs; we also discuss other effects. For slow flow, escape through the regolith is prolonged by low diffusivity. Water, found recently in deep magma samples, is unique among candidate volatiles, capable of freezing between the regolith base and surface, especially near the lunar poles. For major outgassing sites, we consider the possible accumulation of water ice. Over geological time, ice accumulation can evolve downward through the regolith. Depending on gases additional to water, regolith diffusivity might be suppressed chemically, blocking seepage and forcing the ice zone to expand to larger areas, up to km² scales, again, particularly at high latitudes. We propose an empirical path forward, wherein current and forthcoming technologies provide controlled, sensitive probes of outgassing. The optical transient/outgassing connection, addressed via Earth-based remote sensing, suggests imaging and/or spectroscopy, but aspects of lunar outgassing might be more covert, as indicated above. TLPs betray some outgassing, but does outgassing necessarily produce TLPs? We also suggest more intrusive techniques from radar to in situ probes. Understanding lunar volatiles seems promising in terms of resource exploitation for human exploration of the Moon and beyond, and offers interesting scientific goals in its own right. Many of these approaches should be practiced in a pristine lunar atmosphere, before significant confusing signals likely to be produced upon humans returning to the Moon.

Aminomethanol (NH₂CH₂OH) is formed at low temperature from the purely thermal reaction of NH₃ and H₂CO in laboratory interstellar ice analogs. We report for the first time its infrared and mass spectra. We study its reaction and desorption kinetics using Fourier transform infrared spectroscopy and mass spectrometry. Its reaction rate is estimated to be k(T) = 0.05 × exp(−4.5(kJ mol^-1)/RT) and its desorption energy to be E_des = 58 ± 2 kJ mol⁻¹. NH₂CH₂OH can also contribute to the 5–8 μm region of thermally processed ices encountered in many young stellar objects. Gas phase NH₂CH₂OH may be present in hot core regions, when the frozen material is desorbed.

Using our recently improved Monte Carlo evolution code, we study the evolution of the binary fraction in globular clusters. In agreement with previous N-body simulations, we find generally that the hard binary fraction in the core tends to increase with time over a range of initial cluster central densities for initial binary fractions ≲90%. The dominant processes driving the evolution of the core binary fraction are mass segregation of binaries into the cluster core and preferential destruction of binaries there. On a global scale, these effects and the preferential tidal stripping of single stars tend to roughly balance, leading to overall cluster binary fractions that are roughly constant with time. Our findings suggest that the current hard binary fraction near the half-mass radius is a good indicator of the hard primordial binary fraction. However, the relationship between the true binary fraction and the fraction of main-sequence stars in binaries (which is typically what observers measure) is nonlinear and rather complicated. We also consider the importance of soft binaries, which not only modify the evolution of the binary fraction, but can also drastically change the evolution of the cluster as a whole. Finally, we briefly describe the recent addition of single and binary stellar evolution to our cluster evolution code.

We propose a model for diffusive shock acceleration (DSA) in which stochastic magnetic fields in the shock precursor are generated through purely fluid mechanisms of a so-called small-scale dynamo. This contrasts with previous DSA models that considered magnetic fields amplified through cosmic ray (CR) streaming instabilities, i.e., either by way of individual particles resonant scattering in the magnetic fields, or by macroscopic electric currents associated with large-scale CR streaming. Instead, in our picture, the solenoidal velocity perturbations that are required for the dynamo to work are produced through the interactions of the pressure gradient of the CR precursor and density perturbations in the inflowing fluid. Our estimates show that this mechanism provides fast growth of magnetic field and is very generic. We argue that for supernovae shocks the mechanism is capable of generating upstream magnetic fields that are sufficiently strong for accelerating CRs up to around 10¹⁶ eV. No action of any other mechanism is necessary.

The 10 μm silicate feature observed with Spitzer in active galactic nuclei (AGNs) reveals some puzzling behavior. It (1) has been detected in emission in type 2 sources, (2) shows broad, flat-topped emission peaks shifted toward long wavelengths in several type 1 sources, and (3) is not seen in deep absorption in any source observed so far. We solve all three puzzles with our clumpy dust radiative transfer formalism. Addressing (1), we present the spectral energy distribution (SED) of SST1721+6012, the first type 2 quasar observed to show a clear 10 μm silicate feature in emission. Such emission arises in models of the AGN torus easily when its clumpy nature is taken into account. We constructed a large database of clumpy torus models and performed extensive fitting of the observed SED. We find that the cloud radial distribution varies as r^−1.5 and the torus contains 2–4 clouds along radial equatorial rays, each with optical depth at visual ∼60–80. The source bolometric luminosity is ∼3 × 10¹² L_☉. Our modeling suggests that ≲35% of objects with tori sharing these characteristics and geometry would have their central engines obscured. This relatively low obscuration probability can explain the clear appearance of the 10 μm emission feature in SST1721+6012 together with its rarity among other QSO2. Investigating (2), we also fitted the SED of PG1211+143, one of the first type 1 QSOs with a 10 μm silicate feature detected in emission. Together with other similar sources, this QSO appears to display an unusually broadened feature whose peak is shifted toward longer wavelengths. Although this led to suggestions of non-standard dust chemistry in these sources, our analysis fits such SEDs with standard galactic dust; the apparent peak shifts arise from simple radiative transfer effects. Regarding (3), we find additionally that the distribution of silicate feature strengths among clumpy torus models closely resembles the observed distribution, and the feature never occurs deeply absorbed. Comparing such distributions in several AGN samples we also show that the silicate emission feature becomes stronger in the transition from Seyfert to quasar luminosities.

We report the discovery of a Type IIn supernova (SN) in the low-metallicity dwarf galaxy J1320+2155, with an oxygen abundance 12 + log O/H = 8.0 ± 0.2. This finding is based on Sloan Digital Sky Survey (SDSS; 2008 February) and 3.5 m Apache Point Observatory (2009 February) spectra taken one year apart, and on the observations that: the Hβ and Hα emission lines show broad components corresponding to gas expansion velocities of ∼1600 km s⁻¹; the Balmer decrement is exceedingly high: the Hα/Hβ flux ratio, being more than 30, implies a very dense environment (>10⁷ cm⁻³); and the Hα broad luminosity decreases slowly, by only a factor of ∼1.8 over the course of a year, typical of the slow luminosity evolution of a Type IIn SN. Several weak coronal lines of [Fe vii] and [Fe x] are also seen in the SDSS spectrum, implying ionization of the pre-shock circumstellar medium by shock-induced X-ray emission. The galaxy J1320+2155 is the first dwarf system ever to be discovered with a Type IIn SN exhibiting coronal lines in its spectrum.

