Table of contents

We describe a new method to identify young, late-type stars within ∼150 pc of the Earth that employs visual or near-infrared (NIR) data and the GALEX GR4/5 database. For spectral types later than K5, we demonstrate that the ratio of GALEX near-ultraviolet to visual and NIR emission is larger for stars with ages between 10 and 100 Myr than for older, main-sequence stars. A search in regions of the sky encompassing the TW Hya and Scorpius–Centaurus Associations has returned 54 high-quality candidates for follow up. Spectroscopic observations of 24 of these M1–M5 objects reveal Li 6708 Å absorption in at least 17 systems. Because GALEX surveys have covered a significant fraction of the sky, this methodology should prove valuable for future young star studies.

Two distinct scenarios for the origin of the ∼4 × 10⁸ M_☉ of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae (SNe) could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass asymptotic giant branch (AGB) stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios and observational consequences that can discriminate between the two. We show that AGB stars can produce the inferred mass of dust in this object, however, the final mass of surviving dust depends on the galaxy's star formation history (SFH). In general, SNe cannot produce the observed amount of dust unless the average SN event creates over ∼2 M_☉ of dust in its ejecta. However, special SFHs can be constructed in which SNe can produce the inferred dust mass with a reasonable average dust yield of ∼0.15 M_☉. The two scenarios propose different origins for the galaxy's spectral energy distribution, different star formation efficiencies and stellar masses, and consequently different comoving number densities of J1148+5251-type hyperluminous infrared (IR) objects. The detection of diagnostic mid-IR fine structure lines and more complete surveys determining the comoving number density of these objects can discriminate between the two scenarios.

We analyze the masses and spatial distributions of 14 young stellar groups in Taurus, Lupus3, ChaI, and IC348. These nearby groups, which typically contain 20–40 members, have membership catalogs complete to ∼0.02 M_☉, and are sufficiently young that their locations should be similar to where they formed. These groups show five properties seen in clusters having many more stars and much greater surface density of stars: (1) a broad range of masses, (2) a concentration of the most massive star toward the center of the group, (3) an association of the most massive star with a high surface density of lower mass stars, (4) a correlation of the mass of the most massive star with the total mass of the group, and (5) the distribution of a large fraction of the mass in a small fraction of the stars.

We explore the transmission spectrum of the Neptune-class exoplanet GJ 436b, including the possibility that its atmospheric opacity is dominated by a variety of nonequilibrium chemical products. We also validate our transmission code by demonstrating close agreement with analytic models that use only Rayleigh scattering or water vapor opacity. We find broad disagreement with radius variations predicted by another published model. For GJ 436b, the relative coolness of the planet's atmosphere, along with its implied high metallicity, may make it dissimilar in character compared to "hot Jupiters." Some recent observational and modeling efforts suggest low relative abundances of H₂O and CH₄ present in GJ 436b's atmosphere, compared to calculations from equilibrium chemistry. We include these characteristics in our models and examine the effects of absorption from methane-derived higher-order hydrocarbons. To our knowledge, the effects of these nonequilibrium chemical products on the spectra of close-in giant planets have not previously been investigated. Significant absorption from HCN and C₂H₂ is found throughout the infrared, while C₂H₄ and C₂H₆ are less easily seen. We perform detailed simulations of James Webb Space Telescope observations, including all likely noise sources, and find that we will be able to constrain chemical abundance regimes from this planet's transmission spectrum. For instance, the width of the features at 1.5, 3.3, and 7 μm indicates the amount of HCN versus C₂H₂ present. The NIRSpec prism mode will be useful due to its large spectral range and the relatively large number of photo-electrons recorded per spectral resolution element. However, extremely bright host stars like GJ 436 may be better observed with a higher spectroscopic resolution mode in order to avoid detector saturation. We find that observations with the MIRI low-resolution spectrograph should also have high signal-to-noise in the 5–10 μm range due to the brightness of the star and the relatively low spectral resolution (R ∼ 100) of this mode.

Analysis of an extensive air shower (EAS) detected by surface arrays highly depends on the determination of core locations. Here we present a new method to find the core location of an EAS that, unlike the common methods, does not depend on the lateral distribution function and uses arrival times of secondary particles. This method improves the accuracy of finding the core location of a low-energy EAS in the internal parts of an array, in comparison with common methods.

Radiative transfer and radiation hydrodynamics use the relativistic Boltzmann equation to describe the kinetics of photons. It is difficult to solve the six-dimensional time-dependent transfer equation unless the problem is highly symmetric or in equilibrium. When the radiation field is smooth, it is natural to take angular moments of the transfer equation to reduce the degrees of freedom. However, low order moment equations contain terms that depend on higher order moments. To close the system of moment equations, approximations are made to truncate this hierarchy. Popular closures used in astrophysics include flux-limited diffusion and the M₁ closure, which are rather ad hoc and do not necessarily capture the correct physics. In this paper, we propose a new class of closures for radiative transfer and radiation hydrodynamics. We start from a different perspective and highlight the consistency of a fully relativistic formalism. We present a generic framework to approximate radiative transfer based on relativistic Grad's moment method. We then derive a 14-field method that minimizes unphysical photon self-interaction.

We present the first results from the inversion of full acoustic wavefield in the helioseismic context. In contrast to time–distance helioseismology, which involves analyzing the travel times of seismic waves propagating into the solar interior, wavefield tomography models both the travel times and amplitude variations present in the entire seismic record. Unlike the use of ray-based, Fresnel-zone, Born, or Rytov approximations in previous time–distance studies, this method does not require any simplifications to be made to the sensitivity kernel in the inversion. In this study, the acoustic wavefield is simulated for all iterations in the inversion. The sensitivity kernel is therefore updated while lateral variations in sound-speed structure in the model emerge during the course of the inversion. Our results demonstrate that the amplitude-based inversion approach is capable of resolving sound-speed structures defined by relatively sharp vertical and horizontal boundaries. This study therefore provides the foundation for a new type of subsurface imaging in local helioseismology that is based on the inversion of the entire seismic wavefield.

Observations with the adaptive optics system on the Very Large Telescope reveal that the outer main belt asteroid (702) Alauda has a small satellite with primary to secondary diameter ratio of ∼56. The secondary revolves around the primary in 4.9143 ± 0.007 days at a distance of 1227 ± 24 km, yielding a total system mass of (6.057 ± 0.36) × 10¹⁸ kg. Combined with an IRAS size measurement, our data yield a bulk density of 1570 ± 500 kg m⁻³ for this B-type asteroid.

The electron–cyclotron maser (ECM) conventionally driven by velocity anisotropies of energetic electrons trapped in magnetic fields is one of the most important radio-emission mechanisms in astrophysics. Recently, Wu and Tang proposed that a proper lower energy cutoff behavior of power-law electrons can effectively excite the ECM emission. This paper considers effects of temperature anisotropy on this new ECM mechanism. The results show that the growth rates of the ECM emissions increase with β_⊥0 and β_∥0, where β_⊥0 and β_∥0 are the perpendicular and parallel velocity spreads (in units of the light velocity c) of the energetic electron beam, respectively. Moreover, the growth rates of O1 and X2 modes both sensitively depend on the ratio of the electron–cyclotron frequency to the plasma frequency Ω and reach their extremum values at Ω ≃ 1.5 for the O1 mode and at Ω ≃ 1.0 for the X2 mode. Meanwhile, as the mean velocity of the electron beam β_s (in units of c) increases, the growth rate of the O1 mode remains approximately constant and that of the X2 mode decreases considerably.

Previous ground-based observations of the Seyfert 2 galaxy Mrk 78 revealed a double set of emission lines, similar to those seen in several active galactic nuclei (AGNs) from recent surveys. Are the double lines due to two AGNs with different radial velocities in the same galaxy, or are they due to mass outflows from a single AGN? We present a study of the outflowing ionized gas in the resolved narrow-line region (NLR) of Mrk 78 using observations from the Space Telescope Imaging Spectrograph (STIS) and Faint Object Camera aboard the Hubble Space Telescope as part of an ongoing project to determine the kinematics and geometries of AGN outflows. From the spectroscopic information, we determined the fundamental geometry of the outflow via our kinematics modeling program by recreating radial velocities to fit those seen in four different STIS slit positions. We determined that the double emission lines seen in ground-based spectra are due to an asymmetric distribution of outflowing gas in the NLR. By successfully fitting a model for a single AGN to Mrk 78, we show that it is possible to explain double emission lines with radial velocity offsets seen in AGN similar to Mrk 78 without requiring dual supermassive black holes.

We present a light-curve model of the symbiotic nova PU Vul (Nova Vulpeculae 1979) that shows a long-lasting flat peak with no spectral indication of wind mass loss before decline. Our quasi-evolution models consisting of a series of static solutions explain both the optical flat peak and ultraviolet (UV) light curve simultaneously. The white dwarf mass is estimated to be ∼0.6 M_☉. We also provide a new determination of the reddening, E(B − V) = 0.43 ± 0.05, from UV spectral analysis. Theoretical light-curve fitting of UV 1455 Å provides the distance of d = 3.8 ± 0.7 kpc.

We present a composite spectrum of 60 long duration gamma-ray burst (GRB) afterglows with redshifts in the range 0.35 < z < 6.7 observed with low-resolution optical spectra. The composite spectrum covers the wavelength range 700–6600 Å in the rest frame and has a mean signal-to-noise ratio of 150 per 1 Å pixel and reaches a maximum of ∼300 in the range 2500–3500 Å. Equivalent widths are measured from metal absorption lines from the Lyα line to ∼5200 Å, and associated metal and hydrogen lines are identified between the Lyman break and Lyα line. The average transmission within the Lyman forest is consistent with that found along quasar lines of sight. We find a temporal variation in fine-structure lines when dividing the sample into bursts observed within 2 hr from their trigger and those observed later. Other lines in the predominantly neutral gas show variations too, but this is most likely a random effect caused by weighting of individual strong absorption lines and which mimics a temporal variation. Bursts characterized with high- or low-prompt GRB energy release produce afterglows with similar absorption line strengths, and likewise for bursts with bright or faint optical afterglows. Bursts defined as dark from their optical to X-ray spectral index have stronger absorption lines relative to the optically bright bursts. The composite spectrum has strong Ca ii and Mg ii absorption lines as commonly found in dusty galaxies, however, we find no evidence for dust or a significant molecular content based on the non-detection of diffuse interstellar bands. Compared to starburst galaxy spectra, the GRB composite has much stronger fine-structure lines, while metal absorption lines are weaker.

