Table of contents

We present a high-resolution, multi-wavelength study of the massive protostellar cluster NGC 6334 I(N) that combines new spectral line data from the Submillimeter Array (SMA) and VLA with a re-analysis of archival VLA continuum data, Two Micron All Sky Survey and Spitzer images. As shown previously, the brightest 1.3 mm source SMA1 contains substructure at subarcsecond resolution, and we report the first detection of SMA1b at 3.6 cm along with a new spatial component at 7 mm (SMA1d). We find SMA1 (aggregate of sources a, b, c, and d) and SMA4 to be comprised of free–free and dust components, while SMA6 shows only dust emission. Our 15 resolution 1.3 mm molecular line images reveal substantial hot-core line emission toward SMA1 and to a lesser degree SMA2. We find CH₃OH rotation temperatures of 165 ± 9 K and 145 ± 12 K for SMA1 and SMA2, respectively. We estimate a diameter of 1400 AU for the SMA1 hot-core emission, encompassing both SMA1b and SMA1d, and speculate that these sources comprise a ≳800 AU separation binary that may explain the previously suggested precession of the outflow emanating from the SMA1 region. Compact line emission from SMA4 is weak, and none is seen toward SMA6. The LSR velocities of SMA1, SMA2, and SMA4 all differ by 1–2 km s⁻¹. Outflow activity from SMA1, SMA2, SMA4, and SMA6 is observed in several molecules including SiO(5–4) and IRAC 4.5 μm emission; 24 μm emission from SMA4 is also detected. Eleven water maser groups are detected, eight of which coincide with SMA1, SMA2, SMA4, and SMA6, while two others are associated with the Sandell source SM2. We also detect a total of 83 Class I CH₃OH 44 GHz maser spots which likely result from the combined activity of many outflows. Our observations paint the portrait of multiple young hot cores in a protocluster prior to the stage where its members become visible in the near-infrared.

We present a new method to retrieve molecular abundances and temperature profiles from exoplanet atmosphere photometry and spectroscopy. We run millions of one-dimensional (1D) atmosphere models in order to cover the large range of allowed parameter space. In order to run such a large number of models, we have developed a parametric pressure–temperature (P–T) profile coupled with line-by-line radiative transfer, hydrostatic equilibrium, and energy balance, along with prescriptions for non-equilibrium molecular composition and energy redistribution. The major difference from traditional 1D radiative transfer models is the parametric P–T profile, which essentially means adopting energy balance only at the top of the atmosphere and not in each layer. We see the parametric P–T model as a parallel approach to the traditional exoplanet atmosphere models that rely on several free parameters to encompass unknown absorbers and energy redistribution. The parametric P–T profile captures the basic physical features of temperature structures in planetary atmospheres (including temperature inversions), and fits a wide range of published P–T profiles, including those of solar system planets. We apply our temperature and abundance retrieval method to the atmospheres of two transiting exoplanets, HD 189733b and HD 209458b, which have the best Spitzer and Hubble Space Telescope data available. For HD 189733b, we find efficient day–night redistribution of energy in the atmosphere, and molecular abundance constraints confirming the presence of H₂O, CO, CH₄, and CO₂. For HD 209458b, we confirm and constrain the dayside thermal inversion in an average 1D temperature profile. We also report independent detections of H₂O, CO, CH₄, and CO₂ on the dayside of HD 209458b, based on six-channel Spitzer photometry. We report constraints for HD 189733b due to individual data sets separately; a few key observations are variable in different data sets at similar wavelengths. Moreover, a noticeably strong CO₂ absorption in one data set is significantly weaker in another. We must, therefore, acknowledge the strong possibility that the atmosphere is variable, both in its energy redistribution state and in the chemical abundances.

We present a numerical scheme for modeling unresolved turbulence in cosmological adaptive mesh refinement codes. As a first application, we study the evolution of turbulence in the intracluster medium (ICM) and in the core of a galaxy cluster. Simulations with and without subgrid scale (SGS) model are compared in detail. Since the flow in the ICM is subsonic, the global turbulent energy contribution at the unresolved length scales is smaller than 1% of the internal energy. We find that the production of turbulence is closely correlated with merger events occurring in the cluster environment, and its dissipation locally affects the cluster energy budget. Because of this additional source of dissipation, the core temperature is larger and the density is smaller in the presence of SGS turbulence than in the standard adiabatic run, resulting in a higher entropy core value.

We report the Fermi Large Area Telescope (LAT) discovery of high-energy (MeV/GeV) γ-ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10σ in 10 months of all-sky survey data. Following the detections of Cen A and Per A, this makes M87 the third radio galaxy seen with the LAT. The faint point-like γ-ray source has a >100 MeV flux of 2.45 (±0.63) × 10⁻⁸ photons cm⁻² s⁻¹ (photon index = 2.26 ± 0.13) with no significant variability detected within the LAT observation. This flux is comparable with the previous EGRET upper limit (<2.18 × 10⁻⁸ photons cm⁻² s⁻¹, 2σ), thus there is no evidence for a significant MeV/GeV flare on decade timescales. Contemporaneous Chandra and Very Long Baseline Array data indicate low activity in the unresolved X-ray and radio core relative to previous observations, suggesting M87 is in a quiescent overall level over the first year of Fermi-LAT observations. The LAT γ-ray spectrum is modeled as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the core. The resultant SSC spectrum extrapolates smoothly from the LAT band to the historical-minimum TeV emission. Alternative models for the core and possible contributions from the kiloparsec-scale jet in M87 are considered, and cannot be excluded.

Pitch-angle diffusion is a key process in the theory of charged particle scattering by turbulent magnetic plasmas. This process is usually assumed to be diffusive and can, therefore, be described by a pitch-angle diffusion or Fokker–Planck coefficient. This parameter controls the parallel spatial diffusion coefficient as well as the parallel mean free path of charged particles. In the present paper, we determine pitch-angle diffusion coefficients from numerical computer simulations. These results are then compared with results from analytical theories. Especially, we compare the simulations with quasilinear, second-order, and weakly nonlinear diffusion coefficients. Such a comparison allows the test of previous theories and will lead to an improved understanding of the mechanism of particle scattering.

We have measured the average radial (cell center to network boundary) profile of the continuum intensity contrast associated with supergranular flows using data from the Precision Solar Photometric Telescope at the Mauna Loa Solar Observatory. After removing the contribution of the network flux elements by the application of masks based on Ca ii K intensity and averaging over more than 10⁵ supergranular cells, we find a ∼0.1% decrease in red and blue continuum intensity from the supergranular cell centers outward, corresponding to a ∼1.0 K decrease in brightness temperature across the cells. The radial intensity profile may be caused either by the thermal signal associated with the supergranular flows or a variation in the packing density of unresolved magnetic flux elements. These are not unambiguously distinguished by the observations, and we raise the possibility that the network magnetic fields play an active role in supergranular scale selection by enhancing the radiative cooling of the deep photosphere at the cell boundaries.

The time delay between the formation of a population of stars and the onset of type Ia supernovae (SNe Ia) sets important limits on the masses and nature of SN Ia progenitors. Here, we use a new observational technique to measure this time delay by comparing the spatial distributions of SNe Ia to their local environments. Previous work attempted such analyses encompassing the entire host of each SN Ia, yielding inconclusive results. Our approach confines the analysis only to the relevant portions of the hosts, allowing us to show that even so-called prompt SNe Ia that trace star formation on cosmic timescales exhibit a significant delay time of 200–500 million years. This implies that either the majority of Ia companion stars have main-sequence masses less than 3 M_☉, or that most SNe Ia arise from double white dwarf binaries. Our results are also consistent with a SNe Ia rate that traces the white dwarf formation rate, scaled by a fixed efficiency factor.

The recent discoveries of massive planets on ultra-wide orbits of HR 8799 and Fomalhaut present a new challenge for planet formation theorists. Our goal is to figure out which of three giant planet formation mechanisms—core accretion (with or without migration), scattering from the inner disk, or gravitational instability—could be responsible for Fomalhaut b, HR 8799 b, c and d, and similar planets discovered in the future. This paper presents the results of numerical experiments comparing the long-period planet formation efficiency of each possible mechanism in model A star, G star, and M star disks. First, a simple core accretion simulation shows that planet cores forming beyond 35 AU cannot reach critical mass, even under the most favorable conditions one can construct. Second, a set of N-body simulations demonstrates that planet–planet scattering does not create stable, wide-orbit systems such as HR 8799. Finally, a linear stability analysis verifies previous work showing that global spiral instabilities naturally arise in high-mass disks. We conclude that massive gas giants on stable orbits with semimajor axes a ≳ 35 AU form by gravitational instability in the disk. We recommend that observers examine the planet detection rate as a function of stellar age, controlling for the planets' dimming with time. Any age trend would indicate that planets on wide orbits are transient relics of scattering from the inner disk. If planet detection rate is found to be independent of stellar age, it would confirm our prediction that gravitational instability is the dominant mode of producing detectable planets on wide orbits. We also predict that the occurrence ratio of long-period to short-period gas giants should be highest for M dwarfs due to the inefficiency of core accretion and the expected small fragment mass (∼10 M_Jup) in their disks.

Based on the data obtained from the Spitzer/Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIPMSE) Legacy Program and the Two Micron All Sky Survey (2MASS) project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8], and [8.0] μm, relative to the 2MASS K_s band (at 2.16 μm) for 131 GLIPMSE fields along the Galactic plane within |l| ⩽ 65^o, using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS K_s band), $A_{[3.6]}/A_{{K_{s}}}\approx 0.63\pm 0.01$, $A_{[4.5]}/A_{{K_{s}}}\approx 0.57\pm 0.03$, $A_{[5.8]}/A_{{K_{s}}}\approx 0.49\pm 0.03$, $A_{[8.0]}/A_{{K_{s}}}\approx 0.55\pm 0.03$, exhibits little variation with wavelength (i.e., the extinction is somewhat flat or gray). This is consistent with previous studies and agrees with that predicted from the standard interstellar grain model for R_V = 5.5 by Weingartner & Draine. As far as individual sightline is concerned, however, the wavelength dependence of the mid-infrared interstellar extinction $A_{\lambda }/A_{{K_{s}}}$ varies from one sightline to another, suggesting that there may not exist a "universal" IR extinction law. We, for the first time, demonstrate the existence of systematic variations of extinction with Galactic longitude which appears to correlate with the locations of spiral arms as well as with the variation of the far-infrared luminosity of interstellar dust.

We present the first results of a program to characterize the disk and envelope structure of typical Class 0 protostars in nearby low-mass star-forming regions. We use Spitzer Infrared Spectrograph (IRS) mid-infrared spectra, high-resolution Combined Array for Research in Millimeter-wave Astronomy (CARMA) 230 GHz continuum imaging, and two-dimensional radiative transfer models to constrain the envelope structure, as well as the size and mass of the circumprotostellar disk in Serpens FIRS 1. The primary envelope parameters (centrifugal radius, outer radius, outflow opening angle, and inclination) are well constrained by the spectral energy distribution (SED), including Spitzer IRAC and MIPS photometry, IRS spectra, and 1.1 mm Bolocam photometry. These together with the excellent uv-coverage (4.5–500 kλ) of multiple antenna configurations with CARMA allow for a robust separation of the envelope and a resolved disk. The SED of Serpens FIRS 1 is best fit by an envelope with the density profile of a rotating, collapsing spheroid with an inner (centrifugal) radius of approximately 600 AU, and the millimeter data by a large resolved disk with M_disk ∼ 1.0 M_☉ and R_disk ∼ 300 AU. These results suggest that large, massive disks can be present early in the main accretion phase. Results for the larger, unbiased sample of Class 0 sources in the Perseus, Serpens, and Ophiuchus molecular clouds are needed to determine if relatively massive disks are typical in the Class 0 stage.

