Table of contents

We present the results of a high-resolution spectral differential imaging survey of 12 nearby, relatively young field L dwarfs (⩽1 Gyr) carried out with the Hubble Space Telescope/NICMOS to search for planetary mass companions at small physical separations from their host. The survey resolved two brown dwarf binaries: the L dwarf system Kelu-1 AB and the newly discovered L/T transition system 2MASS 031059+164815 AB. For both systems, common proper motion has already been confirmed in follow-up observations which have been published elsewhere. The derived separations of the binaries are smaller than 6 AU and consistent with previous brown dwarf binary statistics. Their mass ratios of q ⩾ 0.8 confirm the preference for equal-mass systems similar to a large number of other surveys. Furthermore, we found tentative evidence for a companion to the L4 dwarf 2MASSW 033703−175807, straddling the brown dwarf/planetary mass boundary and revealing an uncommonly low-mass ratio system (q ≈ 0.2) compared to the vast majority of previously found brown dwarf binaries. With a derived minimum mass of 10–15 M_Jup a planetary nature of the secondary cannot be ruled out yet. However, it seems more likely to be a very low mass brown dwarf secondary at the border of the spectral T/Y transition regime, primarily due to its similarities to recently found very cool T dwarfs. This would make it one of the closest resolved brown dwarf binaries (0087 ± 0015, corresponding to 2.52 ± 0.44 AU at a distance of 29 pc) with the coolest (T_eff ≈ 600–630 K) and least massive companion to any L or T dwarf.

Recent measurements of hot and cold spots on the cosmic microwave background (CMB) sky suggest the presence of super-structures on (>100 h⁻¹ Mpc) scales. We develop a new formalism to estimate the expected amplitude of temperature fluctuations due to the integrated Sachs–Wolfe (ISW) effect from prominent quasi-linear structures. Applying the developed tools to the observed ISW signals from voids and clusters in catalogs of galaxies at redshifts z < 1, we find that they indeed imply a presence of quasi-linear super-structures with a comoving radius of 100 ∼ 300 h⁻¹ Mpc and a density contrast |δ| ∼ O(0.1). We also find that the observed ISW signals are at odds with the concordant Λ cold dark matter model that predicts Gaussian primordial perturbations at ≳3σ level. We confirm that the mean temperature around the CMB cold spot in the southern Galactic hemisphere filtered by a compensating top-hat filter deviates from the mean value at ∼3σ level, implying that a quasi-linear supervoid or an underdensity region surrounded by a massive wall may reside at low redshifts z < 0.3 and the actual angular size (16°–17°) may be larger than the apparent size (4°–10°) discussed in literature. Possible solutions are briefly discussed.

We present the broadband X-ray power spectral density (PSD) function of the X-ray-luminous Seyfert 1.2 NGC 7469, measured from Rossi X-ray Timing Explorer monitoring data and two XMM-Newton observations. We find significant evidence for a turnover in the 2–10 keV PSD at a temporal frequency of 2.0^+3.0_−0.8 × 10⁻⁶ Hz or 1.0^+3.0_−0.6 × 10⁻⁶ Hz, depending on the exact form of the break (sharply broken or slowly bending power law, respectively). The "surrogate" Monte Carlo method of Press et al. was used to map out the probability distributions of PSD model parameters and obtain reliable uncertainties (68% confidence limits quoted here). The corresponding break timescale of 5.8 ± 3.5 days or 11.6^+17.5_−8.7 days, respectively, is consistent with the empirical relation between PSD break timescale, black hole mass, and bolometric luminosity of McHardy et al. Compared to the 2–10 keV PSD, the 10–20 keV PSD has a much flatter shape at high temporal frequencies, and no PSD break is significantly detected, suggesting an energy-dependent evolution not unlike that exhibited by several Galactic black hole systems.

We calculate the location and stability of the L₄ and L₅ Lagrange equilibrium points in the circular restricted three-body problem as the binary system evolves via gravitational radiation losses. Relative to the purely Newtonian case, we find that the L₄ equilibrium point moves toward the secondary mass and becomes slightly less stable, while the L₅ point moves away from the secondary and gains in stability. We discuss a number of astrophysical applications of these results, in particular as a mechanism for producing electromagnetic counterparts to gravitational-wave signals.

The starburst phenomenon can shape the evolution of the host galaxy and the surrounding intergalactic medium. The extent of the evolutionary impact is partly determined by the duration of the starburst, which has a direct correlation with both the amount of stellar feedback and the development of galactic winds, particularly for smaller mass dwarf systems. We measure the duration of starbursts in twenty nearby, ongoing, and "fossil" starbursts in dwarf galaxies based on the recent star formation histories derived from resolved stellar population data obtained with the Hubble Space Telescope. Contrary to the shorter times of 3–10 Myr often cited, the starburst durations we measure range from 450to650 Myr in fifteen of the dwarf galaxies and up to 1.3 Gyr in four galaxies; these longer durations are comparable to or longer than the dynamical timescales for each system. The same feedback from massive stars that may quench the flickering star formation does not disrupt the overall burst event in our sample of galaxies. While five galaxies present fossil bursts, fifteen galaxies show ongoing bursts and thus the final durations may be longer than we report here for these systems. One galaxy shows a burst that has been ongoing for only 20 Myr; we are likely seeing the beginning of a burst event in this system. Using the duration of the starbursts, we calculate that the bursts deposited 10^53.9–10^57.2 erg of energy into the interstellar medium through stellar winds and supernovae, and produced 3%−26% of the host galaxy's mass.

RX J1713.7−3946 is one of the TeV γ-ray supernova remnants (SNRs) emitting synchrotron X-rays. The SNR is associated with molecular gas located at ∼1 kpc. We made new molecular observations toward the dense cloud cores, peaks A, C, and D, in the SNR in the ¹²CO(J = 2–1) and ¹³CO(J = 2–1) transitions at an angular resolution of 90''. The most intense core in ¹³CO, peak C, was also mapped in the ¹²CO(J = 4–3) transition at an angular resolution of 38''. Peak C shows strong signs of active star formation including bipolar outflow and a far-infrared protostellar source, and has a steep gradient with a r^−2.2±0.4 variation in the average density within radius r. Peak C and the other dense cloud cores are rim-brightened in synchrotron X-rays, suggesting that the dense cloud cores are embedded within or on the outer boundary of the SNR shell. This confirms the earlier suggestion that the X-rays are physically associated with the molecular gas. We present a scenario where the densest molecular core, peak C, survived the blast wave and is now embedded within the SNR. Numerical simulations of the shock–cloud interaction indicate that a dense clump can indeed survive shock erosion, since the shock propagation speed is stalled in the dense clump. Additionally, the shock–cloud interaction induces turbulence and magnetic field amplification around the dense clump that may facilitate particle acceleration in the lower-density inter-clump space leading to enhanced synchrotron X-rays around dense cores.