Both ground- and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. The variation in a planet's transit times may be used to infer the presence of additional planets. Deducing the masses and orbital parameters of such planets from transit time variations (TTVs) alone is a rich and increasingly relevant dynamical problem. In this work, we evaluate the extent of the degeneracies in this process, systematically explore the dependence of TTV signals on several parameters, and provide phase space plots that could aid observers in planning future observations. Our explorations are focused on a likely-to-be prevalent situation: a known transiting short-period Neptune- or Jupiter-sized planet and a suspected external low-mass perturber on a nearly coplanar orbit. Through ∼10⁷N-body simulations, we demonstrate how TTV signal amplitudes may vary by orders of magnitude due to slight variations in any one orbital parameter (10⁻³ AU in a semimajor axis, 0.005 in eccentricity, or a few degrees in orbital angles), and quantify the number of consecutive transit observations necessary in order to obtain a reasonable opportunity of characterizing the unseen planet (≳50 observations). Planets in or near period commensurabilities of the form p:q, where p ⩽ 20 and q ⩽ 3, produce distinct TTV signatures, regardless of whether the planets are actually locked in a mean motion resonance. We distinguish these systems from the secular systems in our explorations. Additionally, we find that computing the autocorrelation function of a TTV signal can provide a useful diagnostic for identifying possible orbits for additional planets and suggest that this method could aid integration of TTV signals in future studies of particular exosystems.

The radii of some transiting extrasolar giant planets are larger than would be expected by the standard theory. We address this puzzle with the model of coupled radius–orbit tidal evolution developed by Ibgui & Burrows. The planetary radius is evolved self-consistently with orbital parameters, under the influence of tidal torques and tidal dissipation in the interior of the planet. A general feature of this model, which we have previously demonstrated in the generic case, is that a possible transient inflation of the planetary radius can temporarily interrupt its standard monotonic shrinking and can lead to the inflated radii that we observe. Importantly, we demonstrate that the use of a constant time lag model for the orbital evolution does not improve the accuracy of the evolutionary calculations. First, though formulated in a closed form by the equations of Hut, it is not valid at large eccentricities, as for the constant phase lag model truncated at the second order in eccentricity that we adopt; ambiguities in tidal theories are perhaps the most significant source of uncertainty in evolutionary calculations. Second, we find evolutionary tracks that fit within the 1σ error bars, the radius, the eccentricity, and the semimajor axis of HD 209458b in its current estimated age range, using the constant time lag model, as we find fitting tracks with the constant phase lag model. Both models show that a bloated planet with a circular orbit may still be inflated, due to thermal inertia. We have modified our constant phase lag model to include an orbital period dependence of the tidal dissipation factor in the star, Q'_* ∝ P^γ, −1 ⩽ γ ⩽ 1. For some inflated planets (WASP-6b and WASP-15b), we find fitting tracks; for another (TrES-4), we do not; and for others (WASP-4b and WASP-12b), we find fitting tracks, but our model might imply that we are observing the planets at a special time. Finally, we stress a 2–3 order-of-magnitude timescale uncertainty of the inspiraling phase of the planet into its host star, arising from uncertainties in Q'_*.

We study the impact of dust evolution in a protoplanetary disk (PPD) around a T Tauri star on the disk's chemical composition. For the first time, we utilize a comprehensive model of dust evolution, which includes growth, fragmentation, and sedimentation. Specific attention is paid to the influence of grain evolution on the penetration of the UV field in the disk. A chemical model that includes a comprehensive set of gas-phase and grain-surface chemical reactions is used to simulate the chemical structure of the disk. The main effect of grain evolution on the disk's chemical composition comes from sedimentation and, to a lesser degree, from reduction of the total grain-surface area. The net effect of grain growth is suppressed by the fragmentation process which maintains a population of small grains, dominating the total grain surface area. We consider three models of dust properties. In model GS, both growth and sedimentation are taken into account. In models A5 and A4, all grains are assumed to be the same size (10⁻⁵ cm and 10⁻⁴ cm, respectively) with a constant gas-to-dust mass ratio of 100. As in previous studies, the "three-layer" pattern (cold midplane, warm molecular layer, and hot atmosphere) in the disk-chemical structure is preserved in all models, but shifted closer to the midplane in models with increased grain size (GS and A4). Unlike other similar studies, we find that in models GS and A4, the column densities of most gas-phase species are enhanced by 1–3 orders of magnitude relative to those in a model with pristine dust (A5), while column densities of their surface counterparts are decreased. We show that column densities of certain species, such as C₂H, HC_2n+1N (n = 0–3), H₂O, and some other molecules, as well as the C₂H₂/HCN abundance ratio, all of which are accessible with Herschel and ALMA, can be used as observational tracers of early stages of the grain evolution process in PPDs.

Favored theories of giant planet formation center around two main paradigms, namely the core accretion model and the gravitational instability model. These two formation scenarios support the hypothesis that the giant planet metallicities should be higher or equal to that of the parent star. Meanwhile, spectra of the transiting hot Jupiter HD189733b suggest that carbon and oxygen abundances range from depleted to enriched with respect to the star. Here, using a model describing the formation sequence and composition of planetesimals in the protoplanetary disk, we determine the range of volatile abundances in the envelope of HD189733b that is consistent with the 20–80 M_⊕ of heavy elements estimated to be present in the planet's envelope. We then compare the inferred carbon and oxygen abundances to those retrieved from spectroscopy, and we find a range of supersolar values that directly fit both spectra and internal structure models. In some cases, we find that the apparent contradiction between the subsolar elemental abundances and the mass of heavy elements predicted in HD189733b by internal structure models can be explained by the presence of large amounts of carbon molecules in the form of polycyclic aromatic hydrocarbons and soots in the upper layers of the envelope, as suggested by recent photochemical models. A diagnostic test that would confirm the presence of these compounds in the envelope is the detection of acetylene. Several alternative hypotheses that could also explain the subsolar metallicity of HD189733b are formulated: the possibility of differential settling in its envelope, the presence of a larger core that did not erode with time, a mass of heavy elements lower than the one predicted by interior models, a heavy element budget resulting from the accretion of volatile-poor planetesimals in specific circumstances, or the combination of all these mechanisms.

We present metallicity distribution functions (MDFs) for the central regions of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II, Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the published catalog of abundance measurements from the previous paper in this series. The measurements are based on spectral synthesis of iron absorption lines. For each MDF, we determine maximum likelihood fits for Leaky Box, Pre-Enriched, and Extra Gas (wherein the gas supply available for star formation increases before it decreases to zero) analytic models of chemical evolution. Although the models are too simplistic to describe any MDF in detail, a Leaky Box starting from zero metallicity gas fits none of the galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly the more luminous ones, strongly prefer the Extra Gas Model to the other models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly better than the Extra Gas Model. The best-fit effective yields of the less luminous half of our galaxy sample do not exceed 0.02 Z_☉, indicating that gas outflow is important in the chemical evolution of the less luminous galaxies. We surmise that the ratio of the importance of gas infall to gas outflow increases with galaxy luminosity. Strong correlations of average [Fe/H] and metallicity spread with luminosity support this hypothesis.

We derive the star formation histories of eight dwarf spheroidal (dSph) Milky Way satellite galaxies from their alpha element abundance patterns. Nearly 3000 stars from our previously published catalog comprise our data set. The average [α/Fe] ratios for all dSphs follow roughly the same path with increasing [Fe/H]. We do not observe the predicted knees in the [α/Fe] versus [Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae begin to explode. Instead, we find that Type Ia supernova ejecta contribute to the abundances of all but the most metal-poor ([Fe/H] < −2.5) stars. We have also developed a chemical evolution model that tracks the star formation rate, Types II and Ia supernova explosions, and supernova feedback. Without metal enhancement in the supernova blowout, massive amounts of gas loss define the history of all dSphs except Fornax, the most luminous in our sample. All six of the best-fit model parameters correlate with dSph luminosity but not with velocity dispersion, half-light radius, or Galactocentric distance.

Strong gravitational lensing of an extended object is described by a mapping from source to image coordinates that is nonlinear and cannot generally be inverted analytically. Determining the structure of the source intensity distribution also requires a description of the blurring effect due to a point-spread function. This initial study uses an iterative gravitational lens modeling scheme based on the semilinear method to determine the linear parameters (source intensity profile) of a strongly lensed system. Our "matrix-free" approach avoids construction of the lens and blurring operators while retaining the least-squares formulation of the problem. The parameters of an analytical lens model are found through nonlinear optimization by an advanced genetic algorithm (GA) and particle swarm optimizer (PSO). These global optimization routines are designed to explore the parameter space thoroughly, mapping model degeneracies in detail. We develop a novel method that determines the L-curve for each solution automatically, which represents the trade-off between the image χ² and regularization effects, and allows an estimate of the optimally regularized solution for each lens parameter set. In the final step of the optimization procedure, the lens model with the lowest χ² is used while the global optimizer solves for the source intensity distribution directly. This allows us to accurately determine the number of degrees of freedom in the problem to facilitate comparison between lens models and enforce positivity on the source profile. In practice, we find that the GA conducts a more thorough search of the parameter space than the PSO.

We have performed submillimeter and millimeter observations in CO lines toward supernova remnant (SNR) IC443. The CO molecular shell coincides well with the partial shell of the SNR detected in radio continuum observations. Broad emission lines and three 1720 MHz OH masers were detected in the CO molecular shell. The present observations have provided further evidence in support of the interaction between the SNR and the adjoining molecular clouds (MCs). The total mass of the MCs is 9.26 × 10³ M_☉. The integrated CO line intensity ratio $(R_{I_{\rm CO(3-2)}/I_{\rm CO(2-1)}})$ for the whole MC is between 0.79 and 3.40. The average value is 1.58, which is much higher than previous measurements of individual Galactic MCs. Higher line ratios imply that shocks have driven into the MCs. We conclude that high $R_{I_{\rm CO(3-2)}/I_{\rm CO(2-1)}}$ is identified as a good signature of the SNR–MC interacting system. Based on the IRAS Point Source Catalog and the Two Micron All Sky Survey near-infrared database, 12 protostellar object and 1666 young stellar object (YSO) candidates (including 154 classical T Tauri stars and 419 Herbig Ae/Be stars) are selected. In the interacting regions, the significant enhancement of the number of protostellar objects and YSOs indicates the presence of some recently formed stars. After comparing the characteristic timescales of star formation with the age of IC443, we conclude that the protostellar objects and YSO candidates are not triggered by IC443. For the age of the stellar winds shell, we have performed our calculation on the basis of a stellar wind shell expansion model. The results and analysis suggest that the formation of these stars may be triggered by the stellar winds of the IC443 progenitor.