We present the results of an Australia Telescope Compact Array 1.4 GHz spectropolarimetric aperture synthesis survey of 34 deg² centered on Centaurus A–NGC 5128. A catalog of 1005 extragalactic compact radio sources in the field to a continuum flux density of 3 mJy beam⁻¹ is provided along with a table of Faraday rotation measures (RMs) and linear polarized intensities for the 28% of sources with high signal to noise in linear polarization. We use the ensemble of 281 background polarized sources as line-of-sight probes of the structure of the giant radio lobes of Centaurus A. This is the first time such a method has been applied to radio galaxy lobes and we explain how it differs from the conventional methods that are often complicated by depth and beam depolarization effects. Assuming a magnetic field strength in the lobes of 1.3 B₁ μG, where B₁ = 1 is implied by equipartition between magnetic fields and relativistic particles, the upper limit we derive on the maximum possible difference between the average RM of 121 sources behind Centaurus A and the average RM of the 160 sources along sightlines outside Centaurus A implies an upper limit on the volume-averaged thermal plasma density in the giant radio lobes of 〈n_e〉 < 5 × 10⁻⁵B⁻¹₁ cm⁻³. We use an RM structure function analysis and report the detection of a turbulent RM signal, with rms σ_RM = 17 rad m⁻² and scale size 03, associated with the southern giant lobe. We cannot verify whether this signal arises from turbulent structure throughout the lobe or only in a thin skin (or sheath) around the edge, although we favor the latter. The RM signal is modeled as possibly arising from a thin skin with a thermal plasma density equivalent to the Centaurus intragroup medium density and a coherent magnetic field that reverses its sign on a spatial scale of 20 kpc. For a thermal density of n₁ 10⁻³ cm⁻³, the skin magnetic field strength is 0.8 n⁻¹₁ μG.

We present a coherent and homogeneous multi-line study of the CS molecule in nearby (D < 10 Mpc) galaxies. We include, from the literature, all the available observations from the J = 1–0 to the J = 7–6 transitions toward NGC 253, NGC 1068, IC 342, Henize 2-10, M 82, the Antennae Galaxies, and M 83. We have, for the first time, detected the CS(7–6) line in NGC 253, M 82 (both in the northeast and southwest molecular lobes), NGC 4038, M 83 and tentatively in NGC 1068, IC 342, and Henize 2-10. We use the CS molecule as a tracer of the densest gas component of the interstellar medium in extragalactic star-forming regions, following previous theoretical and observational studies by Bayet et al. In this first paper out of a series, we analyze the CS data sample under both local thermodynamical equilibrium (LTE) and non-LTE (large velocity gradient) approximations. We show that except for M 83 and Overlap (a shifted gas-rich position from the nucleus NGC 4039 in the Antennae Galaxies), the observations in NGC 253, IC 342, M 82-NE, M 82-SW, and NGC 4038 are not well reproduced by a single set of gas component properties and that, at least, two gas components are required. For each gas component, we provide estimates of the corresponding kinetic temperature, total CS column density, and gas density.

We present Spitzer observations of a sample of 12 starless cores selected to have prominent 24 μm shadows. The Spitzer images show 8 μm and 24 μm shadows and in some cases 70 μm shadows; these spatially resolved absorption features trace the densest regions of the cores. We have carried out a ¹²CO (2–1) and ¹³CO (2–1) mapping survey of these cores with the Heinrich Hertz Telescope (HHT). We use the shadow features to derive optical depth maps. We derive molecular masses for the cores and the surrounding environment; we find that the 24 μm shadow masses are always greater than or equal to the molecular masses derived in the same region, a discrepancy likely caused by CO freezeout onto dust grains. We combine this sample with two additional cores that we studied previously to bring the total sample to 14 cores. Using a simple Jeans mass criterion, we find that ∼2/3 of the cores selected to have prominent 24 μm shadows are collapsing or near collapse, a result that is supported by millimeter line observations. Of this subset at least half have indications of 70 μm shadows. All cores observed to produce absorption features at 70 μm are close to collapse. We conclude that 24 μm shadows, and even more so the 70 μm ones, are useful markers of cloud cores that are approaching collapse.

We present high-precision photometry of five consecutive transits of WASP-18, an extrasolar planetary system with one of the shortest orbital periods known. Through the use of telescope defocusing we achieve a photometric precision of 0.47–0.83 mmag per observation over complete transit events. The data are analyzed using the jktebop code and three different sets of stellar evolutionary models. We find the mass and radius of the planet to be M_b = 10.43 ±  0.30 ±  0.24 M_Jup and R_b = 1.165 ±  0.055 ±  0.014 R_Jup (statistical and systematic errors), respectively. The systematic errors in the orbital separation and the stellar and planetary masses, arising from the use of theoretical predictions, are of a similar size to the statistical errors and set a limit on our understanding of the WASP-18 system. We point out that seven of the nine known massive transiting planets (M_b > 3 M_Jup) have eccentric orbits, whereas significant orbital eccentricity has been detected for only four of the 46 less-massive planets. This may indicate that there are two different populations of transiting planets, but could also be explained by observational biases. Further radial velocity observations of low-mass planets will make it possible to choose between these two scenarios.

A detailed study of emission lines from Fe vii, Fe viii, and Fe ix observed by the EUV Imaging Spectrometer on board the Hinode satellite is presented. Spectra in the ranges 170–212 Å and 246–292 Å show strongly enhanced lines from the upper solar transition region (temperatures 5.4 ⩽ log T ⩽ 5.9) allowing a number of new line identifications to be made. Comparisons of Fe vii lines with predictions from a new atomic model reveal new plasma diagnostics, however there are a number of disagreements between theory and observation for emission line ratios insensitive to density and temperature, suggesting improved atomic data are required. Line ratios for Fe viii also show discrepancies with theory, with the strong λ185.21 and λ186.60 lines underestimated by 60%–80% compared to lines between 192 and 198 Å. A newly identified multiplet between 253.9 and 255.8 Å offers excellent temperature diagnostic opportunities relative to the lines between 185 and 198 Å, however the atomic model underestimates the strength of these lines by factors of 3–6. Two new line identifications are made for Fe ix at wavelengths 176.959 Å and 177.594 Å, while seven other lines between 186 and 200 Å are suggested to be due to Fe ix but for which transition identifications cannot be made. The new atomic data for Fe vii and Fe ix are demonstrated to significantly modify models for the response function of the Transition Region And Coronal Explorer 195 Å imaging channel, affecting temperature determinations from this channel. The data will also affect the response functions for other solar EUV imaging instruments such as SOHO/EIT, STEREO/EUVI, and the upcoming AIA instrument on the Solar Dynamics Observatory.

Astronomers have proposed a number of mechanisms to produce supernova explosions. Although many of these mechanisms are now not considered primary engines behind supernovae (SNe), they do produce transients that will be observed by upcoming ground-based surveys and NASA satellites. Here, we present the first radiation-hydrodynamics calculations of the spectra and light curves from three of these "failed" SNe: SNe with considerable fallback, accretion-induced collapse of white dwarfs, and energetic helium flashes (also known as type Ia SNe).

We have calculated the effects of large-scale solar flows, such as the meridional circulation, giant convection cells, and solar rotation on the helioseismic splitting coefficients using quasi-degenerate perturbation theory (QDPT). Our investigation reveals that the effect of poloidal flows like the large-scale meridional circulation are difficult to detect in observational data of the global acoustic modes since the frequency shifts are much less than the errors. However, signatures of large-scale convective flows may be detected if their amplitude is sufficiently large by looking for frequency shifts due to nearly degenerate modes coupled by convection. In this comprehensive study, we attempt to put limits on the magnitude of flow velocities in giant cells by comparing the splitting coefficients obtained from the QDPT treatment with observational data.

We construct and evolve three one-parameter families and one two-parameter family of steady-state models of stellar disks embedded in live dark matter (DM) halos in order to study the dynamical and secular phases of bar evolution. These models are tested against those published in the literature in order to extend them and to include the gaseous component in the follow-up paper. Specifically, we are interested in the angular momentum, J, redistribution in the disk–halo system during these two evolutionary phases without distinguishing between the resonant and non-resonant effects. We confirm the previous results and quantify for the first time the dual role that the DM halos play in the bar evolution: more centrally concentrated halos dilute the dynamical processes of the initial bar growth, such as the spontaneous bar instability and the vertical buckling instability, and slow down the J transfer, while facilitating it in the secular phase. The rate of J transfer in the disk and the halo is followed up in order to identify sites and times of peak activity in J emission and absorption. Within the corotation radius, R_cr, the disk J remains nearly constant in time, as long as R_cr stays within the disk—a sign that the lost angular momentum to the outer disk and the halo is being compensated by an influx of fresh J due to the outward motion of R_cr. We demonstrate that this is feasible as long as the bar slowdown dominates the loss of J inside R_cr. Next, we find that in some models the bar pattern speed stalls for prolonged time periods, i.e., the bar exhibits a constant rate of tumbling when R_cr is located outside the disk. This phenomenon appears concurrent with the near absence of J transfer between the disk and the halo, and is associated with the halo emittingJ at the corotation resonance and absorbing it at the inner Lindblad resonance. Furthermore, we confirm that stellar bars generally display the corotation-to-bar size ratios in the range of ∼1–1.4, but only between the times of the first buckling and R_cr leaving the disk. Hence, the corotation-to-disk size ratio emerges as an important dynamic discriminator between various stages of barred disk evolution. Finally, we analyze a number of correlations between the basic parameters of a barred disk and a halo, some already reported in the literature and some new.

The disk corona evaporation model extensively developed for the interpretation of observational features of black hole X-ray binaries (BHXRBs) is applied to active galactic nuclei (AGNs). Since the evaporation of gas in the disk can lead to its truncation for accretion rates less than a maximal evaporation rate, the model can naturally account for the soft spectrum in high-luminosity AGNs and the hard spectrum in low-luminosity AGNs. The existence of two different luminosity levels describing transitions from the soft to hard state and from the hard to soft state in BHXRBs, when applied to AGNs, suggests that AGNs can be in either spectral state within a range of luminosities. For example, at a viscosity parameter, α, equal to 0.3, the Eddington ratio from the hard-to-soft transition and from the soft-to-hard transition occurs at 0.027 and 0.005, respectively. The differing Eddington ratios result from the importance of Compton cooling in the latter transition, in which the cooling associated with soft photons emitted by the optically thick inner disk in the soft spectral state inhibits evaporation. When the Eddington ratio of the AGN lies below the critical value corresponding to its evolutionary state, the disk is truncated. With decreasing Eddington ratios, the inner edge of the disk increases to greater distances from the black hole with a concomitant increase in the inner radius of the broad-line region, R_BLR. The absence of an optically thick inner disk at low luminosities (L) gives rise to region in the R_BLR–L plane for which the relation R_BLR ∝ L^1/2 inferred at high luminosities is excluded. As a result, a lower limit to the accretion rate is predicted for the observability of broad emission lines, if the broad-line region is associated with an optically thick accretion disk. Thus, true Seyfert 2 galaxies may exist at very low accretion rates/luminosities. The differences between BHXRBs and AGNs in the framework of the disk corona model are discussed, and possible modifications to the model are briefly suggested.

We present direct evidence for dense clumps of matter in the companion wind in a Supergiant Fast X-ray Transient (SFXT) binary. This is seen as a brief period of enhanced absorption during one of the bright, fast flares that distinguish these systems. The object under study was IGR J17544−2619, and a total of 236 ks of data were accumulated with the Japanese satellite Suzaku. The activity in this period spans a dynamic range of almost 10⁴ in luminosity and gives a detailed look at SFXT behavior.

We point out a natural mechanism for quenching of star formation in early-type galaxies (ETGs). It automatically links the color of a galaxy with its morphology and does not require gas consumption, removal or termination of gas supply. Given that star formation takes place in gravitationally unstable gas disks, it can be quenched when a disk becomes stable against fragmentation to bound clumps. This can result from the growth of a stellar spheroid, for instance by mergers. We present the concept of morphological quenching (MQ) using standard disk instability analysis, and demonstrate its natural occurrence in a cosmological simulation using an efficient zoom-in technique. We show that the transition from a stellar disk to a spheroid can be sufficient to stabilize the gas disk, quench star formation, and turn an ETG red and dead while gas accretion continues. The turbulence necessary for disk stability can be stirred up by sheared perturbations within the disk in the absence of bound star-forming clumps. While other quenching mechanisms, such as gas stripping, active galactic nucleus feedback, virial shock heating, and gravitational heating are limited to massive halos, MQ can explain the appearance of red ETGs also in halos less massive than ∼10¹² M_☉. The dense gas disks observed in some of today's red ellipticals may be the relics of this mechanism, whereas red galaxies with quenched gas disks could be more frequent at high redshift.