We present an analysis of Spitzer-IRS spectroscopic maps of the L1157 protostellar outflow in the H₂ pure-rotational lines from S(0) to S(7). The aim of this work is to derive the physical conditions pertaining to the warm molecular gas and study their variations within the flow. The mid-IR H₂ emission follows the morphology of the precessing flow, with peaks correlated with individual CO clumps and H₂ 2.12 μm ro-vibrational emission. More diffuse emission delineating the CO cavities is detected only in the low-laying transitions, with J_lower⩽ 2. The H₂ line images have been used to construct two-dimensional maps of N(H₂), H₂ ortho-to-para ratio (OPR), and temperature spectral index β, in the assumption of a gas temperature stratification where the H₂ column density varies as T^−β. Variations of these parameters are observed along the flow. In particular, the OPR ranges from ∼0.6 to 2.8, highlighting the presence of regions subject to recent shocks where the OPR has not had time yet to reach the equilibrium value. Near-IR spectroscopic data on ro-vibrational H₂ emission have been combined with the mid-IR data and used to derive additional shock parameters in the brightest blueshifted and redshifted emission knots. A high abundance of atomic hydrogen (H/H₂ ∼ 0.1–0.3) is implied by the observed H₂ column densities, assuming n(H₂) values as derived by independent SiO observations. The presence of a high fraction of atomic hydrogen indicates that a partially dissociative shock component should be considered for the H₂ excitation in these localized regions. However, planar shock models, either of C- or J-type, are not able to consistently reproduce all the physical parameters derived from our analysis of the H₂ emission. Globally, H₂ emission contributes to about 50% of the total shock radiated energy in the L1157 outflow. We find that the momentum flux through the shocks derived from the radiated luminosity is comparable to the thrust of the associated molecular outflow, supporting the scenario where the latter is driven by the shock working surface.

The evolution of compact groups of galaxies may represent one of the few places in the nearby universe in which massive galaxies are being forged through a complex set of processes involving tidal interaction, ram-pressure stripping, and perhaps finally "dry mergers" of galaxies stripped of their cool gas. Using collisionless N-body simulations, we propose a possible scenario for the formation of one of the best-studied compact groups: Stephan's Quintet. We define a serial approach which allows us to consider the history of the group as a sequence of galaxy–galaxy interactions seen as relatively separate events in time, but chained together in such a way as to provide a plausible scenario that ends in the current configuration of the galaxies. By covering a large set of parameters, we claim that it is very unlikely that both major tidal tails of the group have been created by the interaction between the main galaxy and a single intruder. We propose instead a scenario based on two satellites orbiting the main disk, plus the recent involvement of an additional interloper, coming from the background at high speed. This purely N-body study of the quintet will provide a parameter-space exploration of the basic dynamics of the group that can be used as a basis for a more sophisticated N-body/hydrodynamic study of the group that is necessary to explain the giant shock structure and other purely gaseous phenomena observed in both the cold, warm and hot gas in the group.

The solar photosphere is depleted in refractory elements compared to most solar twins, with the degree of depletion increasing with an element's condensation temperature. Here, I show that adding 4 Earth masses of Earth-like and carbonaceous-chondrite-like material to the solar convection zone brings the Sun's composition into line with the mean value for the solar twins. The observed solar composition could have arisen if the Sun's convection zone accreted material from the solar nebula that was depleted in refractory elements due to the formation of the terrestrial planets and ejection of rocky protoplanets from the asteroid belt. Most solar analogs are missing 0–10 Earth masses of rocky material compared to the most refractory-rich stars, providing an upper limit to the mass of rocky terrestrial planets that they possess. The missing mass is correlated with stellar metallicity. This suggests that the efficiency of planetesimal formation increases with stellar metallicity. Stars with and without known giant planets show a similar distribution of abundance trends. If refractory depletion is a signature of the presence of terrestrial planets, this suggests that there is not a strong correlation between the presence of terrestrial and giant planets in the same system.

Motivated by the solar composition problem and by using the recently developed linear solar model approach, we analyze the role of opacity and metals in the Sun. After a brief discussion of the relation between the effects produced by a variation of composition and those produced by a modification of the radiative opacity, we calculate numerically the opacity kernels that, in a linear approximation, relate an arbitrary opacity variation to the corresponding modification of the solar observable properties. We use these opacity kernels to discuss the present constraints on opacity (and composition) provided by helioseismic and solar neutrino data.

We present a comprehensive study of white dwarf collisions as an avenue for creating type Ia supernovae. Using a smooth particle hydrodynamics code with a 13-isotope, α-chain nuclear network, we examine the resulting ⁵⁶Ni yield as a function of total mass, mass ratio, and impact parameter. We show that several combinations of white dwarf masses and impact parameters are able to produce sufficient quantities of ⁵⁶Ni to be observable at cosmological distances. We find that the ⁵⁶Ni production in double-degenerate white dwarf collisions ranges from sub-luminous to the super-luminous, depending on the parameters of the collision. For all mass pairs, collisions with small impact parameters have the highest likelihood of detonating, but ⁵⁶Ni production is insensitive to this parameter in high-mass combinations, which significantly increases their likelihood of detection. We also find that the ⁵⁶Ni dependence on total mass and mass ratio is not linear, with larger-mass primaries producing disproportionately more ⁵⁶Ni than their lower-mass secondary counterparts, and symmetric pairs of masses producing more ⁵⁶Ni than asymmetric pairs.

Quantum reactive calculations, under the general conditions of early universe chemistry, are carried out for the reaction of H⁺ ions, expected to be abundant projectiles at those redshift values, with LiH molecules (ν = 0). The results indicate that the outgoing flux, due to the special kinematics induced by the exothermic potential energy surface, is mostly distributed into the LiH survival channels of the fast exothermic reaction. The final, ab initio destruction rates, which are forming H⁺₂, are found however to be larger than previous estimates and to exhibit little dependence on LiH internal vibrational energy. The consequences of such findings on the broader network of early universe reactions involving Li-containing molecules will be discussed from an analysis of these newly obtained quantum reaction rates.

In a thermally bistable medium, cold, dense gas is separated from warm, rarefied gas by thin phase transition layers, or fronts, in which heating, radiative cooling, thermal conduction, and convection of material are balanced. We calculate the steady-state structure of such fronts in the presence of magnetic fields, including the processes of ion–neutral drift and ion–neutral frictional heating. We find that ambipolar diffusion efficiently transports the magnetic field across the fronts, leading to a flat magnetic field strength profile. The thermal profiles of such fronts are not significantly different from those of unmagnetized fronts. The near uniformity of the magnetic field strength across a front is consistent with the flat field strength–gas density relation that is observed in diffuse interstellar gas.