The Suzaku observation of a giant radio galaxy 3C 35 revealed faint extended X-ray emission, associated with its radio lobes and/or host galaxy. After careful subtraction of the X-ray and non-X-ray background and contaminating X-ray sources, the X-ray spectrum of the faint emission was reproduced by a sum of the power-law (PL) and soft thermal components. The soft component was attributed to the thermal plasma emission from the host galaxy. The photon index of the PL component, Γ = 1.35^+0.56_−0.86^+0.11_−0.10, where the first and second errors represent the statistical and systematic ones, was found to agree with the synchrotron radio index from the lobes, Γ_R = 1.7. Thus, the PL component was attributed to the inverse Compton (IC) X-rays from the synchrotron electrons in the lobes. The X-ray flux density at 1 keV was derived as 13.6 ± 5.4^+4.0_−3.6 nJy with the photon index fixed at the radio value. The X-ray surface brightness from these lobes (∼0.2 nJy arcmin⁻²) is lowest among the lobes studied through the IC X-ray emission. In combination with the synchrotron radio flux density, 7.5 ± 0.2 Jy at 327.4 MHz, the electron energy density spatially averaged over the lobes was evaluated to be the lowest among those radio galaxies, as u_e = (5.8 ± 2.3^+1.9_−1.7) × 10⁻¹⁴ erg cm⁻³ over the electron Lorentz factor of 10³–10⁵. The magnetic energy density was calculated as u_m = (3.1^+2.5_−1.0^+1.4_−0.9) × 10⁻¹⁴ erg cm⁻³, corresponding to the magnetic field strength of 0.88^+0.31_−0.16^+0.19_−0.14 μG. These results suggest that the energetics in the 3C 35 lobes are nearly consistent with equipartition between the electrons and magnetic fields.

We carry out a multi-wavelength study of individual galaxies detected by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) and identified at other wavelengths, using data spanning the radio to the ultraviolet (UV). We develop a Monte Carlo method to account for flux boosting, source blending, and correlations among bands, which we use to derive deboosted far-infrared (FIR) luminosities for our sample. We estimate total star-formation rates (SFRs) for BLAST counterparts with z ⩽ 0.9 by combining their FIR and UV luminosities. Star formation is heavily obscured at L_FIR ≳ 10¹¹ L_☉, z ≳ 0.5, but the contribution from unobscured starlight cannot be neglected at L_FIR ≲ 10¹¹ L_☉, z ≲ 0.25. We assess that about 20% of the galaxies in our sample show indication of a type 1 active galactic nucleus, but their submillimeter emission is mainly due to star formation in the host galaxy. We compute stellar masses for a subset of 92 BLAST counterparts; these are relatively massive objects, with a median mass of ∼10¹¹ M_☉, which seem to link the 24 μm and Submillimetre Common-User Bolometer Array (SCUBA) populations, in terms of both stellar mass and star formation activity. The bulk of the BLAST counterparts at z ≲ 1 appears to be run-of-the-mill star-forming galaxies, typically spiral in shape, with intermediate stellar masses and practically constant specific SFRs. On the other hand, the high-z tail of the BLAST counterparts significantly overlaps with the SCUBA population, in terms of both SFRs and stellar masses, with observed trends of specific SFR that support strong evolution and downsizing.

We have developed an axisymmetric steady-state solar wind model that describes properties of the large-scale solar wind, interplanetary magnetic field, and turbulence throughout the heliosphere from 0.3 AU to 100 AU. The model is based on numerical solutions of large-scale Reynolds-averaged magnetohydrodynamic equations coupled with a set of small-scale transport equations for the turbulence energy, normalized cross helicity, and correlation scale. The combined set of time-dependent equations is solved in the frame of reference corotating with the Sun using a time-relaxation method. We use the model to study the self-consistent interaction between the large-scale solar wind and smaller-scale turbulence and the role of the turbulence in the large-scale structure and temperature distribution in the solar wind. To illuminate the roles of the turbulent cascade and the pickup protons in heating the solar wind depending on the heliocentric distance, we compare the model results with and without turbulence/pickup protons. The variations of plasma temperature in the outer heliosphere are compared with Ulysses and Voyager 2 observations.

We present arcsecond-scale Submillimeter Array observations of the CO(3–2) line emission from the disks around the young stars HD 163296 and TW Hya at a spectral resolution of 44 m s⁻¹. These observations probe below the ∼100 m s⁻¹ turbulent linewidth inferred from lower-resolution observations, and allow us to place constraints on the turbulent linewidth in the disk atmospheres. We reproduce the observed CO(3–2) emission using two physical models of disk structure: (1) a power-law temperature distribution with a tapered density distribution following a simple functional form for an evolving accretion disk, and (2) the radiative transfer models developed by D'Alessio et al. that can reproduce the dust emission probed by the spectral energy distribution. Both types of models yield a low upper limit on the turbulent linewidth (Doppler b-parameter) in the TW Hya system (≲40 m s⁻¹) and a tentative (3σ) detection of a ∼300 m s⁻¹ turbulent linewidth in the upper layers of the HD 163296 disk. These correspond to roughly ⩽10% and 40% of the sound speed at size scales commensurate with the resolution of the data. The derived linewidths imply a turbulent viscosity coefficient, α, of order 0.01 and provide observational support for theoretical predictions of subsonic turbulence in protoplanetary accretion disks.

The issue of giant planet formation by core accretion (CA) far from the central star is rather controversial because the growth of a massive solid core necessary for triggering the gas runaway can take longer than the lifetime of the protoplanetary disk. In this work, we assess the range of separations at which CA may operate by (1) allowing for an arbitrary (physically meaningful) rate of planetesimal accretion by the core and (2) properly taking into account the dependence of the critical mass for the gas runaway on the planetesimal accretion luminosity. This self-consistent approach distinguishes our work from similar studies in which only a specific planetesimal accretion regime was explored and/or the critical core mass was fixed at some arbitrary level. We demonstrate that the largest separation at which the gas runaway can occur within 3 Myr corresponds to the surface density of solids in the disk ≳0.1 g cm⁻² and is 40–50 AU in the minimum mass solar nebula. This limiting separation is achieved when the planetesimal accretion proceeds at the fastest possible rate, even though the high associated accretion luminosity increases the critical core mass, delaying the onset of gas runaway. Our constraints are independent of the mass of the central star and vary only weakly with the core density and its atmospheric opacity. We also discuss various factors that can strengthen or weaken our limits on the operation of CA.

We study a class of early dark energy (EDE) models, in which, unlike in standard dark energy models, a substantial amount of dark energy exists in the matter-dominated era. We self-consistently include dark energy perturbations, and show that these models may be successfully constrained using future observations of galaxy clusters, in particular the redshift abundance, and the Sunyaev–Zel'dovich (SZ) power spectrum. We make predictions for EDE models, as well as ΛCDM for incoming X-ray (eROSITA) and microwave (South Pole Telescope) observations. We show that galaxy clusters' mass function and the SZ power spectrum will put strong constraints both on the equation of state of dark energy today and the redshift at which EDE transits to present-day ΛCDM-like behavior for these models, thus providing complementary information to the geometric probes of dark energy. Not including perturbations in EDE models leads to those models being practically indistinguishable from ΛCDM. An MCMC analysis of future galaxy cluster surveys provides constraints for EDE parameters that are competitive with and complementary to background expansion observations such as supernovae.

We use UBVI  Hα images of the Whirlpool galaxy, M51, taken with the Advanced Camera for Surveys and WFPC2 cameras on the Hubble Space Telescope (HST) to select star clusters, and to estimate their masses and ages by comparing their observed colors with predictions from population synthesis models. We construct the mass function of intermediate-age (1–4 × 10⁸ yr) clusters, and find that it is well described by a power law, ψ(M) ∝ M^β, with β = −2.1 ± 0.2, for clusters more massive than M ≈ 6 × 10³ M_☉. This extends the mass function of intermediate-age clusters in M51 to masses lower by nearly a factor of five over previous determinations. The mass function does not show evidence for curvature at either the high or low mass end. This shape indicates that there is no evidence for the earlier disruption of lower mass clusters compared with their higher mass counterparts (i.e., no mass-dependent disruption) over the observed range of masses and ages, or for a physical upper mass limit M_C with which clusters in M51 can form. These conclusions differ from previous suggestions based on poorer-quality HST observations. We discuss their implications for the formation and disruption of the clusters. Ages of clusters in two "feathers," stellar features extending from the outer portion of a spiral arm, show that the feather with a larger pitch angle formed earlier, and over a longer period, than the other.