The star formation rate (SFR) and black hole accretion rate (BHAR) functions are measured to be proportional to each other at z ≲ 3. This close correspondence between SF and BHA would naturally yield a BH mass–galaxy mass correlation, whereas a BH mass–bulge mass correlation is observed. To explore this apparent contradiction, we study the SF in spheroid-dominated galaxies between z = 1 and the present day. We use 903 galaxies from the COMBO-17 survey with M_* > 2 × 10¹⁰M_☉, ultraviolet and infrared-derived SFRs from Spitzer and Galaxy Evolution Explorer, and morphologies from GEMS Hubble Space Telescope/Advanced Camera for Surveys imaging. Using stacking techniques, we find that <25% of all SF occurs in spheroid-dominated galaxies (Sérsic index n > 2.5), while the BHAR that we would expect if the global scalings held is 3 times higher. This rules out the simplest picture of co-evolution, in which SF and BHA trace each other at all times. These results could be explained if SF and BHA occur in the same events, but offset in time, for example at different stages of a merger event. However, one would then expect to see the corresponding star formation activity in early-stage mergers, in conflict with observations. We conclude that the major episodes of SF and BHA occur in different events, with the bulk of SF happening in isolated disks and most BHA occurring in major mergers. The apparent global co-evolution results from the regulation of the BH growth by the potential well of the galactic spheroid, which includes a major contribution from disrupted disk stars.

For typical models of binary statistics, 50%–80% of core-collapse supernova (ccSN) progenitors are members of a stellar binary at the time of the explosion. Independent of any consequences of mass transfer, this has observational consequences that can be used to study the binary properties of massive stars. In particular, the secondary companion to the progenitor of a Type Ib/c SN is frequently (∼50%) the more optically luminous star since the high effective temperatures of the stripped progenitors make it relatively easy for a lower luminosity, cooler secondary to emit more optical light. Secondaries to the lower mass progenitors of Type II SN will frequently produce excess blue emission relative to the spectral energy distribution of the red primary. Available data constrain the models weakly. Any detected secondaries also provide an independent lower bound on the progenitor mass and, for historical SN, show that it was not a Type Ia event. Bright ccSN secondaries have an unambiguous, post-explosion observational signature—strong, blueshifted, relatively broad absorption lines created by the developing SN remnant (SNR). These can be used to locate historical SN with bright secondaries, confirm that a source is a secondary, and, potentially, measure abundances of ccSN ejecta. Luminous, hot secondaries will re-ionize the SNR on timescales of 100–1000 yr that are faster than re-ionization by the reverse shock, creating peculiar H ii regions due to the high metallicity and velocities of the ejecta.

Using hard X-ray observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), we investigate the reliability of spectral hardening during solar flares as an indicator of related solar energetic particle (SEP) events at Earth. All RHESSI data are analyzed, from 2002 February through the end of Solar Cycle 23, thereby expanding upon recent work on a smaller sample of flares. Previous investigations have found very high success when associating soft–hard–harder (SHH) spectral behavior with energetic proton events, and confirmation of this link would suggest a correlation between electron acceleration in solar flares and SEPs seen in interplanetary space. In agreement with these past findings, we find that of 37 magnetically well-connected flares (W30−W90), 12 of 18 flares with SHH behavior produced SEP events and none of 19 flares without SHH behavior produced SEPs. This demonstrates a statistically significant dependence of SHH and SEP observations, a link that is unexplained in the standard scenario of SEP acceleration at the shock front of coronal mass ejections and encourages further investigation of the mechanisms which could be responsible.

We present a new analysis of stellar mass functions in the COSMOS field to fainter limits than has been previously probed at z ⩽ 1. The increase in dynamic range reveals features in the shape of the stellar mass function that deviate from a single Schechter function. Neither the total nor the red (passive) or blue (star-forming) galaxy stellar mass functions can be well fitted with a single Schechter function once the mass completeness limit of the sample probes below ∼3 × 10⁹ M_☉. We observe a dip or plateau at masses ∼10¹⁰ M_☉, just below the traditional M*, and an upturn toward a steep faint-end slope of α ∼ −1.7 at lower mass at all redshifts ⩽1. This bimodal nature of the mass function is not solely a result of the blue/red dichotomy. Indeed, the blue mass function is by itself bimodal at z ∼ 1. This suggests a new dichotomy in galaxy formation that predates the appearance of the red sequence. We propose two interpretations for this bimodal distribution. If the gas fraction increases toward lower mass, galaxies with M_baryon ∼ 10¹⁰ M_☉ would shift to lower stellar masses, creating the observed dip. This would indicate a change in star formation efficiency, perhaps linked to supernovae feedback becoming much more efficient below ∼10¹⁰ M_☉. Therefore, we investigate whether the dip is present in the baryonic (stars+gas) mass function. Alternatively, the dip could be created by an enhancement of the galaxy assembly rate at ∼10¹¹ M_☉, a phenomenon that naturally arises if the baryon fraction peaks at M_halo ∼ 10¹² M_☉. In this scenario, galaxies occupying the bump around M_* would be identified with central galaxies and the second fainter component of the mass function having a steep faint-end slope with satellite galaxies. The low-mass end of the blue and total mass functions exhibit a steeper slope than has been detected in previous work that may increasingly approach the halo mass function value of −2. While the dip feature is apparent in the total mass function at all redshifts, it appears to shift from the blue to the red population, likely as a result of transforming high-mass blue galaxies into red ones. At the same time, we detect a drastic upturn in the number of low-mass red galaxies. Their increase with time seems to reflect a decrease in the number of blue systems and so we tentatively associate them with satellite dwarf (spheroidal) galaxies that have undergone quenching due to environmental processes.

This paper presents a numerical study over a wide parameter space of the likelihood of dynamical bar-mode instability in differentially rotating magnetized neutron stars. The innovative aspect of this study is the incorporation of magnetic fields in such a context, which have thus far been neglected in the purely hydrodynamical simulations available in the literature. The investigation uses the Cosmos++ code which allows us to perform three-dimensional simulations on a cylindrical grid at high resolution. A sample of Newtonian magnetohydrodynamical simulations starting from a set of models previously analyzed by other authors without magnetic fields has been performed, providing estimates of the effects of magnetic fields on the dynamical bar-mode deformation of rotating neutron stars. Overall, our results suggest that the effect of magnetic fields is not likely to be very significant in realistic configurations. Only in the most extreme cases are the magnetic fields able to suppress growth of the bar mode.