We present Spitzer measurements of the aromatic (also known as polycyclic aromatic hydrocarbon) features for 35 Seyfert galaxies from the revised Shapley–Ames sample and find that the relative strengths of the features differ significantly from those observed in star-forming galaxies. Specifically, the features at 6.2, 7.7, and 8.6 μm are suppressed relative to the 11.3 μm feature in Seyferts. Furthermore, we find an anti-correlation between the L(7.7 μm)/L(11.3 μm) ratio and the strength of the rotational H₂ emission, which traces shocked gas. This suggests that shocks suppress the short-wavelength features by modifying the structure of the aromatic molecules or destroying the smallest grains. Most Seyfert nuclei fall on the relationship between aromatic emission and [Ne ii] emission for star-forming galaxies, indicating that aromatic-based estimates of the star formation rate are generally reasonable in galaxies hosting active galactic nuclei. For the outliers from this relationship, which have small L(7.7 μm)/L(11.3 μm) ratios and strong H₂ emission, the 11.3 μm feature still provides a valid measure of the star formation rate.

This work presents a homogeneous determination of lithium abundances in a large sample of giant-planet-hosting stars (N = 117) and a control sample of disk stars without detected planets (N = 145). The lithium abundances were derived using a detailed profile fitting of the Li i doublet at 6708 Å in LTE. The planet-hosting and comparison stars were chosen to have significant overlap in their respective physical properties, including effective temperatures, luminosities, masses, metallicities, and ages. The combination of uniform data and homogeneous analysis with well-selected samples makes this study well suited to probe for possible differences in the lithium abundances found in planet-hosting stars. An overall comparison between the two samples reveals no obvious differences between stars with and without planets. A closer examination of the behavior of the Li abundances over a narrow range of effective temperature (5700 K ⩽ T_eff ⩽ 5850 K) indicates subtle differences between the two stellar samples; this temperature range is particularly sensitive to various physical processes that can deplete lithium. In this T_eff range, planet-hosting stars have lower Li abundances (by ∼0.26 dex on average) than the comparison stars, although this segregation may be influenced by combining stars from a range of ages, metallicities, and masses. When stars with very restricted ranges in metallicity ([Fe/H] = 0.00 to +0.20 dex) and mass (M ∼ 1.05–1.15 M_☉) are compared, however, both stars with and without planets exhibit similar behaviors in the lithium abundance with stellar age, suggesting that there are no differences in the lithium abundances between stars with planets and stars not known to have planets.

We aim to investigate the magnetic field strengths and cyclotron emission of the two soft X-ray-emitting intermediate polars (IPs) UU Col and NY Lup. We study the connection between polars and soft X-ray-emitting IPs by searching for evidence of circularly polarized light in these two systems, which may be examples of progenitors of polars. We carried out photopolarimetric observations of our targets using the Very Large Telescope (UT2) and FORS1 at Paranal. Imaging polarimetry with good signal-to-noise and relatively high time resolution is possible for these targets using such a large telescope. Detection of circular polarization, modulated according to a white dwarf (WD) spin period, is clear evidence of cyclotron emission processes near the WD surface. The color dependence of the polarization allows us to make estimates of the magnetic field strength. We found that both UU Col and NY Lup emit circularly polarized light in the B and I bands, modulated at the spin period of the WD in each case. We add further confirmation to the idea that soft X-ray-emitting IPs emit circularly polarized light and that cyclotron emission plays an important role in these systems. This also suggests that some soft X-ray-emitting IPs might be progenitors of polars.

We studied the spatial dynamics of the flaring loop in the 2005 August 22 event using microwave (NoRH) and hard X-ray (RHESSI) observations together with complementary data from SOHO/MDI, SMART at Hida, SOHO/EIT, and TRACE. We have found that (1) the pre-flare morphology of the active region exhibits a strongly sheared arcade seen in Hα and the J-shape filament seen in EUV; (2) energy release and high-energy electron acceleration occur in a sequence along the extensive arcade; (3) the shear angle and the parallel (to the magnetic neutral line) component of the footpoint (FP) distance steadily decrease during the flare process; (4) the radio loop shrinks in length and height during the first emission peak, and later it grows; after the fourth peak the simultaneous descending of the brightest loop and formation of a new microwave loop at a higher altitude occur; (5) the hard X-ray coronal source is located higher than the microwave loop apex and shows faster upward motion; (6) the first peak on microwave time profiles is present in both the loop top and FP regions. However, the emission peaks that follow are present only in the FP regions. We conclude that after the first emission peak the acceleration site is located over the flaring arcade and particles are accelerated along magnetic field lines. We make use of the collapsing magnetic trap model to understand some observational effects.

The logarithmic differential star count of the Two Micron All Sky Survey in K_s band can be well approximated by a single power-law luminosity function. With a fiducial Galactic structure, we measure the luminosity function for the entire Milky Way. The distribution of the power-law index is roughly isotropic and shows no obvious trend with the Galactic latitude. The value for the power-law index, the bright and the faint ends of the luminosity function are 1.85 ± 0.035, K_s = −7.86 ± 0.60 mag, and K_s = 6.88 ± 0.66 mag, respectively. Our result strongly supports the notion of a universal luminosity function in our Galaxy. We also find that the luminosity function of LMC/SMC is similar to that of the Milky Way.

First generation space-based optical coronagraphic telescopes will obtain images of cool gas- and ice-giant exoplanets around nearby stars. Exoplanets lying at planet–star separations larger than about 1 AU—where an exoplanet can be resolved from its parent star—have spectra that are dominated by reflected light to beyond 1 μm and punctuated by molecular absorption features. Here, we consider how exoplanet albedo spectra and colors vary as a function of planet–star separation, metallicity, mass, and observed phase for Jupiter and Neptune analogs from 0.35 to 1 μm. We model Jupiter analogs with 1× and 3× the solar abundance of heavy elements, and Neptune analogs with 10× and 30× the solar abundance of heavy elements. Our model planets orbit a solar analog parent star at separations of 0.8 AU, 2 AU, 5 AU, and 10 AU. We use a radiative–convective model to compute temperature–pressure profiles. The giant exoplanets are found to be cloud-free at 0.8 AU, possess H₂O clouds at 2 AU, and have both NH₃ and H₂O clouds at 5 AU and 10 AU. For each model planet we compute moderate resolution (R = λ/Δλ ∼ 800) albedo spectra as a function of phase. We also consider low-resolution spectra and colors that are more consistent with the capabilities of early direct imaging capabilities. As expected, the presence and vertical structure of clouds strongly influence the albedo spectra since cloud particles not only affect optical depth but also have highly directional scattering properties. Observations at different phases also probe different volumes of atmosphere as the source–observer geometry changes. Because the images of the planets themselves will be unresolved, their phase will not necessarily be immediately obvious, and multiple observations will be needed to discriminate between the effects of planet–star separation, metallicity, and phase on the observed albedo spectra. We consider the range of these combined effects on spectra and colors. For example, we find that the spectral influence of clouds depends more on planet–star separation and hence atmospheric temperature than metallicity, and it is easier to discriminate between cloudy 1× and 3× Jupiters than between 10× and 30× Neptunes. In addition to alkalis and methane, our Jupiter models show H₂O absorption features near 0.94 μm. While solar system giant planets are well separated by their broadband colors, we find that arbitrary giant exoplanets can have a large range of possible colors and that color alone cannot be relied upon to characterize planet types. We also predict that giant exoplanets receiving greater insolation than Jupiter will exhibit higher equator-to-pole temperature gradients than are found on Jupiter and thus may exhibit differing atmospheric dynamics. These results are useful for future interpretation of direct imaging exoplanet observations as well as for deriving requirements and designing filters for optical direct imaging instrumentation.