Young stellar systems orbiting in the potential of their birth cluster can accrete from the dense molecular interstellar medium during the period between the star's birth and the dispersal of the cluster's gas. Over this time, which may span several Myr, the amount of material accreted can rival the amount in the initial protoplanetary disk; the potential importance of this "tail-end" accretion for planet formation was recently highlighted by Throop & Bally. While accretion onto a point mass is successfully modeled by the classical Bondi–Hoyle–Lyttleton solutions, the more complicated case of accretion onto a star–disk system defies analytic solution. In this paper, we investigate via direct hydrodynamic simulations the accretion of dense interstellar material onto a star with an associated gaseous protoplanetary disk. We discuss the changes to the structure of the accretion flow caused by the disk, and vice versa. We find that immersion in a dense accretion flow can redistribute disk material such that outer disk migrates inward, increasing the inner disk surface density and reducing the outer radius. The accretion flow also triggers the development of spiral density features, and changes to the disk inclination. The mean accretion rate onto the star remains roughly the same with and without the presence of a disk. We discuss the potential impact of this process on planet formation, including the possibility of triggered gravitational instability, inclination differences between the disk and the star, and the appearance of spiral structure in a gravitationally stable system.

We calculate and plot the synchrotron power, P_ν, the absorption coefficient, α_ν, and the source function, S_ν, for a power-law distribution of charged particles with Lorentz parameter values γ₁ ⩽ γ ⩽ γ₂. For this purpose, we define parametric functions Z_p(x, η), H_p(x, η), and Y_p(x, η) with η = γ₂/γ₁, such that P_ν ∝ Z_p(γ⁻²₁ν/ν₀, η), α_ν ∝ H_p(γ⁻²₁ν/ν₀, η), and S_ν ∝ Y_p(γ⁻²₁ν/ν₀, η). Corresponding asymptotic forms are also calculated and plotted for three frequency ranges, i.e., x ≪ 1, 1 ≪ x ≪ η², and x ≫ η², especially in the case of finite parameter η. Asymptotic forms of the middle range are possible for functions Z_p and Y_p for p>1/3, and for function H_p for all positive values of index p. A characteristic value, η_c(p, ε) (with ε ≪ 1), is then defined for each of the above functions so that for η ≳ η_c(p, ε) the middle range asymptotic forms could be considered. Further calculation details are also presented and discussed.

We have conducted a search for ionized gas at 3.6 cm, using the Very Large Array, toward 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 H ii regions are identified, of which 20 are newly discovered. Many of the H ii regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated toward the millimeter clumps; of the 31 millimeter clumps observed, nine of these appear to be physically related to ionized gas, and a further six have ionized gas emission within 1'. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7% ± 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power-law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.

We present new near-IR H₂, CO J = 2–1, and CO J = 3–2 observations to study outflows in the massive star-forming region IRAS 05358+3543. The Canada–France–Hawaii Telescope H₂ images and James Clerk Maxwell Telescope CO data cubes of the IRAS 05358 region reveal several new outflows, most of which emerge from the dense cluster of submillimeter cores associated with the Sh 2-233IR NE cluster to the northeast of IRAS 05358. We used Apache Point Observatory JHK spectra to determine line-of-sight velocities of the outflowing material. Analysis of archival Very Large Array cm continuum data and previously published very long baseline interferometry observations reveal a massive star binary as a probable source of one or two of the outflows. We have identified probable sources for six outflows and candidate counterflows for seven out of a total of 11 seen to be originating from the IRAS 05358 clusters. We classify the clumps within Sh 2-233IR NE as an early protocluster and Sh 2-233IR SW as a young cluster, and conclude that the outflow energy injection rate approximately matches the turbulent decay rate in Sh 2-233IR NE.

By systematically analyzing the Swift/XRT light curves detected before 2009 July, we find 19 light curves that monotonously decay as a single power law (SPL) with an index of 1 ∼ 1.7 from tens (or hundreds) of seconds to ∼10⁵ s post the gamma-ray burst (GRB) trigger. They are apparently different from the canonical light curves characterized by a shallow-to-normal decay transition. We compare the observations of the prompt gamma rays and the X-rays for these two samples of GRBs (SPL vs. canonical). No statistical difference is found in the prompt gamma-ray properties for the two samples. The X-ray properties of the two samples are also similar, although the SPL sample tends to have a slightly lower neutral hydrogen absorption column for the host galaxies and a slightly larger energy release compared with the canonical sample. The SPL X-ray Telescope (XRT) light curves in the burst frame gradually merge into a conflux, and their luminosities at 10⁵ s are normally distributed at log L/ergs s⁻¹ = 45.6 ± 0.5. The normal decay segment of the canonical XRT light curves has the same feature. Similar to the normal decay segment, the SPL light curves satisfy the closure relations and therefore can be roughly explained with external shock models. In the scenario that the X-rays are the afterglows of the GRB fireball, our results indicate that the shallow decay would be due to energy injection into the fireball and the total energy budget after injection for both samples of GRBs is comparable. More intriguing, we find that a prior X-ray emission model proposed by Yamazaki is more straightforward to interpret the observed XRT data. We show that the zero times (T₀) of the X-rays are 10²–10⁵ s prior to the GRB trigger for the canonical sample, and satisfy a log–normal distribution. The negligible T₀'s of the SPL sample are consistent with being the tail of T₀ distributions at low end, suggesting that the SPL sample and the canonical sample may be from a same parent sample. Referenced to T₀, the canonical XRT light curves well trace the SPL light curves. The T₀'s of the canonical light curves in our analysis are usually much larger than the offsets of the known precursors from the main GRBs. If the prior emission hypothesis is real, the X-ray emission is better interpreted within the external shock models based on the spectral and temporal indices of the X-rays. The lack of detection of a jet-like break in most XRT light curves implies that the opening angle of the prior emission jet would be usually large.

We generate simulations of the cosmic microwave background (CMB) temperature field as observed by the Wilkinson Microwave Anisotropy Probe (WMAP) satellite, taking into account the detailed shape of the asymmetric beams and scanning strategy of the experiment, and use these to re-estimate the WMAP beam transfer functions. This method avoids the need of artificially symmetrizing the beams, as done in the baseline WMAP approach, and instead measures the total convolution effect by direct simulation. We find only small differences with respect to the nominal transfer functions, typically less than 1% everywhere, and less than 0.5% at ℓ < 400. The net effect on the CMB power spectrum is less than 0.6%. The effect on all considered cosmological parameters is negligible. For instance, we find that the spectral index of scalar perturbations after taking into account the beam asymmetries is n_s = 0.964 ± 0.014, corresponding to a negative shift of −0.1σ compared to the previously released WMAP results. Our CMB sky simulations are made publicly available and can be used for general studies of asymmetric beam effects in the WMAP data.

A large amount of observations have constrained cosmological parameters and the initial density fluctuation spectrum to a very high accuracy. However, cosmological parameters change with time and the power index of the power spectrum dramatically varies with mass scale in the so-called concordance ΛCDM cosmology. Thus, any successful model for its structural evolution should work well simultaneously for various cosmological models and different power spectra. We use a large set of high-resolution N-body simulations of a variety of structure formation models (scale-free, standard CDM, open CDM, and ΛCDM) to study the mass accretion histories, the mass and redshift dependence of concentrations, and the concentration evolution histories of dark matter halos. We find that there is significant disagreement between the much-used empirical models in the literature and our simulations. Based on our simulation results, we find that the mass accretion rate of a halo is tightly correlated with a simple function of its mass, the redshift, parameters of the cosmology, and of the initial density fluctuation spectrum, which correctly disentangles the effects of all these factors and halo environments. We also find that the concentration of a halo is strongly correlated with the universe age when its progenitor on the mass accretion history first reaches 4% of its current mass. According to these correlations, we develop new empirical models for both the mass accretion histories and the concentration evolution histories of dark matter halos, and the latter can also be used to predict the mass and redshift dependence of halo concentrations. These models are accurate and universal: the same set of model parameters works well for different cosmological models and for halos of different masses at different redshifts, and in the ΛCDM case the model predictions match the simulation results very well even though halo mass is traced to about 0.0005 times the final mass, when cosmological parameters and the power index of the initial density fluctuation spectrum have changed dramatically. Our model predictions also match the PINOCCHIO mass accretion histories very well, which are much independent of our numerical simulations and our definitions of halo merger trees. These models are also simple and easy to implement, making them very useful in modeling the growth and structure of dark matter halos. We provide appendices describing the step-by-step implementation of our models. A calculator which allows one to interactively generate data for any given cosmological model is provided on the Web, together with a user-friendly code to make the relevant calculations and some tables listing the expected concentration as a function of halo mass and redshift in several popular cosmological models. We explain why ΛCDM and open CDM halos on nearly all mass scales show two distinct phases in their mass growth histories. We discuss implications of the universal relations we find in connection to the formation of dark matter halos in the cosmic density field.

We study the survival of ultrahigh energy nuclei injected in clusters of galaxies, as well as their secondary neutrino and photon emissions, using a complete numerical propagation method and a realistic modeling of the magnetic, baryonic, and photonic backgrounds. It is found that the survival of heavy nuclei highly depends on the injection position and on the profile of the magnetic field. Taking into account the limited lifetime of the central source could also lead in some cases to the detection of a cosmic-ray afterglow, temporally decorrelated from neutrino and gamma-ray emissions. We calculate that the diffusive neutrino flux around 1 PeV coming from clusters of galaxies may have a chance to be detected by current instruments. The observation of single sources in neutrinos and in gamma rays produced by ultrahigh energy cosmic rays will be more difficult. Signals coming from lower energy cosmic rays (E ≲ 1 PeV), if they exist, might however be detected by Fermi, for reasonable sets of parameters.

The measurement of redshifts for gamma-ray bursts (GRBs) is an important issue for the study of the high redshift universe and cosmology. We are constructing a program to estimate the redshifts for GRBs from the original Swift light curves and spectra, aiming to get redshifts for the Swift bursts without spectroscopic or photometric redshifts. We derive the luminosity indicators from the light curves and spectra of each burst, including the lag time between low and high photon energy light curves, the variability of the light curve, the peak energy of the spectrum, the number of peaks in the light curve, and the minimum rise time of the peaks. These luminosity indicators can each be related directly to the luminosity, and we combine their independent luminosities into one weighted average. Then with our combined luminosity value, the observed burst peak brightness, and the concordance redshift–distance relation, we can derive the redshift for each burst. In this paper, we test the accuracy of our method on 107 bursts with known spectroscopic redshift. The reduced χ² of our best redshifts (z_best) compared with known spectroscopic redshifts (z_spec) is 0.86, and the average value of log₁₀(z_best/z_spec) is 0.01, with this indicating that our error bars are good and our estimates are not biased. The rms scatter of log₁₀(z_best/z_spec) is 0.26, with a comparison of 0.30 for rms of log₁₀(z_spec). We made a selection on bursts with relatively accurate redshift estimation. The rms of log(z_best/z_spec) decreases to 0.19, and the rms scatter of log₁₀(z_spec)for this subsample is 0.28. For Swift bursts measured over a relatively narrow energy band, the uncertainty in determining the peak energy is one of the main restrictions on our accuracy. Although the accuracy of our z_best values are not as good as that of spectroscopic redshifts, it is very useful for demographic studies, as our sample is nearly complete and the redshifts do not have the severe selection effects associated with optical spectroscopy.

We study the heating of charged test particles in three-dimensional numerical simulations of weakly compressible magnetohydrodynamic (MHD) turbulence ("Alfvénic turbulence"); we focus on plasmas with comparable thermal and magnetic energy densities, i.e., β ∼ 0.1–10. Our results are relevant to particle heating and acceleration in the solar wind, accretion disks onto black holes, and other astrophysics and heliospheric environments. The physics of particle heating depends on whether the gyrofrequency of a particle Ω₀ is comparable to the frequency of a turbulent fluctuation ω that is resolved on the computational domain. Particles with Ω₀ ∼ ω undergo strong perpendicular heating (relative to the local magnetic field) and pitch angle scattering. By contrast, particles with Ω₀ ≫ ω undergo strong parallel heating. Simulations with a finite resistivity produce additional parallel heating due to parallel electric fields in small-scale current sheets. Many of our results are consistent with linear theory predictions for the particle heating produced by the Alfvén and slow magnetosonic waves that make up Alfvénic turbulence. However, in contrast to linear theory predictions, energy exchange is not dominated by discrete resonances between particles and waves; instead, the resonances are substantially "broadened." We discuss the implications of our results for solar and astrophysics problems, in particular, the thermodynamics of the near-Earth solar wind. This requires an extrapolation of our results to higher numerical resolution, because the dynamic range that can be simulated is far less than the true dynamic range between the proton cyclotron frequency and the outer-scale frequency of MHD turbulence. We conclude that Alfvénic turbulence produces significant parallel heating via the interaction between particles and magnetic field compressions ("slow waves"). However, on scales above the proton Larmor radius Alfvénic turbulence does not produce significant perpendicular heating of protons or minor ions (this is consistent with linear theory, but inconsistent with previous claims from test particle simulations). Instead, the Alfvén wave energy cascades to perpendicular scales below the proton Larmor radius, initiating a kinetic Alfvén wave cascade.