Depending on mass and metallicity as well as evolutionary phase, stars occasionally experience convective–reactive nucleosynthesis episodes. We specifically investigate the situation when nucleosynthetically unprocessed, H-rich material is convectively mixed with an He-burning zone, for example in a convectively unstable shell on top of electron-degenerate cores in asymptotic giant branch stars, young white dwarfs, or X-ray bursting neutron stars. Such episodes are frequently encountered in stellar evolution models of stars of extremely low or zero metal content, such as the first stars. We have carried out detailed nucleosynthesis simulations based on stellar evolution models and informed by hydrodynamic simulations. We focus on the convective–reactive episode in the very late thermal pulse star Sakurai's object (V4334 Sagittarii). Asplund et al. determined the abundances of 28 elements, many of which are highly non-solar, ranging from H, He, and Li all the way to Ba and La, plus the C isotopic ratio. Our simulations show that the mixing evolution according to standard, one-dimensional stellar evolution models implies neutron densities in the He intershell (≲ few 10¹¹ cm⁻³) that are too low to obtain a significant neutron capture nucleosynthesis on the heavy elements. We have carried out three-dimensional hydrodynamic He-shell flash convection simulations in 4π geometry to study the entrainment of H-rich material. Guided by these simulations we assume that the ingestion process of H into the He-shell convection zone leads only after some delay time to a sufficient entropy barrier that splits the convection zone into the original one driven by He burning and a new one driven by the rapid burning of ingested H. By making such mixing assumptions that are motivated by our hydrodynamic simulations we obtain significantly higher neutron densities (∼ few 10¹⁵ cm⁻³) and reproduce the key observed abundance trends found in Sakurai's object. These include an overproduction of Rb, Sr, and Y by about two orders of magnitude higher than the overproduction of Ba and La. Such a peculiar nucleosynthesis signature is impossible to obtain with the mixing predictions in our one-dimensional stellar evolution models. The simulated Li abundance and the isotopic ratio ¹²C/¹³C are as well in agreement with observations. Details of the observed heavy element abundances can be used as a sensitive diagnostic tool for the neutron density, for the neutron exposure and, in general, for the physics of the convective–reactive phases in stellar evolution. For example, the high elemental ratio Sc/Ca and the high Sc production indicate high neutron densities. The diagnostic value of such abundance markers depends on uncertain nuclear physics input. We determine how our results depend on uncertainties of nuclear reaction rates, for example for the ¹³C(α, n)¹⁶O reaction.

We present spatially resolved scattered light images of the circumstellar disk around HK Tau B at 3.8 and 4.7 μm taken with the Keck Telescope Laser Guide Star Adaptive Optics (AO) system, and 1.6–2.12 μm images taken with the Very Large Telescope/NACO AO system. Combined with previously published optical Hubble Space Telescope data, we investigate the spatially resolved scattered light properties of this edge-on circumstellar disk and probe for the presence of large grains. The 0.6–3.8 μm scattered light observations reveal strong, and in some cases, unusual, wavelength dependencies in the observed disk morphology. The separation between the two scattered light nebulae, which is directly proportional to the disk-mass–opacity product, decreases by 30% between 0.6 and 3.8 μm. Over the same wavelength range, the FWHM of the disk nebulosity declines by a factor of two, while the flux ratio between the two nebulae increases by a factor of ∼8. No other disk known to date shows a flux ratio that increases with wavelength. Both the FWHM and nebula flux ratio are affected by the scattering phase function and the observed behavior can most readily be explained by a phase function that becomes more forward throwing with wavelength. The multi-wavelength scattered light observations also confirm the asymmetric nature of the disk and show that the level of asymmetry is a function of wavelength. We use the MCFOST radiative transfer code to model the disk at four wavelengths, corresponding to the I, H, Ks, and L' bandpasses. A single power-law grain size distribution can recreate the observed disk properties simultaneously at all four wavelengths. Bayesian analysis of the dust parameters finds a 99% probability that the maximum grain size is 5.5 μm or larger. We also find that the grain size distribution is steep, with a 99% probability of a power-law index of 4.2 or larger, suggesting that these large grains are a small fraction of the overall dust population. The best-fit dust asymmetry parameter for each individual wavelength shows an unusual behavior, increasing with wavelength from the optical through the near-infrared, peaking at ∼0.8 between 2.2 and 3.8 μm, then decreasing by a factor of two by ∼12 μm. Comparing the wavelength dependence of the asymmetry parameter for HK Tau B with those for the interstellar medium (ISM) and dark cloud dust models, we find considerable evolution from an ISM state and argue for the presence of grain growth within the disk. Further, comparing the wavelength dependence of the asymmetry parameter for GG Tau, HV Tau C, and HK Tau B, the three disks that have been spatially resolved in scattered light between 0.8 and 3.8 μm, finds a diverse range of dust properties, indicating differing degrees of grain growth for disks at a similar age.

Ammonia is a major reservoir of nitrogen atoms in cometary materials. However, detections of ammonia in comets are rare, with several achieved at radio wavelengths. A few more detections were obtained through near-infrared observations (around the 3 μm wavelength region), but moderate relative velocity shifts are required to separate emission lines of cometary ammonia from telluric absorption lines in the 3 μm wavelength region. On the other hand, the amidogen radical (NH₂—a photodissociation product of ammonia in the coma) also shows rovibrational emission lines in the 3 μm wavelength region. Thus, gas production rates for ammonia can be determined from the rovibrational emission lines of ammonia (directly) and amidogen radical (indirectly) simultaneously in the near-infrared. In this article, we present new fluorescence excitation models for cometary ammonia and amidogen radical in the near-infrared, and we apply these models to the near-infrared high-dispersion spectra of comet C/2004 Q2 (Machholz) to determine the mixing ratio of ammonia to water in the comet. Based on direct detection of NH₃ lines, the mixing ratio of NH₃/H₂O is 0.46% ± 0.03% in C/2004 Q2 (Machholz), in agreement with other results. The mixing ratio of ammonia determined from the NH₂ observations (0.31%–0.79%) is consistent but has relatively larger error, owing to uncertainty in the photodissociation rates of ammonia. At the present level of accuracy, we confirm that NH₃ could be the sole parent of NH₂ in this comet.

Lyne & Manchester identified a group of some 50 pulsars they called "partial cones" which they found difficult to classify and interpret. They were notable for their asymmetric average profiles and asymmetric polarization position angle (PPA) traverses, wherein the steepest gradient (SG) point fell toward one edge of the total intensity profile. Over the last two decades, this population of pulsars has raised cautions regarding the core/cone model of the radio pulsar emission beam which implies a high degree of order, symmetry, and geometric regularity. In this paper, we reinvestigate this population "partial cone" pulsars on the basis of new single pulse polarimetric observations of 39 of them, observed with the Giant Meterwave Radio Telescope in India and the Arecibo Observatory in Puerto Rico. These highly sensitive observations help us to establish that most of these "partial cones" exhibit a core/cone structure just as did the "normal" pulsars studied in the earlier papers of this series. In short, we find that many of these "partial cones" are partial in the sense that the emission above different areas of their polar caps can be (highly) asymmetric. However, when studied closely we find that their emission geometries are overall identical to a core/double cone structure encountered earlier—that is, with specific conal dimensions scaling as the polar cap size. Further, the "partial cone" population includes a number of stars with conal single profiles that are asymmetric at meter wavelengths for unknown reasons (e.g., like those of B0809+74 or B0943+10). We find that aberration–retardation appears to play a role in distorting the core/cone emission-beam structure in rapidly rotating pulsars. We also find several additional examples of highly polarized pre- and postcursor features that do not appear to be generated at low altitude but rather at high altitude, far from the usual polar flux tube emission sites of the core and conal radiation.

Prior imaging of the lenticular galaxy, NGC 3998, with the Hubble Space Telescope revealed a small, highly inclined, nuclear ionized gas disk, the kinematics of which indicate the presence of a 270 million solar mass black hole. Plausible kinematic models are used to constrain the size of the broad emission line region (BELR) in NGC 3998 by modeling the shape of the broad Hα, Hβ, and Hγ emission line profiles. The analysis indicates that the BELR is large with an outer radius ∼7 pc, regardless of whether the kinematic model is represented by an accretion disk or a spherically symmetric inflow. The electron temperature in the BELR is ⩽ 28,800 K consistent with photoionization by the active galactic nucleus (AGN). Indeed, the AGN is able to sustain the ionization of the BELR, albeit with a high covering factor ranging between 20% and 100% depending on the spectral energy distribution adopted for the AGN. The high covering factor favors a spherical distribution for the gas as opposed to a thin disk. If the gas density is ⩾7 × 10³ cm⁻³ as indicated by the broad forbidden [S ii] emission line ratio, then interpreting the broad Hα emission line in terms of a steady state spherically symmetric inflow leads to a rate ⩽ 6.5 × 10⁻² M_☉ yr⁻¹ which exceeds the inflow requirement to explain the X-ray luminosity in terms of a radiatively inefficient inflow by a factor of ⩽18.

We present templates for the Sunyaev–Zel'dovich (SZ) angular power spectrum based on four models for the nonlinear gas distribution. The frequency-dependent SZ temperature fluctuations, with thermal (TSZ) and kinetic (KSZ) contributions, are calculated by tracing through a dark matter simulation, processed to include gas in dark matter halos and in the filamentary intergalactic medium. Different halo gas models are compared to study how star formation, energetic feedback, and nonthermal pressure support influence the angular power spectrum. The standard model has been calibrated to reproduce the stellar and gas fractions and X-ray scaling relations measured from low-redshift clusters and groups. The other models illustrate the current theoretical and empirical uncertainties relating to properties of the intracluster medium. Relative to the standard model, their angular power spectra differ by approximately ±50% (TSZ), ±20% (KSZ), and ±40% (SZ at 148 GHz) for l = 3000, σ₈ = 0.8, and homogeneous reionization at z = 10. The angular power spectrum decreases in amplitude as gas mass and binding energy are removed through star formation, and as gas is pushed out to larger radii by energetic feedback. With nonthermal pressure support, less pressure is required to maintain hydrostatic equilibrium, thus reducing the thermal contribution to the SZ power. We also calculate the SZ templates as a function of σ₈ and quantify this dependence. Assuming C_l ∝ (σ₈/0.8)^α, the effective scaling index ranges from 7 ≲ α_TSZ ≲ 9, 4.5 ≲ α_KSZ ≲ 5.5, and 6.5 ≲ α_SZ(148 GHz) ≲ 8 at l = 3000 for 0.6 < σ₈ < 1. The template spectra are publicly available and can be used when fitting for the SZ contribution to the cosmic microwave background on arcminute scales.