Low-resolution, mid-infrared Spitzer/IRS spectral maps are presented for three nearby, low-metallicity dwarf galaxies (NGC 55, NGC 3109, and IC 5152) for the purpose of examining the spatial distribution and variation of polycyclic aromatic hydrocarbon (PAH) emission. The sample straddles a metallicity of 12 + log(O/H) ≈ 8, a transition point below which PAH intensity empirically drops and the character of the interstellar medium changes. We derive quantitative radiances of PAH features and atomic lines on both global and spatially resolved scales. The Spitzer spectra, combined with extensive ancillary data from the UV through the mid-infrared, allow us to examine changes in the physical environments and in PAH feature radiances down to a physical scale of ∼50 pc. We discuss correlations between various PAH emission feature and atomic line radiances. The (6.2 μm)/(11.3 μm), (7.7 μm)/(11.3 μm), (8.6 μm)/(11.3 μm), (7.7 μm)/(6.2 μm), and (8.6 μm)/(6.2 μm) PAH radiance ratios are found to be independent of position across all three galaxies, although the ratios do vary from galaxy to galaxy. As seen in other galaxies, we find no variation in the grain size distribution as a function of local radiation field strength. Absolute PAH feature intensities as measured by a ratio of PAH/(24 μm) radiances are seen to vary both positionally within a given galaxy and from one galaxy to another when integrated over the full observed extent of each system. We examine direct comparisons of CC mode PAH ratios (7.7 μm)/(6.2 μm) and (8.6 μm)/(6.2 μm) to the mixed (CC/CH) mode PAH ratio (7.7 μm)/(11.3 μm). We find little variation in either mode and no difference in trends between modes. While the local conditions change markedly over the observed regions of these galaxies, the properties of PAH emission show a remarkable degree of uniformity.

We analyze subarcsecond resolution interferometric CO line data for 12 submillimeter-luminous (S_850 μm ⩾ 5 mJy) galaxies with redshifts between 1 and 3, presenting new data for 4 of them. Morphologically and kinematically, most of the 12 systems appear to be major mergers. Five of them are well-resolved binary systems, and seven are compact or poorly resolved. Of the four binary systems for which mass measurements for both separate components can be made, all have mass ratios of 1:3 or closer. Furthermore, comparison of the ratio of compact to binary systems with that observed in local ULIRGs indicates that at least a significant fraction of the compact submillimeter-luminous galaxies (SMGs) must also be late-stage mergers. In addition, the dynamical and gas masses we derive are most consistent with the lower end of the range of stellar masses published for these systems, favoring cosmological models in which SMGs result from mergers. These results all point to the same conclusion that most of the bright SMGs with L_IR ≳ 5 × 10¹² L_☉ are likely major mergers.

We present a set of cosmological simulations with radiative transfer in order to model the reionization history of the universe from z = 18 down to z = 6. Galaxy formation and the associated star formation are followed self-consistently with gas and dark matter dynamics using the RAMSES code, while radiative transfer is performed as a post-processing step using a moment-based method with the M1 closure relation in the ATON code. The latter has been ported to a multiple Graphics Processing Unit (GPU) architecture using the CUDA language together with the MPI library, resulting in an overall acceleration that allows us to tackle radiative transfer problems at a significantly higher resolution than previously reported: 1024³ + 2 levels of refinement for the hydrodynamic adaptive grid and 1024³ for the radiative transfer Cartesian grid. We reach a typical acceleration factor close to 100× when compared to the CPU version, allowing us to perform 1/4 million time steps in less than 3000 GPU hr. We observe good convergence properties between our different resolution runs for various volume- and mass-averaged quantities such as neutral fraction, UV background, and Thomson optical depth, as long as the effects of finite resolution on the star formation history are properly taken into account. We also show that the neutral fraction depends on the total mass density, in a way close to the predictions of photoionization equilibrium, as long as the effect of self-shielding are included in the background radiation model. Although our simulation suite has reached unprecedented mass and spatial resolution, we still fail in reproducing the z ∼ 6 constraints on the neutral fraction of hydrogen and the intensity of the UV background. In order to account for unresolved density fluctuations, we have modified our chemistry solver with a simple clumping factor model. Using our most spatially resolved simulation (12.5 Mpc h⁻¹ with 1024³ particles) to calibrate our subgrid model, we have resimulated our largest box (100 Mpc h⁻¹ with 1024³ particles) with the modified chemistry, successfully reproducing the observed level of neutral hydrogen in the spectra of high-redshift quasars. We however did not reproduce the average photoionization rate inferred from the same observations. We argue that this discrepancy could be partly explained by the fact that the average radiation intensity and the average neutral fraction depend on different regions of the gas density distribution, so that one quantity cannot be simply deduced from the other.

We present deep optical integral-field spectroscopic observations of the nearby (z ∼ 0.01) brightest cluster galaxy NGC 4696 in the core of the Centaurus Cluster, made with the Wide Field Spectrograph on the Australian National University 2.3 m telescope at Siding Spring Observatory. We investigate the morphology, kinematics, and excitation of the emission-line filaments and discuss these in the context of a model of a minor merger. We suggest that the emission-line filaments in this object have their origin in the accretion of a gas-rich galaxy and that they are excited by v ∼ 100–200 km s⁻¹  shocks driven into the cool filament gas by the ram pressure of the transonic passage of the merging system through the hot halo gas of NGC 4696.