Three-dimensional instability of the spontaneous fast magnetic reconnection is studied with magnetohydrodynamics (MHD) simulation, where the two-dimensional model of the spontaneous fast magnetic reconnection is destabilized in three dimensions. In two-dimensional models, every plasma condition is assumed to be uniform in the sheet current direction. In that case, it is well known that the two-dimensional fast magnetic reconnection can be caused by current-driven anomalous resistivity, when an initial resistive disturbance is locally put in a one-dimensional current sheet. In this paper, it is studied whether the two-dimensional fast magnetic reconnection can be destabilized or not when the initial resistive disturbance is three dimensional, i.e., that which has weak fluctuations in the sheet current direction. According to our study, the two-dimensional fast magnetic reconnection is developed to the three-dimensional intermittent fast magnetic reconnection which is strongly localized in the sheet current direction. The resulting fast magnetic reconnection repeats to randomly eject three-dimensional magnetic loops which are very similar to the intermittent downflows observed in solar flares. In fact, in some observations of solar flares, the current sheet seems to be approximately one dimensional, but the fast magnetic reconnection is strongly localized in the sheet current direction, i.e., fully three dimensional. In addition, the observed plasma downflows as snake-like curves. It is shown that those observed features are consistent with our numerical MHD study.

We report on a global, three-dimensional GRMHD simulation of an accretion torus embedded in a large-scale vertical magnetic field orbiting a Schwarzschild black hole. This simulation investigates how a large-scale vertical field evolves within a turbulent accretion disk and whether global magnetic field configurations suitable for launching jets and winds can develop. We find that a "coronal mechanism" of magnetic flux motion, which operates largely outside the disk body, dominates global flux evolution. In this mechanism, magnetic stresses driven by orbital shear create large-scale half-loops of magnetic field that stretch radially inward and then reconnect, leading to discontinuous jumps in the location of magnetic flux. In contrast, little or no flux is brought in directly by accretion within the disk itself. The coronal mechanism establishes a dipole magnetic field in the evacuated funnel around the orbital axis with a field intensity regulated by a combination of the magnetic and gas pressures in the inner disk. These results prompt a re-evaluation of previous descriptions of magnetic flux motion associated with accretion. Local pictures are undercut by the intrinsically global character of magnetic flux. Formulations in terms of an "effective viscosity" competing with an "effective resistivity" are undermined by the nonlinearity of the magnetic dynamics and the fact that the same turbulence driving mass motion (traditionally identified as "viscosity") can alter magnetic topology.

We report on the discovery of a planetary system with a close-in transiting hot Jupiter on a near circular orbit and a massive outer planet on a highly eccentric orbit. The inner planet, HAT-P-13b, transits the bright V = 10.622 G4 dwarf star GSC 3416 − 00543 every P = 2.916260 ± 0.000010 days, with transit epoch T_c = 2454779.92979 ± 0.00038 (BJD) and duration 0.1345 ± 0.0017 days. The outer planet HAT-P-13c orbits the star every P₂ = 428.5 ± 3.0 days with a nominal transit center (assuming zero impact parameter) of T_2c = 2454870.4 ± 1.8 (BJD) or time of periastron passage T_2,peri = 2454890.05 ± 0.48 (BJD). Transits of the outer planet have not been observed, and may not be present. The host star has a mass of 1.22^+0.05_−0.10M_☉, radius of 1.56 ± 0.08 R_☉, effective temperature of 5653 ± 90 K, and is rather metal-rich with [Fe/H] = +0.41 ± 0.08. The inner planetary companion has a mass of 0.853^+0.029_−0.046 M_J, and radius of 1.281 ± 0.079 R_J, yielding a mean density of 0.498^+0.103_−0.069 g cm⁻³. The outer companion has m₂sin i₂ = 15.2 ± 1.0 M_J, and orbits on a highly eccentric orbit of e₂ = 0.691 ± 0.018. While we have not detected significant transit timing variations of HAT-P-13b, due to gravitational and light-travel time effects, future observations will constrain the orbital inclination of HAT-P-13c, along with its mutual inclination to HAT-P-13b. The HAT-P-13 (b, c) double-planet system may prove extremely valuable for theoretical studies of the formation and dynamics of planetary systems.

Positronium is a short-lived atom consisting of a bound electron–positron pair. In the triplet state, when the spins of both particles are parallel, radiative recombination lines will be emitted prior to annihilation. The existence of celestial positronium is revealed through gamma-ray observations of its annihilation products. These observations, however, have intrinsically low angular resolution. In this paper, we examine the prospects for detecting the positronium recombination spectrum. Such observations have the potential to reveal discrete sources of e⁺ for the first time and will allow the acuity of optical telescopes and instrumentation to be applied to observations of high-energy phenomena. We review the theory of the positronium recombination spectrum and provide formulae to calculate expected line strengths from the e⁺ production rate and for different conditions in the interstellar medium. We estimate the positronium emission line strengths for several classes of Galactic and extragalactic sources. These are compared to current observational limits and to current and future sensitivities of optical and infrared instrumentation. We find that observations of the Psα line should soon be possible due to recent advances in NIR spectroscopy.

We use a high-resolution N-body simulation to investigate the influence of background galaxy properties, including redshift, size, shape, and clustering, on the efficiency of forming giant arcs by gravitational lensing of rich galaxy clusters. Two large sets of ray-tracing simulations are carried out for 10 massive clusters at two redshifts, i.e., z_l ∼ 0.2 and 0.3. The virial mass (M_vir) of the simulated lens clusters at z ∼ 0.2 ranges from 6.8 × 10¹⁴ h⁻¹ M_☉ to 1.1 × 10¹⁵ h⁻¹ M_☉. The information of background galaxies brighter than 25 mag in the I-band is taken from the Cosmological Evolution Survey (COSMOS) imaging data. Around 1.7 × 10⁵ strong lensing realizations with these images as background galaxies have been performed for each set. We find that the efficiency for forming giant arcs for z_l = 0.2 clusters is broadly consistent with observations. Our study on control source samples shows that the number of giant arcs is decreased by a factor of 1.05 and 1.61 when the COSMOS redshift distribution of galaxies is adopted, compared to the cases where all the galaxies were assumed to be in a single source plane at z_l = 1.0 and z_l = 1.5, respectively. We find that the efficiency of producing giant arcs by rich clusters is weakly dependent on the source size and clustering. Our principal finding is that a small proportion (∼1/3) of galaxies with elongated shapes (e.g., ellipticity = 1 − b/a > 0.5) can boost the number of giant arcs substantially. Compared with recent studies where a uniform ellipticity distribution from 0 to 0.5 is used for the sources, the adoption of directly observed shape distribution increases the number of giant arcs by a factor of ∼2. Our results indicate that it is necessary to account for source information and survey parameters (such as point-spread function, seeing) to make correct predictions of giant arcs and further to constrain the cosmological parameters.

Semiempirical atmospheric models of solar surface features as observed at moderate resolution are useful tools for understanding the observed solar spectral irradiance variations. Paper I described a set of models constructed to reproduce the observed radiance spectrum for solar surface features at ∼2 arcsec resolution that constitute an average over small-scale features such as granulation. Paper II showed that a revision of previous models of low-chromospheric inter-network regions explains the observed infrared CO lines in addition to the UV and radio continuum from submillimeter to centimetric wavelengths. The present paper (1) shows that the Ca ii H and K line wing observations are also explained by the new quiet-Sun-composite model, (2) introduces new low-chromospheric models of magnetic features that follow the ideas in Paper II, (3) introduces new upper chromospheric structures for all quiet-Sun and active-region models, and (4) shows how the new set of models explains EUV/FUV observations of spectral radiance and irradiance. This paper also discusses the chromospheric radiative-loss estimates in each of the magnetic features. The new set of models provides a basis for the spectral irradiance synthesis at EUV/FUV wavelengths based on the features observed on the solar surface.

On 2007 December 7, there was an eruption from AR 10977, which also hosted a sigmoid. An EUV Imaging Telescope (EIT) wave associated with this eruption was observed by EUVI on board the Solar Terrestrial Relations Observatory (STEREO). Using EUVI images in the 171 Å and the 195 Å passbands from both STEREO A and B, we study the morphology and kinematics of this EIT wave. In the early stages, images of the EIT wave from the two STEREO spacecrafts differ markedly. We determine that the EUV fronts observed at the very beginning of the eruption likely include some intensity contribution from the associated coronal mass ejection (CME). Additionally, our velocity measurements suggest that the EIT wave front may propagate at nearly constant velocity. Both results offer constraints on current models and understanding of EIT waves.

We combine near-infrared (Two Micron All Sky Survey) and mid-infrared (Spitzer-IRAC) photometry to characterize the IR extinction law (1.2–8 μm) over nearly 150° of contiguous Milky Way midplane longitude. The relative extinctions in five passbands across these wavelength and longitude ranges are derived by calculating color excess ratios for G and K giant red clump stars in contiguous midplane regions and deriving the wavelength dependence of extinction in each one. Strong, monotonic variations in the extinction law shape are found as a function of angle from the Galactic center, symmetric on either side of it. These longitudinal variations persist even when dense interstellar regions, known a priori to have a shallower extinction curve, are removed. The increasingly steep extinction curves toward the outer Galaxy indicate a steady decrease in the absolute-to-selective extinction ratio (R_V) and in the mean dust grain size at greater Galactocentric angles. We note an increasing strength of the 8 μm extinction inflection at high Galactocentric angles and, using theoretical dust models, show that this behavior is consistent with the trend in R_V. Along several lines of sight where the solution is most feasible, A_λ/A_Ks as a function of Galactic radius (R_GC) is estimated and shown to have a Galactic radial dependence. Our analyses suggest that the observed relationship between extinction curve shape and Galactic longitude is due to an intrinsic dependence of the extinction law on Galactocentric radius.

We study the line profiles of a range of transition region (TR) emission lines observed in typical quiet-Sun regions. In magnetic network regions, the Si iv 1402 Å, C iv 1548 Å, N v 1238 Å, O vi 1031 Å, and Ne viii 770 Å spectral lines show significant asymmetry in the blue wing of the emission line profiles. We interpret these high-velocity upflows in the lower and upper TR as the quiet-Sun equivalent of the recently discovered upflows in the low corona above plage regions. The latter have been shown to be directly associated with high-velocity chromospheric spicules that are (partially) heated to coronal temperatures and play a significant role in supplying the active region corona with hot plasma. We show that a similar process likely dominates the quiet-Sun network. We provide a new interpretation of the observed quiet-Sun TR emission in terms of the relentless mass transport between the chromosphere and corona—a mixture of emission from dynamic episodic heating and mass injection into the corona as well as that from the previously filled, slowly cooling, coronal plasma. Analysis of the observed upflow component shows that it carries enough hot plasma to play a significant role in the energy and mass balance of the quiet corona. We determine the temperature dependence of the upflow velocities to constrain the acceleration and heating mechanism that drives these upflows. We also show that the temporal characteristics of these upflows suggest an episodic driver that sometimes leads to quasi-periodic signals. We suggest that at least some of the quasi-periodicities observed with coronal imagers and spectrographs that have previously been interpreted as propagating magnetoacoustic waves, may instead be caused by these upflows.

The turbulence effects on the charge capture process are investigated in weak turbulent plasmas. The effective interaction potential taking into account the correction factor to the nonlinear dielectric function due to the fluctuation of the electric fields and Bohr–Lindhard model are employed in order to obtain the electron capture radius and electron capture cross section in turbulent plasmas. It is shown that the influence of the fluctuating electric fields in the plasma considerably decreases the electron charge capture radius and electron capture probability. Hence, we have found that the turbulence effect strongly suppresses the electron capture cross section in weak turbulent plasmas. In addition, it is found that the electron capture radius and electron cross section decrease with an increase of the projectile energy.

We present a new "collisional grooming" algorithm that enables us to model images of debris disks where the collision time is less than the Poynting–Robertson (PR) time for the dominant grain size. Our algorithm uses the output of a collisionless disk simulation to iteratively solve the mass flux equation for the density distribution of a collisional disk containing planets in three dimensions. The algorithm can be run on a single processor in ∼1 hr. Our preliminary models of disks with resonant ring structures caused by terrestrial mass planets show that the collision rate for background particles in a ring structure is enhanced by a factor of a few compared to the rest of the disk, and that dust grains in or near resonance have even higher collision rates. We show how collisions can alter the morphology of a resonant ring structure by reducing the sharpness of a resonant ring's inner edge and by smearing out azimuthal structure. We implement a simple prescription for particle fragmentation and show how PR drag and fragmentation sort particles by size, producing smaller dust grains at smaller circumstellar distances. This mechanism could cause a disk to look different at different wavelengths, and may explain the warm component of dust interior to Fomalhaut's outer dust ring seen in the resolved 24 μm Spitzer image of this system.