The merger of a binary system composed of a black hole (BH) and a neutron star (NS) may leave behind a torus of hot, dense matter orbiting around the BH. While numerical-relativity simulations are necessary to simulate this process accurately, they are also computationally expensive and unable at present to cover the large space of possible parameters, which include the relative mass ratio, the stellar compactness, and the BH spin. To mitigate this and provide a first reasonable coverage of the space of parameters, we have developed a method for estimating the mass of the remnant torus from BH–NS mergers. The toy model makes use of an improved relativistic affine model to describe the tidal deformations of an extended tri-axial ellipsoid orbiting around a Kerr BH and measures the mass of the remnant torus by considering which of the fluid particles composing the star are on bound orbits at the time of the tidal disruption. We tune the toy model by using the results of fully general-relativistic simulations obtaining relative precisions of a few percent and use it to investigate the space of parameters extensively. In this way, we find that the torus mass is largest for systems with highly spinning BHs, small stellar compactnesses, and large mass ratios. As an example, tori as massive as M_b,tor ≃ 1.33 M_☉ can be produced for a very extended star with compactness C ≃ 0.1 inspiralling around a BH with dimensionless spin parameter a = 0.85 and mass ratio q ≃ 0.3. However, for a more astrophysically reasonable mass ratio q ≃ 0.14 and a canonical value of the stellar compactness C ≃ 0.145, the toy model sets a considerably smaller upper limit of M_b,tor ≲ 0.34 M_☉.

We present a joint gravitational lensing and stellar-dynamical analysis of 11 early-type galaxies (median deflector redshift z_d = 0.5) from Strong Lenses in the Legacy Survey (SL2S). Using newly measured redshifts and stellar velocity dispersions from Keck spectroscopy with lens models from Paper I, we derive the total mass-density slope inside the Einstein radius for each of the 11 lenses. The average total density slope is found to be 〈γ'〉 = 2.16^+0.09_−0.09 ($\rho _{\rm tot}\propto r^{-\gamma ^{\prime }}$), with an intrinsic scatter of 0.25^+0.10_−0.07. We also determine the dark matter fraction for each lens within half the effective radius, R_eff/2, and find the average-projected dark matter mass fraction to be 0.42^+0.08_−0.08 with a scatter of 0.20^+0.09_−0.07 for a Salpeter initial mass function. By combining the SL2S results with those from the Sloan Lens ACS Survey (median z_d = 0.2) and the Lenses Structure and Dynamics Survey (median z_d = 0.8), we investigate cosmic evolution of γ' and find a mild trend ∂〈γ'〉/∂z_d = −0.25^+0.10_−0.12. This suggests that the total density profile of massive galaxies has become slightly steeper over cosmic time. If this result is confirmed by larger samples, it would indicate that dissipative processes played some role in the growth of massive galaxies since z ∼ 1.

Radiation pressure from the absorption and scattering of starlight by dust grains may be an important feedback mechanism in regulating star-forming galaxies. We compile data from the literature on star clusters, star-forming subregions, normal star-forming galaxies, and starbursts to assess the importance of radiation pressure on dust as a feedback mechanism, by comparing the luminosity and flux of these systems to their dust Eddington limit. This exercise motivates a novel interpretation of the Schmidt law, the L_IR–L'_CO correlation, and the L_IR–L'_HCN correlation. In particular, the linear L_IR–L'_HCN correlation is a natural prediction of radiation pressure regulated star formation. Overall, we find that the Eddington limit sets a hard upper bound to the luminosity of any star-forming region. Importantly, however, many normal star-forming galaxies have luminosities significantly below the Eddington limit. We explore several explanations for this discrepancy, especially the role of "intermittency" in normal spirals—the tendency for only a small number of subregions within a galaxy to be actively forming stars at any moment because of the time dependence of the feedback process and the luminosity evolution of the stellar population. If radiation pressure regulates star formation in dense gas, then the gas depletion timescale is 6 Myr, in good agreement with observations of the densest starbursts. Finally, we highlight the importance of observational uncertainties, namely, the dust-to-gas ratio and the CO-to-H₂ and HCN-to-H₂ conversion factors, that must be understood before a definitive assessment of radiation pressure as a feedback mechanism in star-forming galaxies.

We investigate the chromospheric evaporation in the flare of 2007 January 16 using line profiles observed by the Exterme-UV Imaging Spectrometer on board Hinode. Three points at flare ribbons of different magnetic polarities are analyzed in detail. We find that the three points show different patterns of upflows and downflows in the impulsive phase of the flare. The spectral lines at the first point are mostly blueshifted, with the hotter lines showing a dominant blueshifted component over the stationary one. At the second point, however, only weak upflows are detected; instead, notable downflows appear at high temperatures (up to 2.5–5.0 MK). The third point is similar to the second one only in that it shows evidence of multi-component downflows. While the evaporated plasma falling back down as warm rain is a possible cause of the redshifts at the second and third points, the different patterns of chromospheric evaporation at the three points imply the existence of different heating mechanisms in the flaring active region.

We present the detection of multiple high-velocity silicon monoxide (SiO v = 1, 2, J = 1–0) maser features in the high-mass protostar W51 North which are distributed over an exceedingly large velocity range from 105 to 230 km s⁻¹. The SiO v = 1, J = 1–0 maser emission shows 3–5 narrow components which span a velocity range from 154 to 230 km s⁻¹ according to observational epochs. The SiO v = 2, J = 1–0 maser also shows 3–5 narrow components that do not correspond to the SiO v = 1 maser and span a velocity range from 105 to 154 km s⁻¹. The multiple maser components show significant changes on very short timescales (<1 month) from epoch to epoch. We suggest that the high-velocity SiO masers may be emanated from massive star-forming activity of the W51 North protostar as SiO maser jets and will be a good probe of the earliest evolutionary stages of high-mass star formation via an accretion model. Further high angular resolution observations will be required for confirmation.

We analyze archival HST/STIS/FUV-MAMA imaging and spectroscopy of 13 compact star clusters within the circumnuclear starburst region of M83, the closest such example. We compare the observed spectra with semi-empirical models, which are based on an empirical library of Galactic O and B stars observed with IUE, and with theoretical models, which are based on a new theoretical UV library of hot massive stars computed with WM-Basic. The models were generated with Starburst99 for metallicities of Z = 0.020 and Z = 0.040, and for stellar initial mass functions (IMFs) with upper mass limits of 10, 30, 50, and 100 M_☉. We estimate the ages and masses of the clusters from the best-fit model spectra and find that the ages derived from the semi-empirical and theoretical models agree within a factor of 1.2 on average. A comparison of the spectroscopic age estimates with values derived from HST/WFC3/UVIS multi-band photometry shows a similar level of agreement for all but one cluster. The clusters have a range of ages from about 3 to 20 Myr and do not appear to have an age gradient along M83's starburst. Clusters with strong P-Cygni profiles have masses of a few×10⁴ M_☉, seem to have formed stars more massive than 30 M_☉, and are consistent with a Kroupa IMF from 0.1to100 M_☉. Field regions in the starburst lack P-Cygni profiles and are dominated by B stars.

We present a new implementation of the MHD relaxation method for reconstruction of the nearly force-free coronal magnetic field from a photospheric vector magnetogram. A new numerical MHD scheme is proposed to solve the full MHD equations by using the spacetime conservation-element and solution-element method. The bottom boundary condition is prescribed in a similar way as in the stress-and-relax method, by changing the transverse field incrementally to match the magnetogram, and other boundaries of the computational box are set by the nonreflecting boundary conditions. Applications to the well-known benchmarks for nonlinear force-free-field reconstruction, the Low & Lou force-free equilibria, validate the method and confirm its capability for future practical application, with observed magnetograms as inputs.

The Anglo-Australian Planet Search has now accumulated 12 years of radial-velocity data with long-term instrumental precision better than 3 m s⁻¹. In this paper, we expand on earlier simulation work, to probe the frequency of near-circular, long-period gas-giant planets residing at orbital distances of 3–6 AU—the so-called Jupiter analogs. We present the first comprehensive analysis of the frequency of these objects based on radial-velocity data. We find that 3.3% of stars in our sample host Jupiter analogs; detailed, star-by-star simulations show that no more than 37% of stars host a giant planet between 3 and 6 AU.

We present 12 years of precision Doppler data for the very nearby G3 star HD 102365, which reveals the presence of a Neptune-like planet with a 16.0 M_Earth minimum mass in a 122.1 day orbit. Very few "Super Earth" planets have been discovered to date in orbits this large and those that have been found reside in multiple systems of between three and six planets. HD 102365 b, in contrast, appears to orbit its star in splendid isolation. Analysis of the residuals to our Keplerian fit for HD 102365 b indicates that there are no other planets with minimum mass above 0.3 M_Jup orbiting within 5 AU and no other "Super Earths" more massive than 10 M_Earth orbiting at periods shorter than 50 days. At periods of less than 20 days these limits drop to as low as 6 M_Earth. There are now 32 exoplanets known with minimum mass below 20 M_Earth, and interestingly the period distributions of these low-mass planets seem to be similar whether they orbit M-, K-, or G-type dwarfs.

Shock breakout is the earliest, readily observable emission from a core-collapse supernova (SN) explosion. Observing SN shock breakout may yield information about the nature of the SN shock prior to exiting the progenitor and, in turn, about the core-collapse SN mechanism itself. X-ray outburst 080109, later associated with SN 2008D, is a very well-observed example of shock breakout from a core-collapse SN. Despite excellent observational coverage and detailed modeling, fundamental information about the shock breakout, such as the radius of breakout and driver of the light curve timescale, is still uncertain. The models constructed for explaining the shock breakout emission from SN 2008D all assume spherical symmetry. We present a study of the observational characteristics of aspherical shock breakout from stripped-envelope core-collapse SNe surrounded by a wind. We conduct two-dimensional, jet-driven SN simulations from stripped-envelope progenitors and calculate the resulting shock breakout X-ray spectra and light curves. The X-ray spectra evolve significantly in time as the shocks expand outward and are not fit well by single-temperature and radius blackbodies. The timescale of the X-ray burst light curve of the shock breakout is related to the shock crossing time of the progenitor, and not to the much shorter light crossing time that sets the light curve timescale in spherical breakouts. This could explain the long shock breakout light curve timescale observed for XRO 080109/SN 2008D. We also comment on the distribution of intermediate-mass elements in asymmetric explosions.