The statistical meaning of the local non-Gaussianity parameters f_NL and g_NL is examined in detail. Their relations to the skewness and the kurtosis of the initial distribution are shown to obey simple fitting formulae, accurate on galaxy–cluster scales. We argue that the knowledge of f_NL and g_NL is insufficient for reconstructing a well-defined distribution of primordial fluctuations. Requiring the reconstructed probability density function (pdf) to be positive enforces a theoretical lower bound g_NL ≳ −1.2 × 10⁵, competitive with the observational bounds in the current literature. By weakening the statistical significance of f_NL and g_NL, it is possible to reconstruct a well-defined pdf by using a truncated Edgeworth series. We give some general guidelines on the use of such a series, noting in particular that (1) the Edgeworth series cannot represent models with nonzero f_NL, unless g_NL is nonzero, and also (2) the series cannot represent models with g_NL < 0, unless some higher-order non-Gaussianities are known. Finally, we apply the Edgeworth series to calculate the effects of g_NL on the abundances of massive clusters and large voids. We show that the abundance of voids may generally be more sensitive to high-order non-Gaussianities than the cluster abundance.

We present the recently updated and expanded MASSCLEANcolors, a database of 70 million Monte Carlo models selected to match the properties (metallicity, ages, and masses) of stellar clusters found in the Large Magellanic Cloud (LMC). This database shows the rather extreme and non-Gaussian distribution of integrated colors and magnitudes expected with different cluster age and mass and the enormous age degeneracy of integrated colors when mass is unknown. This degeneracy could lead to catastrophic failures in estimating age with standard simple stellar population models, particularly if most of the clusters are of intermediate or low mass, like in the LMC. Utilizing the MASSCLEANcolors database, we have developed MASSCLEANage, a statistical inference package which assigns the most likely age and mass (solved simultaneously) to a cluster based only on its integrated broadband photometric properties. Finally, we use MASSCLEANage to derive the age and mass of LMC clusters based on integrated photometry alone. First, we compare our cluster ages against those obtained for the same seven clusters using more accurate integrated spectroscopy. We find improved agreement with the integrated spectroscopy ages over the original photometric ages. A close examination of our results demonstrates the necessity of solving simultaneously for mass and age to reduce degeneracies in the cluster ages derived via integrated colors. We then selected an additional subset of 30 photometric clusters with previously well-constrained ages and independently derive their age using the MASSCLEANage with the same photometry with very good agreement. The MASSCLEANage program is freely available under GNU General Public License.

HD 259440 is a B0pe star that was proposed as the optical counterpart to the γ-ray source HESS J0632+057. Here, we present optical spectra of HD 259440 acquired to investigate the stellar parameters, the properties of the Be star disk, and evidence of binarity in this system. Emission from the Hα line shows evidence of a spiral density wave in the nearly edge-on disk. We find a best-fit stellar effective temperature of 27,500–30,000 K and a log surface gravity of 3.75–4.0, although our fits are somewhat ambiguous due to scattered light from the circumstellar disk. We derive a mass of 13.2–19.0 M_☉ and a radius of 6.0–9.6 R_☉. By fitting the spectral energy distribution, we find a distance between 1.1 and 1.7 kpc. We do not detect any significant radial velocity shifts in our data, ruling out orbital periods shorter than one month. If HD 259440 is a binary, it is likely a long-period (>100 d) system.

Hot Jupiter atmospheres exhibit fast, weakly ionized winds. The interaction of these winds with the planetary magnetic field generates drag on the winds and leads to ohmic dissipation of the induced electric currents. We study the magnitude of ohmic dissipation in representative, three-dimensional atmospheric circulation models of the hot Jupiter HD 209458b. We find that ohmic dissipation can reach or exceed 1% of the stellar insolation power in the deepest atmospheric layers, in models with and without dragged winds. Such power, dissipated in the deep atmosphere, appears sufficient to slow down planetary contraction and explain the typically inflated radii of hot Jupiters. This atmospheric scenario does not require a top insulating layer or radial currents that penetrate deep in the planetary interior. Circulation in the deepest atmospheric layers may actually be driven by spatially non-uniform ohmic dissipation. A consistent treatment of magnetic drag and ohmic dissipation is required to further elucidate the consequences of magnetic effects for the atmospheres and the contracting interiors of hot Jupiters.

We present a new analysis of the motion of pressure-confined, broad-line region (BLR) clouds in active galactic nuclei (AGNs) taking into account the combined influence of gravity and radiation pressure. We calculate cloud orbits under a large range of conditions and include the effect of column density variation as a function of location. The dependence of radiation pressure force on the level of ionization and the column density are accurately computed. The main results are as follows. (1) The mean cloud locations (r_BLR) and line widths (FWHMs) are combined in such a way that the simple virial mass estimate, r_BLR, FWHM²/G, gives a reasonable approximation to M_BH even when radiation pressure force is important. The reason is that L/M rather than L is the main parameter affecting the planar cloud motion. (2) Reproducing the mean observed r_BLR, FWHM, and line intensity of Hβ and C iv λ1549 requires at least two different populations of clouds. (3) The cloud location is a function of both L^1/2 and L/M. Given this, we suggest a new approximation for r_BLR which, when inserted into the BH mass equation, results in a new approximation for M_BH. The new expression involves L^1/2, FWHM, and two constants that are obtained from a comparison with available M–σ* mass estimates. It deviates only slightly from the old mass estimate at all luminosities. (4) The quality of the present black hole mass estimators depends, critically, on the way the present M–σ* AGN sample (29 objects) represents the overall population, in particular the distribution of L/L_Edd.

Measurement of the chemical and isotopic composition of cosmic rays is essential for the precise understanding of their propagation in the galaxy. While the model parameters are mainly determined using the B/C ratio, the study of extended sets of ratios can provide stronger constraints on the propagation models. In this paper, the relative abundances of light-nuclei lithium, beryllium, boron, and carbon are presented. The secondary-to-primary ratios Li/C, Be/C, and B/C have been measured in the kinetic energy range 0.35–45 GeV nucleon⁻¹. The isotopic ratio ⁷Li/⁶Li is also determined in the magnetic rigidity interval 2.5–6.3 GV. The secondary-to-secondary ratios Li/Be, Li/B, and Be/B are also reported. These measurements are based on the data collected by the Alpha Magnetic Spectrometer AMS-01 during the STS-91 space shuttle flight in 1998 June. Our experimental results are in substantial agreement with other measurements, where they exist. We describe our light-nuclei data with a diffusive-reacceleration model. A 10%–15% overproduction of Be is found in the model predictions and can be attributed to uncertainties in the production cross-section data.

The evolution and explosion of metal-free stars with masses 10–100 M_☉ are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7 ⩽ Z ⩽ 13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z] ≲ −3. The amount of ionizing radiation from this generation of stars is ∼2.16 MeV per baryon (4.15 B per M_☉; where 1 B = 1 Bethe = 10⁵¹ erg) for a Salpeter IMF, and may have played a role in reionizing the universe. Neglecting rotation, most of the stars end their lives as blue supergiants and form supernovae with distinctive light curves resembling SN 1987A, but some produce primary nitrogen due to dredge-up and become red supergiants. These make brighter supernovae like typical Type IIp's. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20–30 M_☉, with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of ∼40 M_☉. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In contrast, explosion energies somewhat less than 1.2 B seem to be preferred in most cases.