We perform halo occupation distribution (HOD) modeling to interpret small-scale and intermediate-scale clustering of 35,000 luminous early-type galaxies and their cross-correlation with a reference imaging sample of normal L_* galaxies in the Sloan Digital Sky Survey. The modeling results show that most of these luminous red galaxies (LRGs) are central galaxies residing in massive halos of typical mass M∼ a few times 10¹³–10¹⁴h⁻¹M_☉, while a few percent of them have to be satellites within halos in order to produce the strong auto-correlations exhibited on smaller scales. The mean luminosity L_c of central LRGs increases with the host halo mass, with a rough scaling relation of L_c ∝ M^0.5. The halo mass required to host on average one satellite LRG above a luminosity threshold is found to be about 10 times higher than that required to host a central LRG above the same threshold. We find that in massive halos the distribution of L_* galaxies roughly follows that of the dark matter and their mean occupation number scales with halo mass as M^1.5. The HOD modeling results also allow for an intuitive understanding of the scale-dependent luminosity dependence of the cross-correlation between LRGs and L_* galaxies. Constraints on the LRG HOD provide tests for models of formation and evolution of massive galaxies, and they are also useful for cosmological parameter investigations. In one of the appendices, we provide LRG HOD parameters with dependence on cosmology inferred from modeling the two-point auto-correlation functions of LRGs.

Approximately 30% of luminous red giants exhibit a long secondary period (LSP) of variation in their light curves in addition to a shorter primary period of oscillation. The cause of the LSP has so far defied explanation: leading possibilities are binarity and a nonradial mode of oscillation. Here, large samples of red giants in the Large Magellanic Cloud both with and without LSPs are examined for evidence of an 8 or 24 μm mid-IR excess caused by circumstellar dust. It is found that stars with LSPs show a significant mid-IR excess compared to stars without LSPs. Furthermore, the near-IR J − K color seems unaffected by the presence of the 24 μm excess. These findings indicate that LSPs cause mass ejection from red giants and that the lost mass and circumstellar dust is most likely in either a clumpy or a disk-like configuration. The underlying cause of the LSP and the mass ejection remains unknown.

The Fermi Gamma-ray Space Telescope has opened a new high-energy window in the study of gamma-ray bursts (GRBs). Here we present a thorough analysis of GRB 080825C, which triggered the Fermi Gamma-ray Burst Monitor (GBM), and was the first firm detection of a GRB by the Fermi Large Area Telescope (LAT). We discuss the LAT event selections, background estimation, significance calculations, and localization for Fermi GRBs in general and GRB 080825C in particular. We show the results of temporal and time-resolved spectral analysis of the GBM and LAT data. We also present some theoretical interpretation of GRB 080825C observations as well as some common features observed in other LAT GRBs.

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic-Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to ∼10¹⁴ eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an E^{−2.66 ± 0.04} power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100–800 GeV/n energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be 0.080 ± 0.025 (stat.)±0.025 (sys.) at ∼800 GeV/n, in good agreement with a recent result from the first CREAM flight.

To explore the possible causes of the observed asymmetric helicity flux in emerging active regions between the leading and following polarities reported in a recent study by Tian & Alexander, we examine the subsurface evolution of buoyantly rising Ω-shaped flux tubes using three-dimensional, spherical-shell anelastic MHD simulations. We find that due to the asymmetric stretching of the Ω-shaped tube by the Coriolis force, the leading side of the emerging tube has a greater field strength, is more buoyant, and remains more cohesive compared to the following side. As a result, the magnetic field lines in the leading leg show more coherent values of local twist α ≡ (∇ × B) · B/B², whereas the values in the following leg show large fluctuations and are of mixed sign. On average, however, the field lines in the leading leg do not show a systematically greater mean twist compared to the following leg. Due to the higher rise velocity of the leading leg, the upward helicity flux through a horizontal cross section at each depth in the upper half of the convection zone is significantly greater in the leading polarity region than that in the following leg. This may contribute to the observed asymmetric helicity flux in emerging active regions. Furthermore, based on a simplified model of active region flux emergence into the corona by Longcope & Welsch, we show that a stronger field strength in the leading tube can result in a faster rotation of the leading polarity sunspot driven by torsional Alfvén waves during flux emergence into the corona, contributing to a greater helicity injection rate in the leading polarity of an emerging active region.

We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z = 0.102) during a strong outburst of very high energy gamma-ray emission in 2008 June. The very high energy gamma-ray signal was detected by VERITAS on 2008 June 7–8 with a flux F(>200 GeV) =(5.7 ± 0.6) × 10⁻¹¹ cm⁻² s⁻¹, about three times brighter than during the discovery of gamma-ray emission from W Com by VERITAS in 2008 March. The initial detection of this flare by VERITAS at energies above 200 GeV was followed by observations in high-energy gamma rays (AGILE; E_γ⩾ 100 MeV), X-rays (Swift and XMM-Newton), and at UV, and ground-based optical and radio monitoring through the GASP–WEBT consortium and other observatories. Here we describe the multiwavelength data and derive the spectral energy distribution of the source from contemporaneous data taken throughout the flare.

Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

We present infrared interferometric imaging of the S-type Mira star χ Cygni. The object was observed at four different epochs in 2005–2006 with the Infrared-Optical Telescope Array optical interferometer (H band). Images show up to 40% variation in the stellar diameter, as well as significant changes in the limb darkening and stellar inhomogeneities. Model fitting gave precise time-dependent values of the stellar diameter, and reveals presence and displacement of a warm molecular layer. The star radius, corrected for limb darkening, has a mean value of 12.1 mas and shows a 5.1 mas amplitude pulsation. Minimum diameter was observed at phase 0.94 ± 0.01. Maximum temperature was observed several days later at phase 1.02 ± 0.02. We also show that combining the angular acceleration of the molecular layer with CO (Δv = 3) radial velocity measurements yields a 5.9 ± 1.5 mas parallax. The constant acceleration of the CO molecules—during 80% of the pulsation cycle—lead us to argument for a free-falling layer. The acceleration is compatible with a gravitational field produced by a 2.1^+1.5_−0.7 solar mass star. This last value is in agreement with fundamental mode pulsator models. We foresee increased development of techniques consisting in combining radial velocity with interferometric angular measurements, ultimately allowing total mapping of the speed, density, and position of the diverse species in pulsation-driven atmospheres.

We used Suzaku observations of the molecular cloud MBM20 and a low neutral hydrogen column density region nearby to separate and characterize the foreground and background diffuse X-ray emission. A comparison with a previous observation of the same regions with XMM-Newton indicates a significant change in the foreground flux which is attributed to Solar Wind Charge eXchange (SWCX). The data have also been compared with previous results from similar "shadow" experiments and with a SWCX model to characterize its O vii and O viii emission.

V893 Sco is an eclipsing dwarf nova that had attracted little attention from X-ray astronomers until it was proposed as the identification of an Rossi X-Ray Timing Explorer all-sky slew survey (XSS) source. Here, we report on the pointed X-ray observations of this object using Suzaku. V893 Sco was in quiescence at the time, as indicated by the coordinated optical photometry we obtained at the South African Astronomical Observatory. Our Suzaku data show V893 Sco to be X-ray bright, with a highly absorbed spectrum. Most importantly, we have discovered a partial X-ray eclipse in V893 Sco. This is the first time that a partial eclipse is seen in X-ray light curves of a dwarf nova. Our preliminary simulations demonstrate that the partial X-ray eclipse can be in principle reproduced if the white dwarf in V893 Sco is partially eclipsed. Higher quality observations of this object have the potential to place significant constraints on the latitudinal extent of the X-ray emission region and thereby discriminating between an equatorial boundary layer and a spherical corona. The partial X-ray eclipse therefore makes V893 Sco a key object in understanding the physics of accretion in quiescent dwarf nova.

Transverse oscillations of solar filament and prominence threads have been frequently reported. These oscillations have the common features of being of short period (2–10 minutes) and being damped after a few periods. The observations are interpreted as kink magnetohydrodynamic (MHD) wave modes, whereas resonant absorption in the Alfvén continuum and ion-neutral collisions are candidates to be the damping mechanisms. Here, we study both analytically and numerically the time damping of kink MHD waves in a cylindrical, partially ionized filament thread embedded in a coronal environment. The thread model is composed of a straight and thin, homogeneous filament plasma, with a transverse inhomogeneous transitional layer where the plasma physical properties vary continuously from filament to coronal conditions. The magnetic field is homogeneous and parallel to the thread axis. We find that the kink mode is efficiently damped by resonant absorption for typical wavelengths of filament oscillations, the damping times being compatible with the observations. Partial ionization does not affect the process of resonant absorption, and the filament plasma ionization degree is only important for the damping for wavelengths much shorter than those observed. To our knowledge, this is the first time that the phenomenon of resonant absorption is studied in a partially ionized plasma.

We report extensive spectroscopic and differential photometric BVRI observations of the active, detached, 1.309-day double-lined eclipsing binary IM Vir, composed of a G7-type primary and a K7 secondary. With these observations, we derive accurate absolute masses and radii of M₁ = 0.981 ± 0.012 M_☉, M₂ = 0.6644 ± 0.0048 M_☉, R₁ = 1.061 ± 0.016 R_☉, and R₂ = 0.681 ± 0.013 R_☉ for the primary and secondary, with relative errors under 2%. The effective temperatures are 5570 ± 100 K and 4250 ± 130 K, respectively. The significant difference in mass makes this a favorable case for comparison with stellar evolution theory. We find that both stars are larger than the models predict, by 3.7% for the primary and 7.5% for the secondary, as well as cooler than expected, by 100 K and 150 K, respectively. These discrepancies are in line with previously reported differences in low-mass stars, and are believed to be caused by chromospheric activity, which is not accounted for in current models. The effect is not confined to low-mass stars: the rapidly rotating primary of IM Vir joins the growing list of objects of near-solar mass (but still with convective envelopes) that show similar anomalies. The comparison with the models suggests an age of 2.4 Gyr for the system, and a metallicity of [Fe/H] ≈−0.3 that is consistent with other indications, but requires confirmation.

We report the discovery of four very bright, strongly lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed up with spectroscopy and imaging data from the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory and found to have redshift z > 2.0. With isophotal magnitudes r = 19.2–20.4 and 3'' diameter magnitudes r = 20.0–20.6, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 50 to 127, and use those to derive the enclosed masses of the lensing galaxies.

We quantify the rapid variations in X-ray brightness ("flares") from the extremely massive colliding wind binary η Carinae seen during the past three orbital cycles by the Rossi X-ray Timing Explorer. The observed flares tend to be shorter in duration and more frequent as periastron is approached, although the largest ones tend to be roughly constant in strength at all phases. Plausible scenarios include (1) the largest of multi-scale stochastic wind clumps from the Luminous Blue Variable (LBV) component entering and compressing the hard X-ray-emitting wind–wind collision (WWC) zone, (2) large-scale corotating interacting regions in the LBV wind sweeping across the WWC zone, or (3) instabilities intrinsic to the WWC zone. The first one appears to be the most consistent with the observations, requiring homologously expanding clumps as they propagate outward in the LBV wind and a turbulence-like power-law distribution of clumps, decreasing in number toward larger sizes, as seen in Wolf–Rayet winds.

We present IRAC/MIPS Spitzer observations of intermediate-mass stars in the 5 Myr old λ Orionis cluster. In a representative sample of stars earlier than F5 (29 stars), we find a population of nine stars with varying degree of moderate 24 μm excess comparable to those produced by debris disks in older stellar groups. As expected in debris disks systems, those stars do not exhibit emission lines in their optical spectra. We also include in our study the star HD 245185, a known Herbig Ae object which displays excesses in all Spitzer bands and shows emission lines in its spectrum. We compare the disk population in the λ Orionis cluster with the disk census in other stellar groups studied using similar methods to detect and characterize their disks and spanning a range of ages from 3 Myr to 10 Myr. We find that for stellar groups of 5 Myr or older the observed disk frequency in intermediate-mass stars (with spectral types from late B to early F) is higher than in low-mass stars (with spectral types K and M). This is in contradiction with the observed trend for primordial disk evolution, in which stars with higher stellar masses dissipate their primordial disks faster. At 3 Myr, the observed disk frequency in intermediate-mass stars is still lower than for low-mass stars indicating that second generation dusty disks start to dominate the disk population at 5 Myr for intermediate-mass stars. This result agrees with recent models of evolution of solids in the region of the disk where icy objects form (>30 AU), which suggest that at 5–10 Myr collisions start to produce large amount of dust during the transition from runaway to oligarchic growth (reaching sizes of ∼500 km) and then dust production peaks at 10–30 Myr, when objects reach their maximum size (⩾1000 km).