X-ray afterglow light curves have been collected for over 400 Swift gamma-ray bursts (GRBs) with nearly half of them having X-ray flares superimposed on the regular afterglow decay. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge, and spread, producing prompt emission and X-ray flares. We pay special attention to the time history of central engine activity, internal shocks, and observed flares, but do not calculate the shock dynamics and radiation processes in detail. Using the empirical E_p–E_iso (Amati) relation with an assumed Band function spectrum for each collision and an empirical flare temporal profile, we calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary central engine activity and compare the model results with the observational data. We show that the observed X-ray flare phenomenology can be explained within the internal shock model. The number, width, and occurring time of flares are then used to diagnose the central engine activity, putting constraints on the energy, ejection time, width, and number of ejected shells. We find that the observed X-ray flare time history generally reflects the time history of the central engine, which reactivates multiple times after the prompt emission phase with progressively reduced energy. The same shell model predicts an external shock X-ray afterglow component, which has a shallow decay phase due to the initial pile-up of shells onto the blast wave. However, the predicted X-ray afterglow is too bright as compared with the observed flux level, unless _e is as low as 10⁻³.

Long gamma-ray bursts (GRBs) have been suggested to occur preferentially in low-metallicity environment. We discuss the possibility and theoretical aspects of using Lyα emission properties of long GRB host galaxies as a metallicity indicator of high-redshift GRB environments, where direct metallicity measurements are not easy. We propose to use the fraction of Lyα emitters (LAEs) in long GRB host galaxies as a function of UV luminosity, which can be compared with star formation rate weighted LAE fraction of Lyman break galaxies as the standard in the case of no metallicity dependence. There are two important effects of metallicity dependence of long GRB rate to change the LAE fraction of host galaxies. One is the enhancement of intrinsic Lyα equivalent width (EW) by stronger ionizing UV luminosity of low-metallicity stellar population, and the other is extinction by interstellar dust to change the observable EW. Based on a latest theoretical model of LAEs that reproduce observations, we argue that the latter is likely to work in the opposite direction to the former, i.e., to decrease LAE fraction if GRBs preferentially occur in low-metallicity environments, because of the clumpy interstellar medium effect. The high LAE fraction of GRB host galaxies indicated by observations is quantitatively explained by the LAE model if GRBs occur when Z ≲ 0.1 Z_☉, although this result is still indicative because of the limited statistics and theoretical uncertainties. This result demonstrates that the LAE statistics of GRB hosts may give us useful information in the future.

The Smith Cloud is a massive system of metal-poor neutral and ionized gas (M_gas ≳ 2 × 10⁶ M_☉) that is presently moving at high velocity (V_GSR≈ 300 km s⁻¹) with respect to the Galaxy at a distance of 12 kpc from the Sun. The kinematics of the cloud's cometary tail indicates that the gas is in the process of accretion onto the Galaxy, as first discussed by Lockman et al. Here, we re-investigate the cloud's orbit by considering the possibility that the cloud is confined by a dark matter halo. This is required for the cloud to survive its passage through the Galactic corona. We consider three possible models for the dark matter halo (Navarro–Frenk–White (NFW), Einasto, and Burkert) including the effects of tidal disruption and ram pressure stripping during the cloud's infall onto and passage through the Galactic disk. For the NFW and Einasto dark matter models, we are able to determine reasonable initial conditions for the Smith Cloud, although this is only marginally possible with the Burkert model. For all three models, the progenitor had an initial (gas+dark matter) mass that was an order-of-magnitude higher than inferred today. In agreement with Lockman et al., the cloud appears to have punched through the disk ≈70 Myr ago. For our most successful models, the baryon-to-dark matter ratio is fairly constant during an orbital period but drops by a factor of 2–5 after transiting the disk. The cloud appears to have only marginally survived its transit and is unlikely to retain its integrity during the next transit ≈ 30 Myr from now.

Assuming that density waves trigger star formation, and that young stars preserve the velocity components of the molecular gas where they are born, we analyze the effects that non-circular gas orbits have on color gradients across spiral arms. We try two approaches, one involving semianalytical solutions for spiral shocks, and another with magnetohydrodynamic (MHD) numerical simulation data. We find that, if non-circular motions are ignored, the comparison between observed color gradients and stellar population synthesis models would in principle yield pattern speed values that are systematically too high for regions inside corotation, with the difference between the real and the measured pattern speeds increasing with decreasing radius. On the other hand, image processing and pixel averaging result in systematically lower measured spiral pattern speed values, regardless of the kinematics of stellar orbits. The net effect is that roughly the correct pattern speeds are recovered, although the trend of higher measured Ω_p at lower radii (as expected when non-circular motions exist but are neglected) should still be observed. We examine the Martínez-García et al. photometric data and confirm that this is indeed the case. The comparison of the size of the systematic pattern speed offset in the data with the predictions of the semianalytical and MHD models corroborates that spirals are more likely to end at outer Lindblad resonance, as these authors had already found.

We study the propagation, reflection, and turbulent dissipation of Alfvén waves in coronal holes and the solar wind. We start with the Heinemann–Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium with a background flow parallel to the background magnetic field. Following the approach of Dmitruk et al., we model the nonlinear terms in these equations using a simple phenomenology for the cascade and dissipation of wave energy and assume that there is much more energy in waves propagating away from the Sun than waves propagating toward the Sun. We then solve the equations analytically for waves with periods of hours and longer to obtain expressions for the wave amplitudes and turbulent heating rate as a function of heliocentric distance. We also develop a second approximate model that includes waves with periods of roughly one minute to one hour, which undergo less reflection than the longer-period waves, and compare our models to observations. Our models generalize the phenomenological model of Dmitruk et al. by accounting for the solar wind velocity, so that the turbulent heating rate can be evaluated from the coronal base out past the Alfvén critical point—that is, throughout the region in which most of the heating and acceleration occurs. The simple analytical expressions that we obtain can be used to incorporate Alfvén-wave reflection and turbulent heating into fluid models of the solar wind.

One proposed mechanism for heating the solar wind, from close to the Sun to beyond ∼10 AU, invokes low-frequency, oblique, Alfvén-wave turbulence. Because small-scale oblique Alfvén waves (kinetic Alfvén waves, KAWs) are compressive, the measured density fluctuations in the solar wind place an upper limit on the amplitude of KAWs and hence an upper limit on the rate at which the solar wind can be heated by low-frequency, Alfvénic turbulence. We evaluate this upper limit for both coronal holes at 5 R_☉ and the near-Earth solar wind. At both locations, the upper limit we find is consistent with models in which the solar wind is heated by low-frequency Alfvénic turbulence. At 1 AU, the upper limit on the turbulent heating rate derived from the measured density fluctuations is within a factor of 2 of the measured solar-wind heating rate. Thus, if low-frequency Alfvénic turbulence is the primary mechanism for heating the near-Earth solar wind, KAWs must be one of the dominant sources of solar-wind density fluctuations at frequencies ∼1 Hz. We also present a simple argument for why density-fluctuation measurements do appear to rule out models in which coronal holes are heated by non-turbulent high-frequency waves ("sweeping"), but are compatible with heating by low-frequency Alfvénic turbulence.