We find a unique direction in the cosmic microwave background sky around which giant rings have an anomalous mean temperature profile. This direction is in very close alignment with the afore measured anomalously large bulk flow direction. Using Monte Carlo simulations, we estimate the significance of the giant rings at the 3σ level and the alignment with the bulk flow at 2.5σ. We argue that a cosmic defect seeded by a pre-inflationary particle could explain the giant rings, the large bulk flow, and their alignment.

LS I +61 303 is an exceptionally rare example of a high-mass X-ray binary that also exhibits MeV–TeV emission, making it one of only a handful of "γ-ray binaries." Here we present Hα spectra that show strong variability during the 26.5 day orbital period and over decadal timescales. We detect evidence of a spiral density wave in the Be circumstellar disk over part of the orbit. The Hα line profile also exhibits a dramatic emission burst shortly before apastron, observed as a redshifted shoulder in the line profile, as the compact source moves almost directly away from the observer. We investigate several possible origins for this red shoulder, including an accretion disk, mass-transfer stream, and a compact pulsar wind nebula that forms via a shock between the Be star's wind and the relativistic pulsar wind.

More than 50% of active galactic nuclei (AGNs) are suspected to be red and affected by dust obscuration. Meanwhile, popular spectral diagnostics of AGNs are based on optical or ultraviolet light, making dust obscuration the primary concern for understanding the general nature of AGNs and the supermassive black holes residing in them. To provide a method for investigating properties of dusty AGNs, we derive new black hole (BH) mass estimators based on velocity widths and luminosities of near-infrared (NIR) hydrogen emission lines such as Pα and Pβ, and also investigate the line ratios of these hydrogen lines. To derive the BH mass (M_BH) estimators, we used a sample of 37 unobscured type 1 AGNs with an M_BH range of 10^6.8–10^9.4 M_☉, where M_BH comes from either the reverberation mapping method or single-epoch measurement method using Balmer lines. Our work shows that M_BH can be estimated from the Paschen line luminosities and velocity widths to an accuracy of 0.18–0.24 dex (rms scatter). We also show that the mean line ratios of the Paschen lines and the Balmer lines are $\mathrm{\frac{H\alpha }{P\alpha }} \simeq 9.00$, $\mathrm{\frac{H\beta }{P\alpha }} \simeq 2.70$, which are consistent with case B recombination under a typical AGN broad-line region (BLR) environment. These ratios can be used as reference points when estimating the amount of dust extinction over the BLR for red AGNs. We expect the future application of the new BH mass estimators on red, dusty AGNs to provide a fresh view of obscured AGNs.

We investigate the feasibility of extracting the gravitational nanolensing signal due to the presence of subsolar mass halos within galaxy-sized dark matter halos. We show that subsolar mass halos in a lensing galaxy can cause strong nanolensing events with shorter durations and smaller amplitudes than microlensing events caused by stars. We develop techniques that can be used in future surveys such as Pan-STARRS, LSST, and OMEGA to search for the nanolensing signal from subsolar mass halos.

Collective transverse coronal loop oscillations seem to be detected in observational studies. In this regard, Luna et al. modeled the collective kink-like normal modes of several cylindrical loop systems using the T-matrix theory. This paper investigates the effects of longitudinal density stratification along the loop axis on the collective kink-like modes of the system of coronal loops. The coronal loop system is modeled as cylinders of parallel flux tubes, with two ends of each loop at the dense photosphere. The flux tubes are considered as uniform magnetic fields, with stratified density along the loop axis which changes discontinuously at the lateral surface of each cylinder. The MHD equations are reduced to solve a set of two coupled dispersion relations for frequencies and wavenumbers, in the presence of a stratification parameter. The fundamental and first overtone frequencies and longitudinal wavenumbers are computed. The previous results are verified for an unstratified coronal loop system. Finally, we conclude that an increased longitudinal density stratification parameter will result in an increase of the frequencies. The frequency ratios, first overtones to fundamentals, are very sensitive functions of the density scale height parameter. Therefore, stratification should be included in dynamics of coronal loop systems. For unstratified coronal loop systems, these ratios are the same as monoloop ones.

Recent theoretical and observational studies have shown that ashes from thermonuclear burning may be ejected during radius-expansion bursts, giving rise to photoionization edges in the X-ray spectra. We report a search for such features in Chandra spectra observed from the low-mass X-ray binary 4U 1728−34. We analyzed the spectra from four radius-expansion bursts detected in 2006 July, and two in 2002 March, but found no evidence for discrete features. We estimate upper limits for the equivalent widths of edges of a few hundred eV, which for the moderate temperatures observed during the bursts, are comparable with the predictions. During the 2006 July observation 4U 1728−34 exhibited weak, unusually frequent bursts (separated by <2 hr in some cases), with profiles and α-values characteristic of hydrogen-poor fuel. Recurrence times as short as those measured are insufficient to exhaust the accreted hydrogen at solar composition, suggesting that the source accretes hydrogen deficient fuel, for example, from an evolved donor. The detection for the first time of a 10.77 minute periodic signal in the persistent intensity, perhaps arising from orbital modulation, supports this explanation and suggests that this system is an ultracompact binary similar to 4U 1820−30.

We use the deepest and the most comprehensive photometric data currently available for GOODS-South (GOODS-S) galaxies to measure their photometric redshifts. The photometry includes VLT/VIMOS (U band), HST/ACS (F435W, F606W, F775W, and F850LP bands), VLT/ISAAC (J, H, and K_s bands), and four Spitzer/IRAC channels (3.6, 4.5, 5.8, and 8.0 μm). The catalog is selected in the z band (F850LP) and photometry in each band is carried out using the recently completed TFIT algorithm, which performs point-spread function (PSF) matched photometry uniformly across different instruments and filters, despite large variations in PSFs and pixel scales. Photometric redshifts are derived using the GOODZ code, which is based on the template fitting method using priors. The code also implements "training" of the template spectral energy distribution (SED) set, using available spectroscopic redshifts in order to minimize systematic differences between the templates and the SEDs of the observed galaxies. Our final catalog covers an area of 153 arcmin² and includes photometric redshifts for a total of 32,505 objects. The scatter between our estimated photometric and spectroscopic redshifts is σ = 0.040 with 3.7% outliers to the full z-band depth of our catalog, decreasing to σ = 0.039 and 2.1% outliers at a magnitude limit m_z< 24.5. This is consistent with the best results previously published for GOODS-S galaxies, however, the present catalog is the deepest yet available and provides photometric redshifts for significantly more objects to deeper flux limits and higher redshifts than earlier works. Furthermore, we show that the photometric redshifts estimated here for galaxies selected as dropouts are consistent with those expected based on the Lyman break technique.