While there have been multiple observational programs aimed at detecting linear polarization of optical radiation emitted by ultracool dwarfs, there has been comparatively less rigorous theoretical analysis of the problem. The general expectation has been that the atmospheres of those substellar-mass objects with condensate clouds would give rise to linear polarization due to scattering. Because of rotation-induced non-sphericity, there is expected to be incomplete cancellation of disk-integrated net polarization and thus a finite polarization. For cloudless objects, however, only molecular Rayleigh scattering will contribute to any net polarization and this limit has not been well studied. Hence in this paper we present a detailed multiple scattering analysis of the polarization expected from those T-dwarfs whose spectra show absence of condensates. For this, we develop and solve the full radiative transfer equations for linearly polarized radiation. Only atomic and molecular Rayleigh scattering are considered to be the sources of polarization. We compute the local polarization at different angular directions in a plane-parallel atmosphere calculated for the range of effective temperatures of T dwarfs and then average over the whole surface of the object. The effects of gravity and limb darkening as well as rotation induced non-sphericity are included. It is found that the amount of polarization decreases with the increase in effective temperature. It is also found that significant polarization at any local point in the atmosphere arises only in the optical (B band). However, the disk integrated polarization—even in the B band—is negligible. Hence we conclude that, unlike the case for cloudy L dwarfs, polarization of cloudless T dwarfs by atomic and molecular scattering may not be detectable. In the future we will extend this work to cloudy L and T dwarf atmospheres.

Following the recent discovery of γ rays from the radio-loud narrow-line Seyfert 1 galaxy PMN J0948+0022 (z = 0.5846), we started a multiwavelength campaign from radio to γ rays, which was carried out between the end of 2009 March and the beginning of July. The source displayed activity at all the observed wavelengths: a general decreasing trend from optical to γ-ray frequencies was followed by an increase of radio emission after less than two months from the peak of the γ-ray emission. The largest flux change, about a factor of about 4, occurred in the X-ray band. The smallest was at ultraviolet and near-infrared frequencies, where the rate of the detected photons dropped by a factor 1.6–1.9. At optical wavelengths, where the sampling rate was the highest, it was possible to observe day scale variability, with flux variations up to a factor of about 3. The behavior of PMN J0948+0022 observed in this campaign and the calculated power carried out by its jet in the form of protons, electrons, radiation, and magnetic field are quite similar to that of blazars, specifically of flat-spectrum radio quasars. These results confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host relativistic jets with power similar to that of average blazars.

We present results from a numerical study of the multiphase interstellar medium in sub-Lyman-break galaxy protogalactic clumps. Such clumps are abundant at z = 3 and are thought to be a major contributor to damped Lyα absorption. We model the formation of winds from these clumps and show that during star formation (SF) episodes they feature outflows with neutral gas velocity widths up to several hundred  km s^-1. Such outflows might, in principle, produce the high velocity dispersion observed in damped Lyα absorbers (DLAs). Since the majority of DLAs have low SF rates, and only a small fraction of them might host a starburst at any given time, our median velocity width v₉₀ still falls short of the observed value. This discrepancy with observations could indicate that at l = 12 pc grid resolution the efficiency of conversion of feedback energy into hydrodynamical flows is less than optimal, even though these models show a remarkable improvement compared to the lower resolution runs. At l = 24 pc, the first signs of the multiphase medium are spotted; however, at this low resolution thermal injection of feedback energy cannot yet create hot expanding bubbles around star-forming regions—instead feedback tends to erase high-density peaks and suppress SF. At l = 12 pc, we see the formation of cold (≲300 K), dense (≳100 M_☉ pc⁻³) clouds that maintain SF while being compressed by the hot medium; at the same time a large fraction of feedback energy is channeled into low-density bubbles and winds. These winds often entrain compact neutral clumps which produce multi-component metal absorption lines.

Here we present an investigation into how cooling of the plasma influences the oscillation properties (e.g., eigenfunctions and eigenfrequencies) of transverse (i.e., kink) magnetohydrodynamic (MHD) waves in a compressible magnetic flux tube embedded in a gravitationally stratified and uniformly magnetized atmosphere. The cooling is introduced via a temperature-dependent density profile. A time-dependent governing equation is derived and an approximate zeroth-order solution is then obtained. From this the influence of cooling on the behavior of the eigenfrequencies and eigenfunctions of the transverse MHD waves is determined for representative cooling timescales. It is shown analytically, as the loop cools, how the amplitude of the perturbations is found to decrease as time increases. For cooling timescales of 900–2000 s (as observed in typical EUV loops), it is shown that the cooling has important and relevant influence on the damping times of loop oscillations. Next, the theory is put to the test. The damping due to cooling is fitted to a representative observation of standing kink oscillation of EUV loops. It is also shown with an explicit approximate analytical form, how the period of the fundamental and first harmonic of the kink mode changes with time as the loop cools. A consequence of this is that the value of the period ratio P₁/P₂, a tool that is popular in magneto-seismological studies in coronal diagnostics, decreases from the value of a uniform loop, 2, as the temperature decreases. The rate of change in P₁/P₂ is dependent upon the cooling timescale and is well within the observable range for typical EUV loops. Further to this, the magnitude of the anti-node shift of the eigenfunctions of the first harmonic is shown to continually increase as the loop cools, giving additional impetus to the use of spatial magneto-seismology of the solar atmosphere. Finally, we suggest that measurements of the rate of change in the eigenfunctions and eigenfrequencies of MHD oscillations can provide values for the cooling timescale and a further insight into the physics of coronal loops.

New statistical properties of dark matter halos in Lagrangian space are presented. Tracing back the dark matter particles constituting bound halos resolved in a series of N-body simulations, we measure quantitatively the correlations of the proto-halo's inertia tensors with the local tidal tensors and investigate how the correlation strength depends on the proto-halo's sphericity, local density, and filtering scale. It is shown that the majority of the proto-halos exhibit strong correlations between the two tensors provided that the tidal field is smoothed on the proto-halo's mass scale. The correlation strength is found to increase as the proto-halo's sphericity increases, as the proto-halo's mass increases, and as the local density becomes close to the critical value, δ_ec. It is also found that those peculiar proto-halos which exhibit exceptionally weak correlations between the two tensors tend to acquire higher specific angular momentum in Eulerian space, which is consistent with the linear tidal torque theory. In the light of our results, it is intriguing to speculate a hypothesis that the low surface brightness galaxies observed at present epoch correspond to the peculiar proto-halos with extreme low sphericity whose inertia tensors are weakly correlated with the local tidal tensors.

We present the discovery of substellar-mass companions to three stars by the ongoing Penn State–Toruń Planet Search conducted with the 9.2 m Hobby–Eberly Telescope. The K2-dwarf, BD+14 4559, has a 1.5 M_J minimum mass companion with the orbital period of 269 days and shows a non-linear, long-term radial velocity (RV) trend, which indicates a possible presence of another planet-mass body in the system. The K3-giant, HD 240210, exhibits RV variations that require modeling with multiple orbits, but the available data are not yet sufficient to do it unambiguously. A tentative, one-planet model calls for a 5.2 M_J minimum mass planet in a 502 day orbit around the star. The most massive of the three stars, the K2-giant, BD+20 2457, whose estimated mass is 2.8 ± 1.5 M_☉, has two companions with the respective minimum masses of 21.4 M_J and 12.5 M_J and orbital periods of 380 and 622 days. Depending on the unknown inclinations of the orbits, the currently very uncertain mass of the star, and the dynamical properties of the system, it may represent the first detection of two brown dwarf-mass companions orbiting a giant. The existence of such objects will have consequences for the interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars.

At energies ≳2 keV, active galactic nuclei (AGNs) are the source of the cosmic X-ray background (CXB). For AGN population synthesis models to replicate the peak region of the CXB (∼30 keV), a highly obscured and therefore nearly invisible class of AGN, known as Compton thick (CT) AGN, must be assumed to contribute nearly a third of the CXB. In order to constrain the CT fraction of AGNs and the CT number density we consider several hard X-ray AGN luminosity functions and the contribution of blazars to the CXB. Following the unified scheme, the radio AGN luminosity function is relativistically beamed to create a radio blazar luminosity function. An average blazar spectral energy density model is created to transform radio luminosity to X-ray luminosity. We find the blazar contribution to the CXB to be 12% in the 0.5–2 keV band, 7.4% in the 2–10 keV band, 8.9% in the 15–55 keV band, and 100% in the MeV region. When blazars are included in CXB synthesis models, CT AGNs are predicted to be roughly one-third of obscured AGNs, in contrast to the prediction of one half if blazars are not considered. Our model implies a BL Lac X-ray duty cycle of ∼13%, consistent with the concept of intermittent jet activity in low power radio galaxies.

Based on spectroscopic signatures, about one-third of known H₂O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These "disk maser candidates" are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v_sys < 20, 000 km s⁻¹). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130–500 km s⁻¹. Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2–7) ×10⁷M_☉) and mean disk radii (0.2–0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s⁻¹ <v_sys < 15, 000 km s⁻¹), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ∼0.1–1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGNs and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.

An interesting new high-energy pulsar sub-population is emerging following early discoveries of gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope (LAT). We present results from three-dimensional emission modeling, including the special relativistic effects of aberration and time-of-flight delays and also rotational sweepback of B-field lines, in the geometric context of polar cap (PC), outer gap (OG), and two-pole caustic (TPC) pulsar models. In contrast to the general belief that these very old, rapidly rotating neutron stars (NSs) should have largely pair-starved magnetospheres due to the absence of significant pair production, we find that most of the light curves are best fit by TPC and OG models, which indicates the presence of narrow accelerating gaps limited by robust pair production—even in these pulsars with very low spin-down luminosities. The gamma-ray pulse shapes and relative phase lags with respect to the radio pulses point to high-altitude emission being dominant for all geometries. We also find exclusive differentiation of the current gamma-ray MSP population into two MSP sub-classes: light curve shapes and lags across wavebands impose either pair-starved PC (PSPC) or TPC/OG-type geometries. In the first case, the radio pulse has a small lag with respect to the single gamma-ray pulse, while the (first) gamma-ray peak usually trails the radio by a large phase offset in the latter case. Finally, we find that the flux correction factor as a function of magnetic inclination and observer angles is typically of order unity for all models. Our calculation of light curves and flux correction factor for the case of MSPs is therefore complementary to the "ATLAS paper" of Watters et al. for younger pulsars.

We measure and analyze the energy, momentum, and mass feedback efficiencies due to radiation from active galactic nuclei (AGNs) in relatively large-scale outflows (from ∼0.01 to ∼10 pc). Our measurements are based on the two-dimensional (axisymmetric) and time-dependent radiation–hydrodynamical simulations recently presented in Kurosawa & Proga. In that paper, we studied outflows from a slowly rotating (sub-Keplerian) infalling gas driven by the energy and pressure of the radiation emitted by the AGNs. These simulations follow the dynamics of gas under the influence of the gravity of the central 10⁸ M_☉ black hole (BH) on scales from ∼0.01 to ∼10 pc. They self-consistently couple the accretion luminosity with the mass inflow rate at the smallest radius (our proxy for the mass-accretion rate, $\dot{M}_{\mathrm{a}}$). Over 30 simulations have been performed to investigate how the results depend on the gas density at the outer radius, ρ_o. A key feature of these simulations is that the radiation field and consequently the gas dynamics are axisymmetric, but not spherically symmetric. Therefore, the gas inflow and outflow can occur at the same time. We compare our $\dot{M}_{\mathrm{a}}$–ρ_o relation with that predicted by the Bondi accretion model. For high luminosities comparable to the Eddington limit, the power-law fit $(\dot{M}_{\mathrm{a}} \propto \rho _{\mathrm{o}}^{q})$ to our models yields q ≈ 0.5 instead of q = 1.0, which is predicted by the Bondi model. This difference is caused by the outflows which are important for the overall mass budget at high luminosities. The maximum momentum and mass feedback efficiencies found in our models are ∼10⁻² and ∼10⁻¹, respectively. However, the outflows are much less important energetically: the thermal and kinetic powers in units of the radiative luminosity are ∼10⁻⁵ and ∼10⁻⁴, respectively. In addition, the efficiencies do not increase monotonically with the accretion luminosity but rather peak around the Eddington limit beyond which a steady-state disk–wind-like solution exists. Our energy feedback efficiencies are significantly lower than 0.05, which is required in some cosmological and galaxy merger simulations. The low feedback efficiencies found here could have significant implications on the mass growth of super massive BHs in the early universe. We stress, however, that we have not considered the innermost parts of the accretion and outflow where radiation and matter interact most strongly. The feedback from this region could have efficiencies significantly above the low values found here.