We present an integral field spectroscopic study of the central 2 × 2 kpc² of the blue compact dwarf galaxy Mrk 409, observed with the Potsdam MultiAperture Spectrophotometer (PMAS). This study focuses on the morphology, two-dimensional chemical abundance pattern, excitation properties, and kinematics of the ionized interstellar medium in the starburst component. We also investigate the nature of the extended ring of ionized gas emission surrounding the bright nuclear starburst region of Mrk 409. PMAS spectra of selected regions along the ring, interpreted with evolutionary and population synthesis models, indicate that their ionized emission is mainly due to a young stellar population with a total mass of ∼1.5 × 10⁶M_☉, which started forming almost coevally ∼10 Myr ago. This stellar component is likely confined to the collisional interface of a spherically expanding, starburst-driven super-bubble with denser, swept-up ambient gas, ∼600 pc away from the central starburst nucleus. The spectroscopic properties of the latter imply a large extinction (C_Hβ>0.9), and the presence of an additional non-thermal ionization source, most likely a low-luminosity active galactic nucleus. Mrk 409 shows a relatively large oxygen abundance (12 + log(O/H) ∼ 8.4) and no chemical abundance gradients out to R ∼ 600 pc. The ionized gas kinematics displays an overall regular rotation on a northwest–southeast axis, with a maximum velocity of 60 km s⁻¹; the total mass inside the star-forming ring is about 1.4 × 10⁹ M_☉.

The incidence and properties of active galactic nuclei (AGNs) in the field, groups, and clusters can provide new information about how these objects are triggered and fueled, similar to how these environments have been employed to study galaxy evolution. We have obtained new XMM-Newton observations of seven X-ray selected groups and poor clusters with 0.02 < z < 0.06 for comparison with previous samples that mostly included rich clusters and optically selected groups. Our final sample has ten groups and six clusters in this low-redshift range (split at a velocity dispersion of σ = 500 kms⁻¹). We find that the X-ray selected AGN fraction increases from f_A(L_X ⩾ 10⁴¹;  M_R ⩽ M*_R + 1) = 0.047^+0.023_−0.016 in clusters to 0.091^+0.049_−0.034 for the groups (85% significance), or a factor of 2, for AGN above an 0.3–8 keV X-ray luminosity of 10⁴¹ergs⁻¹ hosted by galaxies more luminous than M*_R + 1. The trend is similar, although less significant, for a lower-luminosity host threshold of M_R = −20 mag. For many of the groups in the sample, we have also identified AGN via standard emission-line diagnostics and find that these AGNs are nearly disjoint from the X-ray selected AGN. Because there are substantial differences in the morphological mix of galaxies between groups and clusters, we have also measured the AGN fraction for early-type galaxies alone to determine if the differences are directly due to environment, or indirectly due to the change in the morphological mix. We find that the AGN fraction in early-type galaxies is also lower in clusters f_A,n⩾2.5(L_X ⩾ 10⁴¹;  M_R ⩽ M*_R + 1) = 0.048^+0.028_−0.019 compared to 0.119^+0.064_−0.044 for the groups (92% significance), a result consistent with the hypothesis that the change in AGN fraction is directly connected to environment.

We report the detection in Ks-band of the secondary eclipse of the hot Jupiter CoRoT-1b from time series photometry with the ARC 3.5 m telescope at Apache Point Observatory. The eclipse shows a depth of 0.336 ± 0.042% and is centered at phase 0.5022^+0.0023_−0.0027, consistent with a zero eccentricity orbit (e cos ω = 0.0035^+0.0036_−0.0042). We perform the first optical to near-infrared multi-band photometric analysis of an exoplanet's atmosphere and constrain the reflected and thermal emissions by combining our result with the recent 0.6, 0.71, and 2.09 μm secondary eclipse detections by Snellen et al., Gillon et al., and Alonso et al. Comparing the multi-wavelength detections to state-of-the-art radiative-convective chemical-equilibrium atmosphere models, we find the near-infrared fluxes difficult to reproduce. The closest blackbody-based and physical models provide the following atmosphere parameters: a temperature T = 2460⁺⁸⁰₋₁₆₀ K; a very low Bond albedo A_B = 0.000^+0.081_−0.000; and an energy redistribution parameter P_n = 0.1, indicating a small but nonzero amount of heat transfer from the day to nightside. The best physical model suggests a thermal inversion layer with an extra optical absorber of opacity κ_e = 0.05 cm² g⁻¹, placed near the 0.1 bar atmospheric pressure level. This inversion layer is located 10 times deeper in the atmosphere than the absorbers used in models to fit mid-infrared Spitzer detections of other irradiated hot Jupiters.

We report on recent XMM-Newton observations, archival radio continuum and CO data, and spectral energy distribution (SED) modeling of the unidentified Galactic plane source HESS J1708−410. No significant extended X-ray emission is observed, and we place an upper limit of 3.2 × 10⁻¹³ erg cm^-2 s⁻¹ in the 2–4 keV range for the region of TeV emission. Molonglo Galactic Plane Survey data are used to place an upper limit of 0.27 Jy at 843 MHz for the source, with a 2.4 GHz limit of 0.4 Jy from the Parkes survey of the southern Galactic plane. ¹²CO (J 1 → 0) data of this region indicates a plausible distance of 3 kpc for HESS J1708−410. SED modeling of both the HESS detection and flux upper limits offer useful constraints on the emission mechanisms, magnetic field, injection spectrum, and ambient medium surrounding this source.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) operated successfully during a 250 hr flight over Antarctica in 2006 December (BLAST06). As part of the calibration and pointing procedures, the red hypergiant star VY CMa was observed and used as the primary calibrator. Details of the overall BLAST06 calibration procedure are discussed. The 1σ uncertainty on the absolute calibration is accurate to 9.5%, 8.7%, and 9.2% at the 250, 350, and 500 μm bands, respectively. The errors are highly correlated between bands resulting in much lower errors for the derived shape of the 250–500 μm continuum. The overall pointing error is < 5'' rms for the 36'', 42'', and 60'' beams. The performance of optics and pointing systems is discussed.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has made 1 deg², deep, confusion-limited maps at three different bands, centered on the Great Observatories Origins Deep Survey South Field. By calculating the covariance of these maps with catalogs of 24 μm sources from the Far-Infrared Deep Extragalactic Legacy Survey, we have determined that the total submillimeter intensities are 8.60 ± 0.59, 4.93 ± 0.34, and 2.27 ± 0.20 nW m⁻² sr⁻¹ at 250, 350, and 500 μm, respectively. These numbers are more precise than previous estimates of the cosmic infrared background (CIB) and are consistent with 24 μm-selected galaxies generating the full intensity of the CIB. We find that the fraction of the CIB that originates from sources at z ⩾ 1.2 increases with wavelength, with 60% from high-redshift sources at 500 μm. At all BLAST wavelengths, the relative intensity of high-z sources is higher for 24 μm-faint sources than that for 24 μm-bright sources. Galaxies identified as active galactic nuclei (AGNs) by their Infrared Array Camera colors are 1.6–2.6 times brighter than the average population at 250–500 μm, consistent with what is found for X-ray-selected AGNs. BzK-selected galaxies are found to be moderately brighter than typical 24 μm-selected galaxies in the BLAST bands. These data provide high-precision constraints for models of the evolution of the number density and intensity of star-forming galaxies at high redshift.