We analyze the physical processes of gap formation in an inviscid protoplanetary disk with an embedded protoplanet using a two-dimensional local shearing-sheet model. The spiral density wave launched by the planet shocks and the angular momentum carried by the wave is transferred to the background flow. The exchange of the angular momentum can affect the mass flux in the vicinity of the planet to form an underdense region, or gap, around the planetary orbit. We first perform weakly nonlinear analyses to show that the specific vorticity formed by shock dissipation of the density wave can be a source of mass flux in the vicinity of the planet and that the gap can be opened even for low-mass planets unless the migration of the planet is substantial. We then perform high-resolution numerical simulations to check analytic consideration. By comparing the gap-opening timescale and type I migration timescale, we propose a criterion for the formation of underdense region around the planetary orbit that is qualitatively different from previous studies. The minimum mass required for the planet to form a dip is twice as small as previous studies if we incorporate the standard values of type I migration timescale, but it can be much smaller if there is a location in the disk where type I migration is halted.

The detection of high contrast companions at small angular separation appears feasible in conventional direct images using the self-calibration properties of interferometric observable quantities. The friendly notion of closure phase, which is key to the recent observational successes of non-redundant aperture masking interferometry used with adaptive optics, appears to be one example of a wide family of observable quantities that are not contaminated by phase noise. In the high-Strehl regime, soon to be available thanks to the coming generation of extreme adaptive optics systems on ground-based telescopes, and already available from space, closure phase like information can be extracted from any direct image, even taken with a redundant aperture. These new phase-noise immune observable quantities, called kernel phases, are determined a priori from the knowledge of the geometry of the pupil only. Re-analysis of archive data acquired with the Hubble Space Telescope NICMOS instrument using this new kernel-phase algorithm demonstrates the power of the method as it clearly detects and locates with milliarcsecond precision a known companion to a star at angular separation less than the diffraction limit.

Spitzer Infrared Spectrograph data support the interpretation that BP Piscium, a gas and dust enshrouded star residing at high Galactic latitude, is a first-ascent giant rather than a classical T Tauri star. Our analysis suggests that BP Piscium's spectral energy distribution can be modeled as a disk with a gap that is opened by a giant planet. Modeling the rich mid-infrared emission line spectrum indicates that the solid-state emitting grains orbiting BP Piscium are primarily composed of ∼75 K crystalline, magnesium-rich olivine; ∼75 K crystalline, magnesium-rich pyroxene; ∼200 K amorphous, magnesium-rich pyroxene; and ∼200 K annealed silica (cristobalite). These dust grains are all sub-micron sized. The giant planet and gap model also naturally explains the location and mineralogy of the small dust grains in the disk. Disk shocks that result from disk–planet interaction generate the highly crystalline dust which is subsequently blown out of the disk mid-plane and into the disk atmosphere.

We present light curves of three classical novae (CNe; KT Eridani, V598 Puppis, V1280 Scorpii) and one recurrent nova (RS Ophiuchi) derived from data obtained by the Solar Mass Ejection Imager (SMEI) on board the Coriolis satellite. SMEI provides near complete skymap coverage with precision visible-light photometry at 102 minute cadence. The light curves derived from these skymaps offer unprecedented temporal resolution around, and especially before, maximum light, a phase of the eruption normally not covered by ground-based observations. They allow us to explore fundamental parameters of individual objects including the epoch of the initial explosion, the reality and duration of any pre-maximum halt (found in all three fast novae in our sample), the presence of secondary maxima, speed of decline of the initial light curve, plus precise timing of the onset of dust formation (in V1280 Sco) leading to estimation of the bolometric luminosity, white dwarf mass, and object distance. For KT Eri, Liverpool Telescope SkyCamT data confirm important features of the SMEI light curve and overall our results add weight to the proposed similarities of this object to recurrent rather than to CNe. In RS Oph, comparison with hard X-ray data from the 2006 outburst implies that the onset of the outburst coincides with extensive high-velocity mass loss. It is also noted that two of the four novae we have detected (V598 Pup and KT Eri) were only discovered by ground-based observers weeks or months after maximum light, yet these novae reached peak magnitudes of 3.46 and 5.42, respectively. This emphasizes the fact that many bright novae per year are still overlooked, particularly those of the very fast speed class. Coupled with its ability to observe novae in detail even when relatively close to the Sun in the sky, we estimate that as many as five novae per year may be detectable by SMEI.

We present new RHESSI upper limits in the 3–200 keV energy range for solar hard X-ray emission in the absence of flares and active regions, i.e., the quiet Sun, using data obtained between 2005 July and 2009 April. These new limits, substantially deeper than any previous ones, constrain several physical processes that could produce hard X-ray emission. These include cosmic-ray effects and the generation of axions within the solar core. The data also limit the properties of  "nanoflares," a leading candidate to explain coronal heating. We find it unlikely for nanoflares involving nonthermal effects to heat the corona because such events would require a steep electron spectrum E^−δ with index δ>5 extending to very low energies (<1 keV), into the thermal energy range. We also use the limits to constrain the parameter space of an isothermal model and coronal thin-target emission models (power-law and kappa distributions).

We present 015 resolution observations of the 227 GHz continuum emission from the circumstellar disk around the FU Orionis star PP 13S*. The data were obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) Paired Antenna Calibration System (C-PACS), which measures and corrects the atmospheric delay fluctuations on the longest baselines of the array in order to improve the sensitivity and angular resolution of the observations. A description of the C-PACS technique and the data reduction procedures are presented. C-PACS was applied to CARMA observations of PP 13S*, which led to a factor of 1.6 increase in the observed peak flux of the source, a 36% reduction in the noise of the image, and a 52% decrease in the measured size of the source major axis. The calibrated complex visibilities were fitted with a theoretical disk model to constrain the disk surface density. The total disk mass from the best-fit model corresponds to 0.06 M_☉, which is larger than the median mass of a disk around a classical T Tauri star. The disk is optically thick at a wavelength of 1.3 mm for orbital radii less than 48 AU. At larger radii, the inferred surface density of the PP 13S* disk is an order of magnitude lower than that needed to develop a gravitational instability.