We present X-ray, infrared, optical, and radio observations of four previously unidentified Galactic plane X-ray sources: AX J163252–4746, AX J184738–0156, AX J144701–5919, and AX J144547–5931. Detection of each source with the Chandra X-ray Observatory has provided sub-arcsecond localizations, which we use to identify bright infrared counterparts to all four objects. Infrared and optical spectroscopy of these counterparts demonstrate that all four X-ray sources are extremely massive stars, with spectral classifications: Ofpe/WN9 (AX J163252–4746), WN7 (AX J184738–0156 = WR121a), WN7–8h (AX J144701–5919), and OIf⁺ (AX J144547–5931). AX J163252–4746 and AX J184738–0156 are both luminous, hard, X-ray emitters with strong Fe xxv emission lines in their X-ray spectra at ∼6.7 keV. The multi-wavelength properties of AX J163252–4746 and AX J184738–0156 are not consistent with isolated massive stars or accretion onto a compact companion; we conclude that their X-ray emission is most likely generated in a colliding-wind binary (CWB) system. For both AX J144701–5919 and AX J144547–5931, the X-ray emission is an order of magnitude less luminous and with a softer spectrum. These properties are consistent with a CWB interpretation for these two sources also, but other mechanisms for the generation of X-rays cannot be excluded. There are many other as yet unidentified X-ray sources in the Galactic plane, with X-ray properties similar to those seen for AX J163252–4746, AX J184738–0156, AX J144701–5919, and AX J144547–5931. This may indicate a substantial population of X-ray-emitting massive stars and CWBs in the Milky Way.

Based on the characteristics of the magnetorotational instability (MRI) and the MRI-driven turbulence, we construct a steady model for a geometrically thin disk using "non-standard" α-prescription. The efficiency of the angular momentum transport depends on the magnetic Prandtl number, Pm = ν/η, where ν and η are the microscopic viscous and magnetic diffusivities. In our disk model, Shakura–Sunyaev's α-parameter has a power-law dependence on the magnetic Prandtl number, that is α ∝ Pm^δ, where δ is the constant power-law index. Adopting Spitzer's microscopic diffusivities, the magnetic Prandtl number becomes a decreasing function of the disk radius when δ>0. The transport efficiency of the angular momentum and the viscous heating rate are thus smaller in the outer part of the disk, while these are impacted by the size of index δ. We find that the disk becomes more unstable to the gravitational instability for a larger value of index δ. The most remarkable feature of our disk model is that the thermal and secular instabilities can grow in its middle part even if the radiation pressure is negligibly small in the condition δ>2/3. In the realistic disk systems, it would be difficult to maintain the steady mass accretion state unless the Pm dependence of MRI-driven turbulence is relatively weak.

The rate evolution of subluminous Type Ia supernovae (SNe Ia) is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly declining light curves of the observed SN Ia population here defined by low-stretch values (s ⩽ 0.8). Up to redshift z = 0.6, we find 18 photometrically identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behavior is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass-dependent behavior: r(z) = A × M_g, with A = (1.1 ± 0.3) × 10⁻¹⁴ SNe yr⁻¹M⁻¹_☉.

Dwarf stars are believed to have a small protostar disk where planets may grow up. During the planet formation stage, embryos undergoing type I migration are expected to be stalled at an inner edge of the magnetically inactive disk (a_crit ∼ 0.2–0.3 AU). This mechanism makes the location around a_crit a "sweet spot" for forming planets. In dwarf stars with masses ∼0.5 M_☉, a_crit is roughly inside the habitable zone of the system. In this paper, we study the formation of habitable planets due to this mechanism using model system OGLE-06-109L, which has a 0.51 M_☉ dwarf star with two giant planets in 2.3 and 4.6 AU observed by microlensing. We model the embryos undergoing type I migration in the gas disk with a constant disk-accretion rate ($\dot{M}$). Giant planets in outside orbits affect the formation of habitable planets through secular perturbations at the early stage and secular resonance at the late stage. We find that the existence and the masses of the habitable planets in the OGLE-06-109L system depend on both $\dot{M}$ and the speed of type I migration. If planets are formed earlier, so that $\dot{M}$ is larger (∼10⁻⁷ M_☉ yr⁻¹), terrestrial planets cannot survive unless the type I migration rate is an order of magnitude less. If planets are formed later, so that $\dot{M}$ is smaller (∼10⁻⁸ M_☉ yr⁻¹), single and high-mass terrestrial planets with high water contents (∼5%) will be formed by inward migration of outer planet cores. A slower-speed migration will result in several planets via collisions of embryos, and thus their water contents will be low (∼2%). Mean motion resonances or apsidal resonances among planets may be observed if multiple planets survive in the inner system.

The origin and progenitors of short–hard gamma-ray bursts (GRBs) remain a puzzle and a highly debated topic. Recent Swift observations suggest that these GRBs may be related to catastrophic explosions in degenerate compact stars, denoted as "Type I" GRBs. The most popular models include the merger of two compact stellar objects (NS–NS or NS–BH). We utilize a Monte Carlo approach to determine whether a merger progenitor model can self-consistently account for all the observations of short–hard GRBs, including a sample with redshift measurements in the Swift era (z-known sample) and the CGRO/BATSE sample. We apply various merger time delay distributions invoked in compact star merger models to derive the redshift distributions of these Type I GRBs, and then constrain the unknown luminosity function of Type I GRBs using the observed luminosity–redshift (L–z) distributions of the z-known sample. The best luminosity function model, together with the adopted merger delay model, is then applied to confront the peak flux distribution (log N–log P distribution) of the BATSE and Swift samples. We find that for all the merger models invoking a range of merger delay timescales (including those invoking a large fraction of "prompt mergers"), it is difficult to reconcile the models with all the data. The data are instead statistically consistent with the following two possible scenarios. First, that short/hard GRBs are a superposition of compact-star–merger–origin (Type I) GRBs and a population of GRBs that track the star formation history, which are probably related to the deaths of massive stars (Type II GRBs). Second, the entire short/hard GRB population is consistent with a typical delay of 2 Gyr with respect to the star formation history with modest scatter. This may point toward a different Type I progenitor than the traditional compact star merger models.

We report results from numerical simulations of star formation in the early universe that focus on the dynamical behavior of metal-free gas under different initial and environmental conditions. In particular we investigate the role of turbulence, which is thought to ubiquitously accompany the collapse of high-redshift halos. We distinguish between two main cases: the birth of Population III.1 stars—those which form in the pristine halos unaffected by prior star formation—and the formation of Population III.2 stars—those forming in halos where the gas has an increased ionization fraction. We find that turbulent primordial gas is highly susceptible to fragmentation in both cases, even for turbulence in the subsonic regime, i.e., for rms velocity dispersions as low as 20% of the sound speed. Fragmentation is more vigorous and more widespread in pristine halos compared to pre-ionized ones. If such levels of turbulent motions were indeed present in star-forming minihalos, Population III.1 stars would be on average of somewhat lower mass, and form in larger groups, than Population III.2 stars. We find that fragment masses cover over two orders of magnitude, suggesting that the Population III initial mass function may have been much broader than previously thought. This prompts the need for a large, high-resolution study of the formation of dark matter minihalos that is capable of resolving the turbulent flows in the gas at the moment when the baryons become self-gravitating. This would help to determine the applicability of our results to primordial star formation.

We investigate mass-dependent galaxy evolution based on a large sample of (more than 50,000) K-band selected galaxies in a multi-wavelength catalog of the Subaru/XMM-Newton Deep Survey and the UKIRT Infrared Deep Sky Survey/Ultra Deep Survey. We employ optical to near-infrared photometry to determine photometric redshifts of these galaxies. Then, we estimate the stellar mass of our sample galaxies using a standard fitting procedure as we used for estimation of the photometric redshift. From the sample galaxies, we obtain the stellar mass function of galaxies and the cosmic stellar mass density up to z ∼ 4. Our results are consistent with previous studies and we find a considerable number of low-mass galaxies (M_* ∼ 10^10.5) at the redshift range 3 < z < 4. By combining stellar masses and spatial distributions of galaxies derived from a large number of galaxies in the contiguous wide and deep field, we examine properties of the mass-dependent clustering of galaxies. The correlation functions of our sample galaxies show clear evolution and they connect to that in the local universe consistently. Also, we find that the massive galaxies show strong clustering throughout our studied redshift range. The correlation length of massive galaxies rapidly decreases from z = 4 to 2. The mass of dark halos hosting the intermediate-mass value galaxies changes from high (10¹⁴ M_☉) to low (10¹³ M_☉) with decreasing redshift at around z ∼ 2. We also find some high-mass density regions of massive galaxies at 1.4 ⩽ z < 2.5 in our sample. These concentrations of massive galaxies may be candidate progenitors of the present-day clusters of galaxies. At this redshift range, massive star-forming galaxies are the dominant population making up the structures and the passively evolving galaxies show stronger clustering and they may have formed earlier than those star-forming galaxies.

Motivated both by considerations of the generation of large-scale astrophysical magnetic fields and by potential problems with mean magnetic field generation by turbulent convection, we investigate the mean electromotive force (emf) resulting from the magnetic buoyancy instability of a rotating layer of stratified magnetic field, considering both unidirectional and sheared fields. We discuss why the traditional decomposition into α and β effects is inappropriate in this case, and that it is only consideration of the entire mean emf that is meaningful. By considering a weighted average of the unstable linear eigenmodes, and averaging over the horizontal plane, we obtain depth-dependent emfs. For the simplified case of isothermal, ideal MHD, we are able to obtain an analytic expression for the emf; more generally, the emf has to be determined numerically. We calculate how the emf depends on the various parameters of the problem, particularly the rotation rate and the latitude of the magnetic layer.

The explosive Becklin–Neugebauer (BN)/Kleinman–Low (KL) outflow emerging from OMC1 behind the Orion Nebula may have been powered by the dynamical decay of a non-hierarchical multiple system ∼500 years ago that ejected the massive stars I, BN, and source n, with velocities of about 10–30 km s⁻¹. New proper-motion measurements of H₂ features show that within the errors of measurement, the outflow originated from the site of stellar ejection. Combined with published data, these measurements indicate an outflow age of ∼500 years, similar to the time since stellar ejection. The total kinetic energy of the ejected stars and the outflow is about 2 to 6 × 10⁴⁷ erg. It is proposed that the gravitational potential energy released by the formation of a short-period binary, most likely source I, resulted in stellar ejection and powered the outflow. A scenario is presented for the formation of a compact, non-hierarchical multiple star system, its decay into an ejected binary and two high-velocity stars, and launch of the outflow. Three mechanisms may have contributed to the explosion in the gas: (1) unbinding of the circumcluster envelope following stellar ejection, (2) disruption of circumstellar disks and high-speed expulsion of the resulting debris during the final stellar encounter, and (3) the release of stored magnetic energy. Plausible protostellar disk end envelope properties can produce the observed outflow mass, velocity, and kinetic energy distributions. The ejected stars may have acquired new disks by fall-back or Bondi–Hoyle accretion with axes roughly orthogonal to their velocities. The expulsion of gas and stars from OMC1 may have been driven by stellar interactions.