We directly measure redshift evolution in the mean physical properties (far-infrared luminosity, temperature, and mass) of the galaxies that produce the cosmic infrared background (CIB), using measurements from the Balloon-borne Large Aperture Submillimeter Telescope (BLAST), and Spitzer which constrain the CIB emission peak. This sample is known to produce a surface brightness in the BLAST bands consistent with the full CIB, and photometric redshifts are identified for all of the objects. We find that most of the 70 μm background is generated at z ≲ 1 and the 500 μm background generated at z ≳ 1. A significant growth is observed in the mean luminosity from ∼10⁹–10¹²L_☉, and in the mean temperature by 10 K, from redshifts 0 < z < 3. However, there is only weak positive evolution in the comoving dust mass in these galaxies across the same redshift range. We also measure the evolution of the far-infrared luminosity density, and the star formation rate history for these objects, finding good agreement with other infrared studies up to z ∼ 1, exceeding the contribution attributed to optically selected galaxies.

We describe the application of a statistical method to estimate submillimeter galaxy number counts from confusion-limited observations by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST). Our method is based on a maximum likelihood fit to the pixel histogram, sometimes called "P(D)," an approach which has been used before to probe faint counts, the difference being that here we advocate its use even for sources with relatively high signal-to-noise ratios. This method has an advantage over standard techniques of source extraction in providing an unbiased estimate of the counts from the bright end down to flux densities well below the confusion limit. We specifically analyze BLAST observations of a roughly 10 deg² map centered on the Great Observatories Origins Deep Survey South field. We provide estimates of number counts at the three BLAST wavelengths 250, 350, and 500 μm; instead of counting sources in flux bins we estimate the counts at several flux density nodes connected with power laws. We observe a generally very steep slope for the counts of about −3.7 at 250 μm, and −4.5 at 350 and 500 μm, over the range ∼0.02–0.5 Jy, breaking to a shallower slope below about 0.015 Jy at all three wavelengths. We also describe how to estimate the uncertainties and correlations in this method so that the results can be used for model-fitting. This method should be well suited for analysis of data from the Herschel satellite.

We detect correlations in the cosmic far-infrared background due to the clustering of star-forming galaxies in observations made with the Balloon-borne Large Aperture Submillimeter Telescope, at 250, 350, and 500 μm. We perform jackknife and other tests to confirm the reality of the signal. The measured correlations are well fitted by a power law over scales of 5'–25', with ΔI/I = 15.1% ± 1.7%. We adopt a specific model for submillimeter sources in which the contribution to clustering comes from sources in the redshift ranges 1.3 ⩽ z ⩽ 2.2, 1.5 ⩽ z ⩽ 2.7,  and 1.7 ⩽ z ⩽ 3.2, at 250, 350, and 500 μm, respectively. With these distributions, our measurement of the power spectrum, P(k_θ), corresponds to linear bias parameters, b = 3.8 ± 0.6, 3.9 ± 0.6, and 4.4 ± 0.7, respectively. We further interpret the results in terms of the halo model, and find that at the smaller scales, the simplest halo model fails to fit our results. One way to improve the fit is to increase the radius at which dark matter halos are artificially truncated in the model, which is equivalent to having some star-forming galaxies at z ⩾ 1 located in the outskirts of groups and clusters. In the context of this model, we find a minimum halo mass required to host a galaxy is log(M_min/M_☉) = 11.5^+0.4_−0.1, and we derive effective biases b_eff = 2.2 ± 0.2, 2.4 ± 0.2, and 2.6 ± 0.2, and effective masses $\mathrm{log}(M_{\mathrm{\rm eff}}/M_{\odot }) = 12.9 \pm 0.3$, 12.8 ± 0.2, and 12.7 ± 0.2, at 250, 350 and 500 μm, corresponding to spatial correlation lengths of r₀ = 4.9, 5.0, and $5.2 \pm 0.7 h^{-1} \rm Mpc$, respectively. Finally, we discuss implications for clustering measurement strategies with Herschel and Planck.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has recently surveyed ≃8.7 deg² centered on Great Observatories Origins Deep Survey-South at 250, 350, and 500 μm. In Dye et al., we presented the catalog of sources detected at 5σ in at least one band in this field and the probable counterparts to these sources in other wavebands. In this paper, we present the results of a redshift survey in which we succeeded in measuring redshifts for 82 of these counterparts. The spectra show that the BLAST counterparts are mostly star-forming galaxies but not extreme ones when compared to those found in the Sloan Digital Sky Survey. Roughly one quarter of the BLAST counterparts contain an active nucleus. We have used the spectroscopic redshifts to carry out a test of the ability of photometric redshift methods to estimate the redshifts of dusty galaxies, showing that the standard methods work well even when a galaxy contains a large amount of dust. We have also investigated the cases where there are two possible counterparts to the BLAST source, finding that in at least half of these there is evidence that the two galaxies are physically associated, either because they are interacting or because they are in the same large-scale structure. Finally, we have made the first direct measurements of the luminosity function in the three BLAST bands. We find strong evolution out to z = 1, in the sense that there is a large increase in the space density of the most luminous galaxies. We have also investigated the evolution of the dust-mass function, finding similar strong evolution in the space density of the galaxies with the largest dust masses, showing that the luminosity evolution seen in many wavebands is associated with an increase in the reservoir of interstellar matter in galaxies.