Resistivity and viscosity have a significant role in establishing the energy levels in turbulence driven by the magnetorotational instability (MRI) in local astrophysical disk models. This study uses the Athena code to characterize the effects of a constant shear viscosity ν and Ohmic resistivity η in unstratified shearing box simulations with a net toroidal magnetic flux. A previous study of shearing boxes with zero net magnetic field performed with the ZEUS code found that turbulence dies out for values of the magnetic Prandtl number, P_m = ν/η, below P_m ∼ 1; for P_m ≳ 1, time- and volume-averaged stress levels increase with P_m. We repeat these experiments with Athena and obtain consistent results. Next, the influence of viscosity and resistivity on the toroidal field MRI is investigated both for linear growth and for fully developed turbulence. In the linear regime, a sufficiently large ν or η can prevent MRI growth; P_m itself has little direct influence on growth from linear perturbations. By applying a range of values for ν and η to an initial state consisting of fully developed turbulence in the presence of a background toroidal field, we investigate their effects in the fully nonlinear system. Here, increased viscosity enhances the turbulence, and the turbulence decays only if the resistivity is above a critical value; turbulence can be sustained even when P_m < 1, in contrast to the zero net field model. While we find preliminary evidence that the stress converges to a small range of values when ν and η become small enough, the influence of dissipation terms on MRI-driven turbulence for relatively large η and ν is significant, independent of field geometry.

Magnetars are young neutron stars with extreme magnetic fields (B ≳ 10¹⁴–10¹⁵ G). How these fields relate to the properties of their progenitor stars is not yet clearly established. However, from the few objects associated with young clusters it has been possible to estimate the initial masses of the progenitors, with results indicating that a very massive progenitor star (M_prog> 40 M$_{\normalsize \odot }$) is required to produce a magnetar. Here, we present adaptive-optics assisted Keck/NIRC2 imaging and Keck/NIRSPEC spectroscopy of the cluster associated with the magnetar SGR 1900+14, and report that the initial progenitor star mass of the magnetar was a factor of 2 lower than this limit, M_prog = 17 ± 2 M$_{\normalsize \odot }$. Our result presents a strong challenge to the concept that magnetars can only result from very massive progenitors. Instead, we favor a mechanism which is dependent on more than just initial stellar mass for the production of these extreme magnetic fields, such as the "fossil-field" model or a process involving close binary evolution.

We report the results of the analysis of high-resolution photospheric line spectra obtained with the UVES instrument on the VLT for a sample of 15 solar-type stars selected from a recent survey of the distribution of H and K chromospheric line strengths in the solar-age open cluster M67. We find upper limits to the projected rotation velocities that are consistent with solar-like rotation (i.e., v sin i≲ 2–3 km s⁻¹) for objects with Ca ii chromospheric activity within the range of the contemporary solar cycle. Two solar-type stars in our sample exhibit chromospheric emission well in excess of even solar maximum values. In one case, Sanders 1452, we measure a minimum rotational velocity of v sin i = 4 ± 0.5 km s⁻¹, or over twice the solar equatorial rotational velocity. The other star with enhanced activity, Sanders 747, is a spectroscopic binary. We conclude that high activity in solar-type stars in M67 that exceeds solar levels is likely due to more rapid rotation rather than an excursion in solar-like activity cycles to unusually high levels. We estimate an upper limit of 0.2% for the range of brightness changes occurring as a result of chromospheric activity in solar-type stars and, by inference, in the Sun itself. We discuss possible implications for our understanding of angular momentum evolution in solar-type stars, and we tentatively attribute the rapid rotation in Sanders 1452 to a reduced braking efficiency.

The formation of thick stellar disks in spiral galaxies is studied. Simulations of gas-rich young galaxies show formation of internal clumps by gravitational instabilities, clump coalescence into a bulge, and disk thickening by strong stellar scattering. The bulge and thick disks of modern galaxies may form this way. Simulations of minor mergers make thick disks too, but there is an important difference. Thick disks made by internal processes have a constant scale height with galactocentric radius, but thick disks made by mergers flare. The difference arises because in the first case, perpendicular forcing and disk-gravity resistance are both proportional to the disk column density, so the resulting scale height is independent of this density. In the case of mergers, perpendicular forcing is independent of the column density and the low-density regions get thicker; the resulting flaring is inconsistent with observations. Late-stage gas accretion and thin-disk growth are shown to preserve the constant scale heights of thick disks formed by internal evolution. These results reinforce the idea that disk galaxies accrete most of their mass smoothly and acquire their structure by internal processes, in particular through turbulent and clumpy phases at high redshift.

Models of accretion disks around a star in a binary system predict that the disk will have a retrograde precession with a period a factor of ∼10 times the orbital period. If the star+disk system ejects a bipolar outflow, this outflow will be subject to the effects of both the orbital motion and the precession. We present an analytic, ballistic model and a three-dimensional gasdynamical simulation of a bipolar outflow from a source in a circular orbit, and with a precessing outflow axis. We find that this combination results in a jet/counterjet system with a small spatial scale, reflection-symmetric spiral (resulting from the orbital motion) and a larger-scale, point-symmetric spiral (resulting from the longer period precession). These results provide interesting possibilities for modeling specific Herbig–Haro jets and bipolar planetary nebulae.

We report the discovery of a multiply lensed Lyα emitter at z = 3.90 behind the massive cluster WARPS J1415.1+3612 at z = 1.026. Images taken by the Hubble Space Telescope using the Advanced Camera for Surveys reveal a complex lensing system that produces a prominent, highly magnified arc and a triplet of smaller arcs grouped tightly around a spectroscopically confirmed cluster member. Spectroscopic observations using the Faint Object Camera and Spectrograph on Subaru confirm strong Lyα emission in the source galaxy and provide the redshifts for more than 21 cluster members with a velocity dispersion of 807 ± 185 km s⁻¹. Assuming a singular isothermal sphere profile, the mass within the Einstein ring (7.13 ±  038) corresponds to a central velocity dispersion of 686⁺¹⁵₋₁₉ km s⁻¹ for the cluster, consistent with the value estimated from cluster member redshifts. Our mass profile estimate from combining strong lensing and dynamical analyses is in good agreement with both X-ray and weak lensing results.

We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo Cluster and in the field, which show that 52% of the dEs (1) are rotationally supported, (2) exhibit structural signs of typical rotating systems such as disks, bars, or spiral arms, (3) are younger (∼3 Gyr) than non-rotating dEs, and (4) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late-type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting disks are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment, and ram pressure stripping).

We demonstrate that stars beyond the virial radii of galaxies may be generated by the gravitational impulse received by a satellite as it passes through the pericenter of its orbit around its parent. These stars may become energetically unbound (escaped stars), or may travel to further than a few virial radii for longer than a few Gyr, but still remain energetically bound to the system (wandering stars). Larger satellites (10%–100% the mass of the parent), and satellites on more radial orbits are responsible for the majority of this ejected population. Wandering stars could be observable on Mpc scales via classical novae, and on 100 Mpc scales via Type Ia supernova. The existence of such stars would imply a corresponding population of barely bound, old, high-velocity stars orbiting the Milky Way, generated by the same physical mechanism during the Galaxy's formation epoch. Sizes and properties of these combined populations should place some constraints on the orbits and masses of the progenitor objects from which they came, providing insight into the merging histories of galaxies in general and the Milky Way in particular.

We present new far-ultraviolet (far-UV) spectra of an oxygen-rich knot in the Large Magellanic Cloud supernova remnant N132D, obtained with the Hubble Space Telescope (HST)-Cosmic Origins Spectrograph (COS). Moderate-resolution (Δv ≈ 200 km s⁻¹) spectra in the HST far-UV bandpass (1150 Å ≲ λ ≲ 1750 Å) show emission from several ionization states of oxygen as well as trace amounts of other species. We use the improvements in sensitivity and resolving power offered by COS to separate contributions from different velocity components within the remnant, as well as emission from different species within the oxygen-rich knot itself. This is the first time that compositional and velocity structure in the ultraviolet emission lines from N132D have been resolved. No nitrogen is detected in N132D, and multiple carbon species are found at velocities inconsistent with the main oxygen component. We find helium and silicon to be associated with the oxygen-rich knot and use the reddening-corrected line strengths of O iii], O iv], O v, and Si iv to constrain the composition and physical characteristics of this oxygen-rich knot. We find that models with a silicon-to-oxygen abundance ratio of N(Si)/N(O) = 10⁻² can reproduce the observed emission for a shock velocity of ∼130 km s⁻¹, implying a mass of ∼50 M_☉ for the N132D progenitor star.

NGC 6302 is one of the highest ionization planetary nebulae (PNe) known and shows emission from species with ionization potential > 300 eV. The temperature of the central star must be > 200,000 K to photoionize the nebula, and has been suggested to be up to ∼400,000 K. On account of the dense dust and molecular disk, the central star has not convincingly been directly imaged until now. NGC 6302 was imaged in six narrowband filters by Wide Field Camera 3 on the Hubble Space Telescope as part of the Servicing Mission 4 Early Release Observations. The central star is directly detected for the first time, and is situated at the nebula center on the foreground side of the tilted equatorial disk. The magnitudes of the central star have been reliably measured in two filters (F469N and F673N). Assuming a hot blackbody, the reddening has been measured from the (4688–6766 Å) color and a value of c = 3.1, A_v = 6.6 mag determined. A G-K main-sequence binary companion can be excluded. The position of the star on the H–R diagram suggests a fairly massive PN central star of about 0.64 M_☉ close to the white dwarf cooling track. A fit to the evolutionary tracks for (T, L, t) = (200,000 K, 2000 L_☉, 2200 yr), where t is the nebular age, is obtained; however, the luminosity and temperature remain uncertain. The model tracks predict that the star is rapidly evolving, and fading at a rate of almost 1% per year. Future observations could test this prediction.

We report a chromospheric jet lasting for more than 1 hr observed by the Hinode Solar Optical Telescope in unprecedented detail. The ejection occurred in three episodes separated by 12–14 minutes, with the amount and velocity of material decreasing with time. The upward velocities range from 438 to $33\,\mathop {\rm km}\nolimits \,\mathop {\rm s}\nolimits ^{-1}$, while the downward velocities of the material falling back have smaller values (mean: $-56 \mathop {\rm km}\nolimits \,\mathop {\rm s}\nolimits ^{-1}$) and a narrower distribution (standard deviation: $14 \mathop {\rm km}\nolimits \,\mathop {\rm s}\nolimits ^{-1}$). The average acceleration inferred from parabolic spacetime tracks is $141\, \mathop {\rm m}\nolimits \, {\rm s^{-2}}$, a fraction of the solar gravitational acceleration. The jet consists of fine threads (05–2'' wide), which exhibit coherent, oscillatory transverse motions perpendicular to the jet axis and about a common equilibrium position. These motions propagate upward along the jet, with the maximum phase speed of $744 \pm 11\,\mathop {\rm km}\nolimits \,\mathop {\rm s}\nolimits ^{-1}$at the leading front of the jet. The transverse oscillation velocities range from 151 to $26 \,\mathop {\rm km}\nolimits \,\mathop {\rm s}\nolimits ^{-1}$, amplitudes from 6.0 to $1.9 \,\mathop {\rm Mm}\nolimits$, and periods from 250 to $536\,\mathop {\rm s}\nolimits$. The oscillations slow down with time and cease when the material starts to fall back. The falling material travels along almost straight lines in the original direction of ascent, showing no transverse motions. These observations are consistent with the scenario that the jet involves untwisting helical threads, which rotate about the axis of a single large cylinder and shed magnetic helicity into the upper atmosphere.