We present Cygnus X in a new multi-wavelength perspective based on an unbiased BLAST survey at 250, 350, and 500 μm, combined with rich data sets for this well-studied region. Our primary goal is to investigate the early stages of high-mass star formation. We have detected 184 compact sources in various stages of evolution across all three BLAST bands. From their well-constrained spectral energy distributions, we obtain the physical properties mass, surface density, bolometric luminosity, and dust temperature. Some of the bright sources reaching 40 K contain well-known compact H ii regions. We relate these to other sources at earlier stages of evolution via the energetics as deduced from their position in the luminosity–mass (L–M) diagram. The BLAST spectral coverage, near the peak of the spectral energy distribution of the dust, reveals fainter sources too cool (∼10 K) to be seen by earlier shorter-wavelength surveys like IRAS. We detect thermal emission from infrared dark clouds and investigate the phenomenon of cold "starless cores" more generally. Spitzer images of these cold sources often show stellar nurseries, but these potential sites for massive star formation are "starless" in the sense that to date there is no massive protostar in a vigorous accretion phase. We discuss evolution in the context of the L–M diagram. Theory raises some interesting possibilities: some cold massive compact sources might never form a cluster containing massive stars, and clusters with massive stars might not have an identifiable compact cold massive precursor.

We present a spatially resolved near-UV/optical study, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope, of NGC 4150, a sub-L_*, early-type galaxy (ETG) of around 6 × 10⁹M_☉, which has been observed as part of the WFC3 Early-Release Science Programme. Previous work indicates that this galaxy has a large reservoir of molecular hydrogen gas, exhibits a kinematically decoupled core (a likely indication of recent merging) and strong, central Hβ absorption (indicative of young stars). While relatively uninspiring in its optical image, the core of NGC 4150 shows ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of near-UV/optical colors that are similar to those of nearby E+A (post-starburst) galaxies and lie between those of M83 (an actively star-forming spiral) and the local quiescent ETG population. We parameterize the properties of the recent star formation (RSF; age, mass fraction, metallicity, and internal dust content) in the NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar models. The typical age of the RSF is around 0.9 Gyr, consistent with the similarity of the near-UV colors to post-starburst systems, while the morphological structure of the young component supports the proposed merger scenario. The typical RSF metallicity, representative of the metallicity of the gas fuelling star formation, is ∼0.3–0.5 Z_☉. Assuming that this galaxy is a merger and that the gas is sourced mainly from the infalling companion, these metallicities plausibly indicate the gas-phase metallicity (GPM) of the accreted satellite. Comparison to the local mass–GPM relation suggests (crudely) that the mass of the accreted system is ∼3 × 10⁸M_☉, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF mass fractions indicates that the RSF contributes ∼2%–3% of the stellar mass. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of ETGs at late epochs.

We explore whether global observed properties, specifically half-light radii, mean surface brightness, and integrated stellar kinematics, suffice to unambiguously differentiate galaxies from star clusters, which presumably formed differently and lack dark matter halos. We find that star clusters lie on the galaxy scaling relationship referred to as the fundamental manifold (FM), on the extension of a sequence of compact galaxies, and so conclude that there is no simple way to differentiate star clusters from ultracompact galaxies. By extending the validity of the FM over a larger range of parameter space and a wider set of objects, we demonstrate that the physics that constrains the resulting baryon and dark matter distributions in stellar systems is more general than previously appreciated. The generality of the FM implies (1) that the stellar spatial distribution and kinematics of one type of stellar system do not arise solely from a process particular to that set of systems, such as violent relaxation for elliptical galaxies, but are instead the result of an interplay of all processes responsible for the generic settling of baryons in gravitational potential wells, (2) that the physics of how baryons settle is independent of whether the system is embedded within a dark matter halo, and (3) that peculiar initial conditions at formation or stochastic events during evolution do not ultimately disturb the overall regularity of baryonic settling. We also utilize the relatively simple nature of star clusters to relate deviations from the FM to the age of the stellar population and find that stellar population models systematically and significantly overpredict the mass-to-light ratios of old, metal-rich clusters. We present an empirical calibration of stellar population mass-to-light ratios with age and color. Finally, we use the FM to estimate velocity dispersions for the low surface brightness, outer halo clusters that lack such measurements.

We present new precise HIRES radial velocity (RV) data sets of five nearby stars obtained at Keck Observatory. HD 31253, HD 218566, HD 177830, HD 99492, and HD 74156 are host stars of spectral classes F through K and show RV variations consistent with new or additional planetary companions in Keplerian motion. The orbital parameters of the candidate planets in the five planetary systems span minimum masses of $\mathcal {M}\sin i = 27.43 \;\mathcal {M}_\oplus$ to $8.28 \;\mathcal {M}_{J}$, periods of 17.05–4696.95 days and eccentricities ranging from circular to extremely eccentric (e ≈ 0.63). The fifth star, HD 74156, was known to have both a 52 day and a 2500 day planet, and was claimed to also harbor a third planet at 336 days, in apparent support of the "Packed Planetary System" hypothesis. Our greatly expanded data set for HD 74156 provides strong confirmation of both the 52 day and 2500 day planets, but strongly contradicts the existence of a 336 day planet, and offers no significant evidence for any other planets in the system.

We present a new method for constructing three-dimensional mass maps from gravitational lensing shear data. We solve the lensing inversion problem using truncation of singular values (within the context of generalized least-squares estimation) without a priori assumptions about the statistical nature of the signal. This singular value framework allows a quantitative comparison between different filtering methods: we evaluate our method beside the previously explored Wiener-filter approaches. Our method yields near-optimal angular resolution of the lensing reconstruction and allows cluster sized halos to be de-blended robustly. It allows for mass reconstructions which are two to three orders of magnitude faster than the Wiener-filter approach; in particular, we estimate that an all-sky reconstruction with arcminute resolution could be performed on a timescale of hours. We find however that linear, non-parametric reconstructions have a fundamental limitation in the resolution achieved in the redshift direction.

The Coma Cluster of galaxies hosts the brightest radio halo known and has therefore been the target of numerous searches for associated inverse Compton (IC) emission, particularly at hard X-ray energies where the IC signal must eventually dominate over thermal emission. The most recent search with the Suzaku Hard X-ray Detector failed to confirm previous IC detections with RXTE and BeppoSAX, instead setting an upper limit 2.5 times below their non-thermal flux. However, this discrepancy can be resolved if the IC emission is very extended, beyond the scale of the cluster radio halo. Using reconstructed sky images from the 58-month Swift Burst Alert Telescope (BAT) all-sky survey, the feasibility of such a solution is investigated. Building on Renaud et al., we test and implement a method for extracting the fluxes of extended sources, assuming specified spatial distributions. BAT spectra are jointly fit with an XMM-Newton EPIC-pn spectrum derived from mosaic observations. We find no evidence for large-scale IC emission at the level expected from the previously detected non-thermal fluxes. For all non-thermal spatial distributions considered, which span the gamut of physically reasonable IC models, we determine upper limits for which the largest (most conservative) limit is ≲4.2 × 10⁻¹² erg s⁻¹ cm⁻² (20–80 keV), which corresponds to a lower limit on the magnetic field B > 0.2 μ G. A nominal flux upper limit of <2.7 × 10⁻¹² erg s⁻¹ cm⁻², with corresponding B > 0.25 μ G, is derived for the most probable IC distribution given the size of the radio halo and likely magnetic field radial profile.

This paper applies a soft-sphere distinct element method Granular Dynamics code to simulate asteroid regolith and rubble piles. Applications to regolith studies in low gravity are also studied. Then an algorithm to calculate self-gravity is derived and incorporated for full-scale simulations of rubble-pile asteroids using Granular Dynamics techniques. To test its validity, the algorithm's results are compared with the exact direct calculation of the gravitational forces. Further avenues to improve the performance of the algorithm are also discussed.

We investigate the propagation of ∼0.3–300 keV electrons in five solar impulsive electron events, observed by the WIND three-dimensional Plasma and Energetic Particle instrument, that have rapid-rise and rapid-decay temporal profiles. In two events, the temporal profiles above 25 keV show a second peak of inward-traveling electrons tens of minutes after the first peak, followed by a third peak due to outward-traveling electrons minutes later—likely due to reflection/scattering first at ∼0.7–1.7 AU past the Earth, and then in the inner heliosphere inside 1 AU. In the five events, below a transition energy E₀ (∼10–40 keV), the pitch-angle distributions are highly anisotropic with a pitch-angle width at half-maximum (PAHM) of <15° (unresolved) through the time of the peak; the ratio Λ of the peak flux of scattered (225–90° relative to the outward direction) to field-aligned scatter-free (0°–225) electrons is ≲0.1. Above E₀, the PAHM at the flux peak increases with energy up to 85° at 300 keV, and Λ also increases with energy up to ∼0.8 at 300 keV. Thus, low-energy electrons propagated essentially scatter-free through the interplanetary medium, while high-energy electrons experienced pitch-angle scattering, with scattering strength increasing with energy. The transition energy E₀ between the two populations is always such that the electron gyroradius (ρ_e) is approximately equal to the local thermal proton gyroradius (ρ_Tp), suggesting that the higher energy electrons were scattered by resonance with turbulent fluctuations at scale ≳ρ_Tp in the solar wind.

A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10° 2179, BD−9° 4395, and LS IV+6° 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres were computed with H, He, C, N, O, and Ne treated in NLTE. Model atmosphere parameters were chosen from consideration of fits to observed He i line profiles and ionization equilibria of C and N ions. The program SYNSPEC was then used to determine the NLTE abundances for Ne as well as H, He, C, N, and O. LTE neon abundances from Ne i lines in the EHes: LSE 78, V1920 Cyg, HD 124448, and PV Tel, are derived from published models and an estimate of the NLTE correction applied to obtain the NLTE Ne abundance. We show that the derived abundances of these key elements, including Ne, are well matched with semi-quantitative predictions for the EHe resulting from a cold merger (i.e., no nucleosynthesis during the merger) of an He white dwarf with a C–O white dwarf.