Over the course of two flights, the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) made resolved maps of seven nearby (<25 Mpc) galaxies at 250, 350, and 500 μm. During its 2005 June flight from Sweden, BLAST observed a single nearby galaxy, NGC 4565. During the 2006 December flight from Antarctica, BLAST observed the nearby galaxies NGC 1097, NGC 1291, NGC 1365, NGC 1512, NGC 1566, and NGC 1808. We fit physical dust models to a combination of BLAST observations and other available data for the galaxies observed by Spitzer. We fit a modified blackbody to the remaining galaxies to obtain total dust mass and mean dust temperature. For the four galaxies with Spitzer data, we also produce maps and radial profiles of dust column density and temperature. We measure the fraction of BLAST detected flux originating from the central cores of these galaxies and use this to calculate a "core fraction," an upper limit on the "active galactic nucleus fraction" of these galaxies. We also find our resolved observations of these galaxies give a dust mass estimate 5–19 times larger than an unresolved observation would predict. Finally, we are able to use these data to derive a value for the dust mass absorption coefficient of κ = 0.29 ± 0.03 m² kg⁻¹ at 250 μm. This study is an introduction to future higher-resolution and higher-sensitivity studies to be conducted by Herschel and SCUBA-2.

We present first results from an unbiased 50 deg² submillimeter Galactic survey at 250, 350, and 500 μm from the 2006 flight of the Balloon-borne Large Aperture Submillimeter Telescope. The map has resolution ranging from 36'' to 60'' in the three submillimeter bands spanning the thermal emission peak of cold starless cores. We determine the temperature, luminosity, and mass of more than 1000 compact sources in a range of evolutionary stages and an unbiased statistical characterization of the population. From comparison with C¹⁸O data, we find the dust opacity per gas mass, κr= 0.16 cm² g⁻¹ at 250 μm, for cold clumps. We find that 2% of the mass of the molecular gas over this diverse region is in cores colder than 14 K, and that the mass function for these cold cores is consistent with a power law with index α = −3.22 ± 0.14 over the mass range 14 M_☉ < M < 80 M_☉. Additionally, we infer a mass-dependent cold core lifetime of t_c(M) = 4 × 10⁶(M/20 M_☉)^−0.9 yr—longer than what has been found in previous surveys of either low or high-mass cores, and significantly longer than free fall or likely turbulent decay times. This implies some form of non-thermal support for cold cores during this early stage of star formation.

The Balloon-borne Large-Aperture Submillimeter Telescope (BLAST) carried out a 250, 350, and 500 μm survey of the galactic plane encompassing the Vela Molecular Ridge, with the primary goal of identifying the coldest dense cores possibly associated with the earliest stages of star formation. Here, we present the results from observations of the Vela-D region, covering about 4 deg², in which we find 141 BLAST cores. We exploit existing data taken with the Spitzer MIPS, IRAC, and SEST–SIMBA instruments to constrain their (single-temperature) spectral energy distributions, assuming a dust emissivity index β = 2.0. This combination of data allows us to determine the temperature, luminosity, and mass of each BLAST core, and also enables us to separate starless from protostellar sources. We also analyze the effects that the uncertainties on the derived physical parameters of the individual sources have on the overall physical properties of starless and protostellar cores, and we find that there appear to be a smooth transition from the pre- to the protostellar phase. In particular, for protostellar cores we find a correlation between the MIPS24 flux, associated with the central protostar, and the temperature of the dust envelope. We also find that the core mass function of the Vela-D cores has a slope consistent with other similar (sub)millimeter surveys.

The wide-band Suzaku spectra of the black hole (BH) binary GX 339−4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within ∼3' of the image center) and telemetry saturation of the X-ray Imaging Spectrometer (XIS) data were carefully considered. The source was detected up to ∼300 keV, with an unabsorbed 0.5–200 keV luminosity of 3.8 × 10³⁸ erg s⁻¹ at 8 kpc. The spectrum can be approximated by a power law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2' of the image center, the Fe K line appeared extremely broad, suggesting a high BH spin as already reported by Miller et al. based on the same Suzaku data and other CCD data. When the XIS data accumulation is further limited to >3' to avoid event pileup, the Fe K profile becomes narrower, and a marginally better solution appears which suggests that the inner disk radius is 5–14 times the gravitational radius (1σ), though a maximally spinning BH is still allowed by the data at the 90% confidence level. Consistently, the optically thick accretion disk is inferred to be truncated at a radius 5–32 times the gravitational radius. Thus, the Suzaku data allow an alternative explanation without invoking a rapidly spinning BH. This inference is further supported by the disk radius measured previously in the High/Soft state.

Two recent papers (Ghez et al. 2008; Gillessen et al. 2009) have estimated the mass of and the distance to the massive black hole (MBH) in the center of the Milky Way using stellar orbits. The two astrometric data sets are independent and yielded consistent results, even though the measured positions do not match when simply overplotting the two sets. In this Letter, we show that the two sets can be brought to excellent agreement with each other when we allow for a small offset in the definition of the reference frame of the two data sets. The required offsets in the coordinates and velocities of the origin of the reference frames are consistent with the uncertainties given in Ghez et al. The so-combined data set allows for a moderate improvement of the statistical errors of the mass of and the distance to Sgr A*, but the overall accuracies of these numbers are dominated by systematic errors and the long-term calibration of the reference frame. We obtain R₀ = 8.28 ± 0.15|_stat ±  0.29|_sys kpc and M_MBH = 4.30 ±  0.20|_stat ±  0.30|_sys × 10⁶ M_☉ as best estimates from a multi-star fit.

We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is Δm₁₅(B) = 0.65 ± 0.03, which is one of the slowest among SNe Ia. The peak V-band absolute magnitude is estimated to be M_V = −19.90 ± 0.15 mag if no host extinction is assumed. It reaches M_V = −20.19 ± 0.19 mag if we assume the host extinction of A_V = 0.29 mag. SN 2009dc belongs to the most luminous class of SNe Ia, like SNe 2003fg and 2006gz. Our JHK_s-band photometry shows that this SN is also one of the most luminous SNe Ia in near-infrared wavelengths. We estimate the ejected ⁵⁶Ni mass of 1.2 ± 0.3 M_☉ for the no host extinction case (and of 1.6 ± 0.4 M_☉ for the host extinction of A_V = 0.29 mag). The C ii λ6580 absorption line remains visible until a week after the maximum brightness, in contrast to its early disappearance in SN 2006gz. The line velocity of Si ii λ6355 is about 8000 km s⁻¹ around the maximum, being considerably slower than that of SN 2006gz. The velocity of the C ii line is similar to or slightly less than that of the Si ii line around the maximum. The presence of the carbon line suggests that the thick unburned C+O layer remains after the explosion. Spectropolarimetric observations by Tanaka et al. indicate that the explosion is nearly spherical. These observational facts suggest that SN 2009dc is a super-Chandrasekhar mass SN Ia.