We revisit recent claims of a significant detection of a bulk flow of distant galaxy clusters. We do not find a statistically significant detection of a bulk flow. Instead we find that cosmic microwave background correlations between the eight Wilkinson Microwave Anisotropy Probe channels used in this analysis decrease the inferred significance of the detection to 0.7σ.

Solar flare hard X-ray (HXR) spectra from Reuven Ramaty High Energy Solar Spectrometer (RHESSI) are normally interpreted in terms of purely collisional electron beam propagation, ignoring spatial evolution and collective effects. In this Letter, we present self-consistent numerical simulations of the spatial and temporal evolution of an electron beam subject to collisional transport and beam-driven Langmuir wave turbulence. These wave–particle interactions represent the background plasma's response to the electron beam propagating from the corona to chromosphere and occur on a far faster timescale than Coulomb collisions. From these simulations, we derive the mean electron flux spectrum, comparable to such spectra recovered from high-resolution HXRs observations of solar flares with RHESSI. We find that a negative spectral index (i.e., a spectrum that increases with energy), or local minima when including the expected thermal spectral component at low energies, occurs in the standard thick-target model, when Coulomb collisions are only considered. The inclusion of wave–particle interactions does not produce a local minimum, maintaining a positive spectral index. These simulations are a step toward a more complete treatment of electron transport in solar flares and suggest that a flat spectrum (spectral index of 0–1) down to thermal energies maybe a better approximation instead of a sharp cutoff in the injected electron spectrum.

We report on the detection of the two shortest period non-interacting white dwarf binary systems. These systems, SDSS J143633.29+501026.8 and SDSS J105353.89+520031.0, were identified by searching for radial velocity variations in the individual exposures that make up the published spectra from the Sloan Digital Sky Survey. We followed up these systems with time series spectroscopy to measure the period and mass ratios of these systems. Although we only place a lower bound on the companion masses, we argue that they must also be white dwarf stars. With periods of approximately 1 hr, we estimate that the systems will merge in less than 100 Myr, but the merger product will likely not be massive enough to result in a Type 1a supernova.

A list of 205 γ-ray strong objects was reported recently as a result of a three-month integration with the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. We attempted identification of these objects, cross-correlating the γ-ray positions with very long baseline interferometry (VLBI) positions of a large all-sky sample of extragalactic radio sources selected on the basis of their parsec-scale flux density. The original associations reported by the Fermi team are confirmed, and six new identifications are suggested. A Monte Carlo analysis shows that the fraction of chance associations in our analysis is less than 5%, and confirms that the vast majority of γ-ray bright extragalactic sources are radio-loud blazars with strong parsec-scale jets. A correlation between the parsec-scale radio and γ-ray flux is supported by our analysis of a complete VLBI flux-density-limited sample of extragalactic jets. The effectiveness of using a VLBI catalog to find associations between γ-ray detections and compact extragalactic radio sources, especially near the Galactic plane, is demonstrated. It is suggested that VLBI catalogs should be used for future identification of Fermi/LAT objects.

We present a 100 ks Suzaku observation of the dMe flare star EV Lac, in which the star was captured undergoing a moderate 1500 s flare. During the flare, the count rate increased by about a factor of 50 and the spectrum showed overall enhanced element abundances relative to quiescence. While the quiescent element abundances confirm the inverse first ionization potential (FIP) effect previously documented for EV Lac, with relatively higher depletions for low FIP elements, abundances during the flare spectra show a composition closer to that of the stellar photosphere. We discuss these results in the context of models that explain abundance fractionation in the stellar chromosphere as a result of the ponderomotive force due to Alfvén waves. Stars with FIP or inverse FIP effects arising from differently directed ponderomotive forces may have quite different abundance signatures in their evaporated chromospheric plasma during flares, if the same ponderomotive force also affects thermal conduction downward from the corona. The regulation of the thermal conductivity by the ponderomotive force requires a level of turbulence that is somewhat higher than is normally assumed, but plausible in filamentary conduction models.

We determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity (VOD), which covers almost $1000\ \deg ^2$ on the sky, based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances. Despite the low precision of the method for individual stars, we derive [Fe/H] = −2.0  ±   0.1(internal) ± 0.5(systematic) for the metal abundance of the VOD from photometric measurements of 0.7 million stars in the northern Galactic hemisphere with heliocentric distances from ∼10 kpc to ∼20 kpc. The metallicity of the VOD is indistinguishable, within Δ[Fe/H] ⩽ 0.2, from that of field halo stars covering the same distance range. This initial application suggests that the Sloan Digital Sky Survey gri passbands can be used to probe the properties of main-sequence stars beyond ∼10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband.

Using deep Chandra observations of the Hydra A galaxy cluster, we examine the metallicity structure near the central galaxy and along its powerful radio source. We show that the metallicity of the intracluster medium is enhanced by up to 0.2 dex along the radio jets and lobes compared to the metallicity of the undisturbed gas. The enhancements extend from a radius of 20 kpc from the central galaxy to a distance of ∼120 kpc. We estimate the total iron mass that has been transported out of the central galaxy to be between 2 × 10⁷ M_☉ and 7 × 10⁷ M_☉, which represents 10%–30% of the iron mass within the central galaxy. The energy required to lift this gas is roughly 1% to 5% of the total energetic output of the active galactic nuclei. Evidently, Hydra A's powerful radio source is able to redistribute metal-enriched, low entropy gas throughout the core of the galaxy cluster. The short re-enrichment timescale <10⁹ yr implies that the metals lost from the central galaxy will be quickly replenished.

Analytical relations are derived for the amplitude of astrometric, photometric, and radial velocity (RV) perturbations caused by a single rotating spot. The relative power of the starspot jitter is estimated and compared with the available data for κ¹ Ceti and HD 166435, as well as with numerical simulations for κ¹ Ceti and the Sun. A Sun-like star inclined at i = 90° at 10 pc is predicted to have an rms jitter of 0.087 μas in its astrometric position along the equator, and 0.38 m s⁻¹ in radial velocities. If the presence of spots due to stellar activity is the ultimate limiting factor for planet detection, the sensitivity of SIM Lite to Earth-like planets in habitable zones is about an order of magnitude higher than the sensitivity of prospective ultra-precise RV observations of nearby stars.

Current X-ray observatories make it possible to follow the evolution of transient and variable X-ray binaries across a broad range in luminosity and source behavior. In such studies, it can be unclear whether evolution in the low-energy portion of the spectrum should be attributed to evolution in the source, or instead to evolution in neutral photoelectric absorption. Dispersive spectrometers make it possible to address this problem. We have analyzed a small but diverse set of X-ray binaries observed with the Chandra High Energy Transmission Grating Spectrometer across a range in luminosity and different spectral states. The column density in individual photoelectric absorption edges remains constant with luminosity, both within and across source spectral states. This finding suggests that absorption in the interstellar medium strongly dominates the neutral column density observed in spectra of X-ray binaries. Consequently, evolution in the low-energy spectrum of X-ray binaries should properly be attributed to evolution in the source spectrum. We discuss our results in the context of X-ray binary spectroscopy with current and future X-ray missions.

We investigate consequences of the discovery that Fe ii emission in quasars, one of the spectroscopic signatures of "Eigenvector 1," may originate in infalling clouds. Eigenvector 1 correlates with the Eddington ratio L/L_Edd so that Fe ii/Hβ increases as L/L_Edd increases. We show that the "force multiplier," the ratio of gas opacity to electron scattering opacity, is ∼10³–10⁴ in Fe ii-emitting gas. Such gas would be accelerated away from the central object if the radiation force is able to act on the entire cloud. As had previously been deduced, infall requires that the clouds have large column densities so that a substantial amount of shielded gas is present. The critical column density required for infall to occur depends on L/L_Edd, establishing a link between Eigenvector 1 and the Fe ii/Hβ ratio. We see predominantly the shielded face of the infalling clouds rather than the symmetric distribution of emitters that has been assumed. The Fe ii spectrum emitted by the shielded face is in good agreement with observations thus solving several long-standing mysteries in quasar emission lines.

Most black hole binaries show large changes in X-ray luminosity caused primarily by variations in mass accretion rate. An important question for understanding black hole accretion and jet production is whether the inner edge of the accretion disk recedes at low accretion rate. Measurements of the location of the inner edge (R_in) can be made using iron emission lines that arise due to fluorescence of iron in the disk, and these indicate that R_in is very close to the black hole at high and moderate luminosities (≳1% of the Eddington luminosity, L_Edd). Here, we report on X-ray observations of the black hole GX 339 − 4 in the hard state by Suzaku and the Rossi X-ray Timing Explorer that extend iron line studies to 0.14% L_Edd and show that R_in increases by a factor of >27 over the value found when GX 339 − 4 was bright. The exact value of R_in depends on the inclination of the inner disk (i), and we derive 90% confidence limits of R_in > 35R_g at i = 0° and R_in > 175R_g at i = 30°. This provides direct evidence that the inner portion of the disk is not present at low luminosity, allowing for the possibility that the inner disk is replaced by advection- or magnetically dominated accretion flows.

We extract synthetic photon spectra from first-principles particle-in-cell simulations of relativistic shocks propagating in unmagnetized pair plasmas. The two basic ingredients for the radiation, namely accelerated particles and magnetic fields, are produced self-consistently as part of the shock evolution. We use the method of Hededal & Nordlund and compute the photon spectrum via Fourier transform of the electric far field from a large number of particles, sampled directly from the simulation. We find that the spectrum from relativistic collisionless shocks is entirely consistent with synchrotron radiation in the magnetic fields generated by Weibel instability. We can recover the so-called "jitter" regime only if we artificially reduce the strength of the electromagnetic fields, such that the wiggler parameter K ≡ qBλ/mc² becomes much smaller than unity (B and λ are the strength and scale of the magnetic turbulence, respectively). These findings may place constraints on the origin of non-thermal emission in astrophysics, especially for the interpretation of the hard (harder than synchrotron) low-frequency spectrum of gamma-ray bursts.

Crystalline silicates are observed in many protoplanetary disks and some dust shells around evolved stars. The peak positions of infrared (IR) spectra of forsterite, which is the most abundant circumstellar silicate, vary with dust temperature, composition, size, and crystallinity. However, there is another important factor that affects IR spectra, which is the shape with a specific crystallographic orientation called the "crystallographically anisotropic shape." We focused on anisotropic evaporation of crystalline forsterite as one of the possible processes that change the crystallographically anisotropic shape of forsterite grains, and carried out evaporation experiments of single crystals of forsterite in hydrogen gas (0.01–10 Pa) and at temperatures of 1150–1660°C. Forsterite evaporated anisotropically in all experimental conditions, and the anisotropy depended on temperature and hydrogen gas pressure. The results enabled us to calculate crystallographically anisotropic shapes of heated forsterite as a function of temperature and hydrogen pressure, and their corresponding IR spectra. Distinctly, different sets of peak positions were seen in IR spectra of grains with different combination of shapes and their orientation reflecting the heating conditions. The results were applied to the IR spectrum of a protoplanetary disk, HD100546, which suggests that forsterite dust particles that experienced evaporation exist with dominant secondarily fragmented forsterite formed by small-body collisions. We propose that detailed IR spectroscopy of forsterite, and probably other anisotropic crystals, is a new tool to estimate temperature and pressure conditions of circumstellar environments where dust formed.

We identify 13 sets of multiply-lensed galaxies around MACS J0717.5+3745 (z = 0.546), outlining a very large tangential critical curve of major axis ∼28, filling the field of the Hubble Space Telescope/Advanced Camera for Surveys. The equivalent circular Einstein radius is θ_e = 55'' ± 3'' (at an estimated source redshift of z_s ∼ 2.5), corresponding to r_e ≃ 350 ± 20 kpc at the cluster redshift, nearly three times greater than that of A1689 (r_e ≃ 140 kpc for z_s = 2.5). The mass enclosed by this critical curve is very large, 7.4 ± 0.5 × 10¹⁴M_☉ and only weakly model dependent, with a relatively shallow mass profile within r < 250 kpc, reflecting the unrelaxed appearance of this cluster. This shallow profile generates a much higher level of magnification than the well-known relaxed lensing clusters of higher concentration, so that the area of sky exceeding a magnification of >10 times, is ≃3.5□' for sources with z ≃ 8, making MACS J0717.5+3745 a compelling target for accessing faint objects at high redshift. We calculate that only one such cluster, with θ_e ⩾ 55'', is predicted within ∼10⁷ Universes with z ⩾ 0.55, corresponding to a virial mass ⩾3 × 10¹⁵M_☉, for the standard ΛCDM (WMAP5 parameters with 2σ uncertainties).