We have simulated a Galactic population of young pulsars and compared with the Fermi LAT sample, constraining the birth properties, beaming and evolution of these spin-powered objects. Using quantitative tests of agreement with the distributions of observed spin and pulse properties, we find that short birth periods P₀ ≈ 50 ms and γ-ray beams arising in the outer magnetosphere, dominated by a single pole, are strongly preferred. The modeled relative numbers of radio-detected and radio-quiet objects agrees well with the data. Although the sample is local, extrapolation to the full Galaxy implies a γ-ray pulsar birthrate 1/(59 yr). This is shown to be in good agreement with the estimated Galactic core collapse rate and with the local density of OB star progenitors. We give predictions for the numbers of expected young pulsar detections if Fermi LAT observations continue 10 years. In contrast to the potentially significant contribution of unresolved millisecond pulsars, we find that young pulsars should contribute little to the Galactic γ-ray background.

Swift X-ray observations of the ∼60 day supersoft phase of the recurrent nova RS Ophiuchi (RS Oph) 2006 show the progress of nuclear burning on the white dwarf (WD) in exquisite detail. First seen 26 days after the optical outburst, this phase started with extreme variability likely due to variable absorption, although intrinsic WD variations are not excluded. About 32 days later, a steady decline in count rate set in. NLTE model atmosphere spectral fits during the supersoft phase show that the effective temperature of the WD increases from ∼65 eV to ∼90 eV during the extreme variability phase, falling slowly after about day 60 and more rapidly after day 80. The bolometric luminosity is seen to be approximately constant and close to Eddington from day 45 up to day 60, the subsequent decline possibly signaling the end of extensive nuclear burning. Before the decline, a multiply-periodic ∼35 s modulation of the soft X-rays was present and may be the signature of a nuclear fusion driven instability. Our measurements are consistent with a WD mass near the Chandrasekhar limit; combined with a deduced accumulation of mass transferred from its binary companion, this leads us to suggest that RS Oph is a strong candidate for a future supernova explosion. The main uncertainty now is whether the WD is the CO type necessary for a Type Ia supernova. This may be confirmed by detailed abundance analyses of spectroscopic data from the outbursts.

We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity, leading to an estimate of the tidal Love number and an assessment of the degree of central concentration in the planetary interior. An initial ground-based secondary-eclipse phase reported by López-Morales et al. (0.510 ± 0.002) implied eccentricity at the 4.5σ level. The spectroscopic orbit of Hebb et al. has eccentricity 0.049 ± 0.015, a 3σ result, implying an eclipse phase of 0.509 ± 0.007. However, there is a well-documented tendency of spectroscopic data to overestimate small eccentricities. Our eclipse phases are 0.5010 ± 0.0006 (3.6 and 5.8 μm) and 0.5006 ± 0.0007 (4.5 and 8.0 μm). An unlikely orbital precession scenario invoking an alignment of the orbit during the Spitzer observations could have explained this apparent discrepancy, but the final eclipse phase of López-Morales et al. (0.510 ±^+0.007_−0.006) is consistent with a circular orbit at better than 2σ. An orbit fit to all the available transit, eclipse, and radial-velocity data indicates precession at <1σ; a non-precessing solution fits better. We also comment on analysis and reporting for Spitzer exoplanet data in light of recent re-analyses.

The densities in the outer regions of clusters of galaxies are very low, and the collisional timescales are very long. As a result, heavy elements will be under-ionized after they have passed through the accretion shock. We have studied systematically the effects of non-equilibrium ionization for relaxed clusters in the ΛCDM cosmology using one-dimensional hydrodynamic simulations. We found that non-equilibrium ionization effects do not depend on cluster mass, but depend strongly on redshift which can be understood by self-similar scaling arguments. The effects are stronger for clusters at lower redshifts. We present X-ray signatures such as surface brightness profiles and emission lines in detail for a massive cluster at low redshift. In general, soft emission (0.3–1.0 keV) is enhanced significantly by under-ionization, and the enhancement can be nearly an order of magnitude near the shock radius. The most prominent non-equilibrium ionization signature we found is the O vii and O viii line ratio. The ratios for non-equilibrium ionization and collisional ionization equilibrium models are different by more than an order of magnitude at radii beyond half of the shock radius. These non-equilibrium ionization signatures are equally strong for models with different non-adiabatic shock electron heating efficiencies. We have also calculated the detectability of the O vii and O viii lines with the future International X-ray Observatory (IXO). Depending on the line ratio measured, we conclude that an exposure of ∼130–380 ks on a moderate-redshift, massive regular cluster with the X-ray Microcalorimeter Spectrometer (XMS) on the IXO will be sufficient to provide a strong test for the non-equilibrium ionization model.

In this paper, we introduce the concept of direct statistical simulation for astrophysical flows. This technique may be appropriate for problems in astrophysical fluids where the instantaneous dynamics of the flows are of secondary importance to their statistical properties. We give examples of such problems including mixing and transport in planets, stars, and disks. The method is described for a general set of evolution equations, before we consider the specific case of a spectral method optimized for problems on a spherical surface. The method is illustrated for the simplest non-trivial example of hydrodynamics and magnetohydrodynamics on a rotating spherical surface. We then discuss possible extensions of the method both in terms of computational methods and the range of astrophysical problems that are of interest.

We reconsider the contribution that singly protonated polycyclic aromatic hydrocarbons (PAHs; HPAH⁺s) might make to the Class A component of the 6.2 μm interstellar emission feature in light of the recent experimental measurements of protonated naphthalene and coronene. Our calculations on the small HPAH⁺s have a band near 6.2 μm, as found in experiment. While the larger HPAH⁺s still have emission near 6.2 μm, the much larger intensity of the band near 6.3 μm overwhelms the weaker band at 6.2 μm, so that the 6.2 μm band is barely visible. Since the large PAHs are more representative of those in the interstellar medium, our work suggests that large HPAH⁺s cannot be major contributors to the observed emission at 6.2 μm (i.e., Class A species). Saturating large PAH cations with hydrogen atoms retains the 6.2 μm Class A band position, but the rest of the spectrum is inconsistent with observed spectra.

We report on the γ-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) γ-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 ± 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 ± 0.14, and the softest one is 2.51 ± 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15—August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size ≲0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15–43 GHz), and that the total jet power (≃10⁴⁴ erg s⁻¹) constitutes only a small fraction (∼10⁻³) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV–10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude.

We present a study of reddening and absorption toward the narrow line regions (NLRs) in active galactic nuclei (AGNs) selected from the Revised Shapley-Ames, 12 μm, and Swift/Burst Alert Telescope samples. For the sources in host galaxies with inclinations of b/a > 0.5, we find that the mean ratio of [O iii] λ5007, from ground-based observations, and [O iv] 28.59 μm, from Spitzer/Infrared Spectrograph observations, is a factor of two lower in Seyfert 2s than Seyfert 1s. The combination of low [O iii]/[O iv] and [O iii] λ4363/λ5007 ratios in Seyfert 2s suggests more extinction of emission from the NLR than in Seyfert 1s. Similar column densities of dusty gas, N_H∼ several × 10²¹ cm⁻², can account for the suppression of both [O iii] λ5007 and [O iii] λ4363, as compared to those observed in Seyfert 1s. Also, we find that the X-ray line O vii λ22.1 Å is weaker in Seyfert 2s, consistent with absorption by the same gas that reddens the optical emission. Using a Hubble Space Telescope/Space Telescope Imaging Spectrograph slitless spectrum of the Seyfert 1 galaxy NGC 4151, we estimate that only ∼30% of the [O iii] λ5007 comes from within 30 pc of the central source, which is insufficient to account for the low [O iii]/[O iv] ratios in Seyfert 2s. If Seyfert 2 galaxies have similar intrinsic [O iii] spatial profiles, the external dusty gas must extend further out along the NLR, perhaps in the form of nuclear dust spirals that have been associated with fueling flows toward the AGN.

We present a statistical analysis of the X-ray luminosity of rotation-powered pulsars and their surrounding nebulae using the sample of Kargaltsev & Pavlov, and we complement this with an analysis of the γ-ray emission of Fermi-detected pulsars. We report a strong trend in the efficiency with which spin-down power is converted to X-ray and γ-ray emission with characteristic age: young pulsars and their surrounding nebulae are efficient X-ray emitters, whereas in contrast old pulsars are efficient γ-ray emitters. We divided the X-ray sample in a young (τ_c < 1.7 × 10⁴ yr) and old sample and used linear regression to search for correlations between the logarithm of the X-ray and γ-ray luminosities and the logarithms of the periods and period derivatives. The X-ray emission from young pulsars and their nebulae are both consistent with $L_X \propto \dot{P}^3/P^6$. For old pulsars and their nebulae the X-ray luminosity is consistent with a more or less constant efficiency $\eta \equiv L_X/\dot{E}_{{\rm rot}} \approx 8\times 10^{-5}$. For the γ-ray luminosity we confirm that $L_\gamma \propto \sqrt{\vphantom{A^A}\smash{\hbox{${\dot{E}_{{\rm rot}}}$}}}$. We discuss these findings in the context of pair production inside pulsar magnetospheres and the striped wind model. We suggest that the striped wind model may explain the similarity between the X-ray properties of the pulsar wind nebulae and the pulsars themselves, which according to the striped wind model may both find their origin outside the light cylinder, in the pulsar wind zone.

GRB 100418A is a long gamma-ray burst (GRB) at redshift z = 0.6235 discovered with the Swift Gamma-ray Burst Explorer with unusual optical and X-ray light curves. After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least ∼7 × 10³ s after the trigger, peak at ∼5 × 10⁴ s, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in GRB afterglows. Observations with Rapid Eye Mount during a gap in the Swift coverage indicate a bright optical flare at ∼2.5 × 10⁴ s. The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the jet of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is ⩾10² times the 10⁵¹ erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis jet model would require the intrinsic T₉₀ for the GRB jet viewed on-axis to be very short, ∼10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs. The non-detection of a jet break up to t ∼ 2 × 10⁶ s indicates a jet half-opening angle of at least ∼14°, and a relatively high-collimation-corrected jet energy of E_jet ⩾ 10⁵² erg.