We present the discovery of a brown dwarf or possible planet at a projected separation of 19 = 29 AU around the star GJ 758, placing it between the separations at which substellar companions are expected to form by core accretion (∼5 AU) or direct gravitational collapse (typically ≳100 AU). The object was detected by direct imaging of its thermal glow with Subaru/HiCIAO. At 10–40 times the mass of Jupiter and a temperature of 550–640 K, GJ 758 B constitutes one of the few known T-type companions, and the coldest ever to be imaged in thermal light around a Sun-like star. Its orbit is likely eccentric and of a size comparable to Pluto's orbit, possibly as a result of gravitational scattering or outward migration. A candidate second companion is detected at 12 at one epoch.

Hundreds of radar-dark patches interpreted as lakes have been discovered in the north and south polar regions of Titan. We have estimated the composition of these lakes by using the direct abundance measurements from the Gas Chromatograph Mass Spectrometer aboard the Huygens probe and recent photochemical models based on the vertical temperature profile derived by the Huygens Atmospheric Structure Instrument. Thermodynamic equilibrium is assumed between the atmosphere and the lakes, which are also considered nonideal solutions. We find that the main constituents of the lakes are ethane (C₂H₆) (∼76%–79%), propane (C₃H₈) (∼7%–8%), methane (CH₄) (∼5%–10%), hydrogen cyanide (HCN) (∼2%–3%), butene (C₄H₈) (∼1%), butane (C₄H₁₀) (∼1%), and acetylene (C₂H₂) (∼1%). The calculated composition of lakes is then substantially different from what has been expected from models elaborated prior to the exploration of Titan by the Cassini–Huygens spacecraft.

Using the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) coronagraph, we have obtained high-contrast 2.0 μm imaging polarimetry and 1.1 μm imaging of the circumstellar disk around AB Aurigae on angular scales of 03–3'' (40–550 AU). Unlike previous observations, these data resolve the disk in both total and polarized intensity, allowing accurate measurement of the spatial variation of polarization fraction across the disk. Using these observations, we investigate the apparent "gap" in the disk reported by Oppenheimer et al.. In polarized intensity, the NICMOS data closely reproduce the morphology seen by Oppenheimer et al., yet in total intensity we find no evidence for a gap in either our 1.1 or 2.0 μm images. We find instead that region has lower polarization fraction, without a significant decrease in total scattered light, consistent with expectations for backscattered light on the far side of an inclined disk. Radiative transfer models demonstrate this explanation fits the observations. Geometrical scattering effects are entirely sufficient to explain the observed morphology without any need to invoke a gap or a protoplanet at that location.

Plasma jet formation was observed in counterstreaming plasmas in a laboratory experiment. In order to model an ambient plasma of astrophysical jets, the counterstreaming plasmas were created by irradiating a double CH-plane target with a high-power laser system. Since the mean free paths of the ions in terms of the counterstreaming motion were larger than the scale length of the experiment, the two-stream interaction of the plasmas was essentially collisionless. The time evolution of the jet collimation was obtained over several shots with different timing by shadowgraphy. When a single CH-plane target was irradiated, no jet collimation was observed. The counterstreaming plasma as an ambient plasma is essential for the jet plasma to collimate.

We report the discovery with Fermi/LAT of γ-ray emission from three radio-loud narrow-line Seyfert 1 galaxies: PKS 1502+036 (z = 0.409), 1H 0323+342 (z = 0.061), and PKS 2004 − 447 (z = 0.24). In addition to PMN J0948+0022 (z = 0.585), the first source of this type to be detected in γ rays, they may form an emerging new class of γ-ray active galactic nuclei (AGNs). These findings can have strong implications on our knowledge about relativistic jets and the unified model of the AGN.

We report the detection of extended emission around the anomalous X-ray pulsar 1E1547.0-5408 using archival data of the Chandra X-ray satellite. The extended emission consists of an inner part, with an extent of 45'', and an outer part with an outer radius of 29, which coincides with a supernova remnant shell previously detected in the radio. We argue that the extended emission in the inner part is the result of a pulsar wind nebula (PWN), which would be the first detected PWN around a magnetar candidate. Its ratio of X-ray luminosity versus pulsar spin-down power is comparable to that of other young PWNe, but its X-ray spectrum is steeper than most PWNe. We discuss the importance of this source in the context of magnetar evolution.

Is the turbulence in cluster-forming regions internally driven by stellar outflows or the consequence of a large-scale turbulent cascade? We address this question by studying the turbulent energy spectrum in NGC 1333. Using synthetic ¹³CO maps computed with a snapshot of a supersonic turbulence simulation, we show that the velocity coordinate spectrum method of Lazarian & Pogosyan provides an accurate estimate of the turbulent energy spectrum. We then apply this method to the ¹³CO map of NGC 1333 from the COMPLETE database. We find that the turbulent energy spectrum is a power law, E(k) ∝ k^−β, in the range of scales 0.06 pc ⩽ℓ ⩽ 1.5 pc, with slope β = 1.85 ± 0.04. The estimated energy injection scale of stellar outflows in NGC 1333 is ℓ_inj ≈ 0.3 pc, well resolved by the observations. There is no evidence of the flattening of the energy spectrum above the scale ℓ_inj predicted by outflow-driven simulations and analytical models. The power spectrum of integrated intensity is also a nearly perfect power law in the range of scales 0.16 pc <ℓ< 7.9 pc, with no feature above ℓ_inj. We conclude that the observed turbulence in NGC 1333 does not appear to be driven primarily by stellar outflows.

It is widely accepted that magnetic reconnection releases a large amount of energy during solar flares. Studies of reconnection usually assume that the length scale over which the global (macroscopic) magnetic field reverses is identical to the thickness of the reconnection site. However, in spatially extended high-Lundquist number plasmas such as the solar corona, this scenario is untenable; the reconnection site is microscopic and embedded inside the macroscopic current set up by global fields. We use numerical simulations and scaling arguments to show that embedded effects on reconnection could have a profound influence on energy storage before a flare. From large-scale high-Lundquist number resistive magnetohydrodynamics simulations of reconnection with a diffusion region on a much smaller scale than the macroscopic current sheet, we find that the generation of secondary islands is governed by the local magnetic field immediately upstream of the diffusion region rather than the (potentially much larger) global field. This diminishes the production of secondary islands and leads to a thicker diffusion region than those predicted using the global field strength. Such considerations are crucial for understanding the onset of solar eruptions and how energy accumulates before such eruptions. We argue that if reconnection with secondary islands is fast, the energy storage times before an eruption are too small to explain observations. If reconnection with secondary islands remains slow, embedded effects cause the diffusion region to begin far wider than kinetic scales, so energy storage before a flare can occur while collisional (Sweet–Parker) reconnection with secondary islands proceeds.

We present Advanced Camera for Surveys observations of MACS J1149.5+2223, an X-ray luminous galaxy cluster at z = 0.544 discovered by the Massive Cluster Survey. The data reveal at least seven multiply imaged galaxies, three of which we have confirmed spectroscopically. One of these is a spectacular face-on spiral galaxy at z = 1.491, the four images of which are gravitationally magnified by 8 ≲ μ ≲ 23. We identify this as an L^⋆ (M_B ≃ −20.7), disk-dominated (B/T ≲ 0.5) galaxy, forming stars at ∼6 M_☉ yr⁻¹. We use a robust sample of multiply imaged galaxies to constrain a parameterized model of the cluster mass distribution. In addition to the main cluster dark matter halo and the bright cluster galaxies, our best model includes three galaxy-group-sized halos. The relative probability of this model is P(N_halo = 4)/P(N_halo < 4) ⩾ 10¹² where N_halo is the number of cluster/group-scale halos. In terms of sheer number of merging cluster/group-scale components, this is the most complex strong-lensing cluster core studied to date. The total cluster mass and fraction of that mass associated with substructures within R ⩽ 500 kpc, are measured to be M_tot = (6.7 ± 0.4) × 10¹⁴ M_☉ and f_sub = 0.25 ± 0.12, respectively. Our model also rules out recent claims of a flat density profile at ≳7σ confidence, thus highlighting the critical importance of spectroscopic redshifts of multiply imaged galaxies when modeling strong-lensing clusters. Overall our results attest to the efficiency of X-ray selection in finding the most powerful cluster lenses, including complicated merging systems.

We use a modified three-dimensional outer gap model to explain the features of the pulsed emission and spectra of the Crab pulsar from X-ray to above 25 GeV regimes. In such an outer gap model, the phase-averaged spectra below ∼1 GeV are mainly produced through the synchrotron self-Compton mechanism, and the spectrum above ∼1 GeV are due to the survival curvature photons. Our results show that (1) the observed phase-averaged spectrum from X-rays to γ-rays including the Fermi LAT and MAGIC data can be reproduced well, and (2) the basic properties of both the observed phase-dependent spectra of both X-ray and γ-ray up to >25 GeV can be interpreted in this model.

Pyroxenes and olivines are the dominant crystalline silicates observed in protoplanetary disks. Recent spectral observations from the Spitzer Space Telescope indicate that the abundance of olivine, generally associated with silica polymorphs, relative to pyroxene is higher in the outer cold part of the disk than in the inner warmer part. The interpretation of these unexpected results requires a comprehensive knowledge of the thermal processing of Mg-rich silicate dust. In this respect, amorphous analogs were thermally annealed to identify microscopic crystallization mechanisms. We show that pyroxenes are not produced in significant proportions below the glass transition temperature of the amorphous precursor. The annealing of amorphous enstatite leads to a mineralogical assemblage dominated by forsterite, with only minute amounts of pyroxenes at temperatures as high as the glass transition temperature of enstatite (1050 K). The decoupling of cation mobility in amorphous silicates, favors the crystallization of the most Mg-enriched silicates. These results are consistent with Spitzer observations of silicate dust and also with the documented mineralogy of presolar silicates, making the low-temperature annealing a likely formation process for these objects. Based on these laboratory experiments and Spitzer observations, it appears that the reported zoned mineralogy may directly records and calibrates the thermal gradient at the scale of protoplanetary disks.

We study cosmic-ray acceleration in a supernova remnant (SNR) and the escape from it. We model nonthermal particle and photon spectra for the hidden SNR in the open cluster Westerlund 2, and the old-age mixed-morphology SNR W 28. We assume that the SNR shock propagates in a low-density cavity, which is created and heated through the activities of the progenitor stars and/or previous supernova explosions. We indicate that the diffusion coefficient for cosmic rays around the SNRs is less than ∼1% of that away from them. We compare our predictions with the gamma-ray spectra of molecular clouds illuminated by the cosmic rays (Fermi and H.E.S.S.). We found that the spectral indices of the particles are ∼2.3. This may be because the particles were accelerated at the end of the Sedov phase, and because energy-dependent escape and propagation of particles did not much affect the spectrum.

We study the evolution of black holes (BHs) on the M_BH–σ and M_BH–M_bulge planes as a function of time in disk galaxies undergoing mergers. We begin the simulations with the progenitor BH masses being initially below (Δlog M_BH,i ∼ −2), on (Δlog M_BH,i ∼ 0), and above (Δlog M_BH,i ∼ 0.5) the observed local relations. The final relations are rapidly established after the final coalescence of the galaxies and their BHs. Progenitors with low initial gas fractions (f_gas = 0.2) starting below the relations evolve onto the relations (Δlog M_BH,f ∼ −0.18), progenitors on the relations stay there (Δlog M_BH,f ∼ 0), and finally progenitors above the relations evolve toward the relations, but still remain above them (Δlog M_BH,f ∼ 0.35). Mergers in which the progenitors have high initial gas fractions (f_gas = 0.8) evolve above the relations in all cases (Δlog M_BH,f ∼ 0.5). We find that the initial gas fraction is the prime source of scatter in the observed relations, dominating over the scatter arising from the evolutionary stage of the merger remnants. The fact that BHs starting above the relations do not evolve onto the relations indicates that our simulations rule out the scenario in which overmassive BHs evolve onto the relations through gas-rich mergers. By implication our simulations thus disfavor the picture in which supermassive BHs develop significantly before their parent bulges.

There is a growing body of evidence for the presence of multiple stellar populations in some globular clusters, including NGC 1851. For most of these peculiar globular clusters, however, the evidence for the multiple red giant branches (RGBs) having different heavy elemental abundances as observed in ω Centauri is hitherto lacking, although spreads in some lighter elements are reported. It is therefore not clear whether they also share the suggested dwarf galaxy origin of ω Cen or not. Here we show from the CTIO 4 m UVI photometry of the globular cluster NGC 1851 that its RGB is clearly split into two in the U − I color. The two distinct RGB populations are also clearly separated in the abundance of heavy elements as traced by calcium, suggesting that the Type II supernovae enrichment is also responsible, in addition to the pollutions of lighter elements by intermediate-mass asymptotic giant branch stars or fast-rotating massive stars. The RGB split, however, is not shown in the V − I color, as indicated by previous observations. Our stellar population models show that this and the presence of bimodal horizontal-branch distribution in NGC 1851 can be naturally reproduced if the metal-rich second generation stars are also enhanced in helium.