We investigate the properties and environments of Type Ia Supernova (SN Ia) host galaxies in the Stripe 82 of the Sloan Digital Sky Survey-II Supernova Survey centered on the celestial equator. Host galaxies are defined as the galaxy nearest to the supernova (SN) in terms of angular distance whose velocity difference from the SN is less than 1000 km s⁻¹. Eighty seven SN Ia host galaxies are selected from the SDSS Main galaxy sample with the apparent r-band magnitude m_r < 17.77, and compared with the SDSS Main galaxies. The SN Ia rates for early- and late-type galaxies are 0.81 ± 0.19 SN (100 yr)⁻¹ and 0.99 ± 0.21 SN (100 yr)⁻¹, respectively. We find that the host galaxies have a color distribution consistent with that of the Main galaxies, regardless of their morphology. However, host galaxies are on average brighter than the Main galaxies by ∼0.3 mag over the range of −18.3>M_r > − 21.3. But the brighter ends of their luminosity distributions are similar. The distribution of the distance to the nearest neighbor galaxy shows that SNe Ia are more likely to occur in isolated galaxies without close neighbors. We also find that the SN Ia host galaxies are preferentially located in a region close to massive galaxy clusters compared to the Main galaxies.

We use stellar masses, surface photometry, strong-lensing masses, and stellar velocity dispersions (σ_e/2) to investigate empirical correlations for the definitive sample of 73 early-type galaxies (ETGs) that are strong gravitational lenses from the SLACS survey. The traditional correlations (fundamental plane (FP) and its projections) are consistent with those found for non-lens galaxies, supporting the thesis that SLACS lens galaxies are representative of massive ETGs (dimensional mass M_dim = 10¹¹–10¹² M_☉). The addition of high-precision strong-lensing estimates of the total mass allows us to gain further insights into their internal structure: (1) the average slope of the total mass-density profile ( $\rho _{\rm tot}\propto r^{-\gamma ^{\prime }}$) is 〈γ'〉 = 2.078 ± 0.027 with an intrinsic scatter of 0.16 ± 0.02; (2) γ' correlates with effective radius (r_e) and central mass density, in the sense that denser galaxies have steeper profiles; (3) the dark matter (DM) fraction within r_e/2 is a monotonically increasing function of galaxy mass and size (due to a mass-dependent central cold DM distribution or due to baryonic DM—stellar remnants or low-mass stars—if the initial mass function is non-universal and its normalization increases with mass); (4) the dimensional mass M_dim ≡ 5r_eσ²_e/2/G is proportional to the total (lensing) mass M$_{r_{e}/2}$, and both increase more rapidly than stellar mass M_* (M$_* \propto {M}_{r_{e}/2}^{0.8}$); (5) the mass plane (MP), obtained by replacing surface brightness with surface mass density in the FP, is found to be tighter and closer to the virial relation than the FP and the M_*P, indicating that the scatter of those relations is dominated by stellar population effects; (6) we construct the fundamental hyper-plane by adding stellar masses to the MP and find the M_* coefficient to be consistent with zero and no residual intrinsic scatter. Our results demonstrate that the dynamical structure of ETGs is not scale invariant and that it is fully specified by M$_{r_{e}/2}$, r_e, and σ_e/2. Although the basic trends can be explained qualitatively in terms of varying star formation efficiency as a function of halo mass and as the result of dry and wet mergers, reproducing quantitatively the observed correlations and their tightness may be a significant challenge for galaxy formation models.

The H i 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources (≳1 Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array. We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky model for bright sources, as well as frequency-independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the H i power spectrum. For calibration errors, 0.05% accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, k_⊥ ≳ 0.05 Mpc⁻¹, in the two-dimensional power spectrum.

The so-called hyperquenching technique has been applied to generate water ices containing ammonium and formate ions by sudden freezing of droplets of NH₄Cl, NH₄COOH, and NaCOOH solutions. Salt deposits were obtained after heating the ices to 210 K to sublimate all water content. All stages are controlled by IR transmission spectroscopy. The NH₄⁺ bands are very much broadened and smeared in the frozen droplets, but stand out strongly when water is eliminated. This fact hints toward the difficulty in ascertaining the presence of this species in astrophysical water-containing ices. Vapor-deposited ices of NH₃/HCOOH and H₂O/NH₃/HCOOH mixtures have also been studied for comparison. HCOO⁻ and NH₄⁺ ions are found to be formed in small proportion even at the lowest temperature, 14 K. By thermal processing, their IR bands become stronger, and at 210 K, after water sublimation, they yield IR spectra similar to those obtained from hyperquenched samples. The observations are interpreted in terms of the varying ion arrangement within the solids along the warming process. A direct comparison to laboratory spectra of irradiated samples, as performed by other groups, is not straightforward.

The rapid circularization and synchronization of the stellar components in an eccentric binary system at the onset of Roche lobe overflow is a fundamental assumption common to all binary stellar evolution and population synthesis codes, even though the validity of this assumption is questionable both theoretically and observationally. Here we calculate the evolution of the orbital elements of an eccentric binary through the direct three-body integration of a massive particle ejected through the inner Lagrangian point of the donor star at periastron. The trajectory of this particle leads to three possible outcomes: direct accretion onto the companion star within a single orbit, self-accretion back onto the donor star within a single orbit, or a quasi-periodic orbit around the companion star, possibly leading to the formation of a disk. We calculate the secular evolution of the binary orbit in the first two cases and conclude that direct impact accretion can increase as well as decrease the orbital semimajor axis and eccentricity, while self-accretion always decreases the orbital semimajor axis and eccentricity. In cases where mass overflow contributes to circularizing the orbit, circularization can set in on timescales as short as a few percent of the mass-transfer timescale. In cases where mass overflow increases the eccentricity, the orbital evolution is governed by competition between mass overflow and tidal torques. In the absence of tidal torques, mass overflow results in direct impact can lead to substantially subsynchronously rotating donor stars. Contrary to assumptions common in the literature, direct impact accretion furthermore does not always provide a strong sink of orbital angular momentum in close mass-transferring binaries; in fact, we instead find that a significant part can be returned to the orbit during the particle orbit. The formulation presented in this paper together with our previous work can be combined with stellar and binary evolution codes to generate a better picture of the evolution of eccentric, Roche lobe overflowing binary star systems.

We present new Chandra observations that complete a sample of seventeen (17) luminous infrared galaxies (LIRGs) with D < 60 Mpc and low Galactic column densities of N_H ≲ 5 × 10²⁰ cm⁻². The LIRGs in our sample have total infrared (8–1000 μm) luminosities in the range of L_IR≈ (1–8) × 10¹¹ L_☉. The high-resolution imaging and X-ray spectral information from our Chandra observations allow us to measure separately X-ray contributions from active galactic nuclei and normal galaxy processes (e.g., X-ray binaries and hot gas). We utilized total infrared plus UV luminosities to estimate star formation rates (SFRs) and K-band luminosities and optical colors to estimate stellar masses (M_⋆) for the sample. Under the assumption that the galaxy-wide 2–10 keV luminosity (L^gal_HX) traces the combined emission from high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries, and that the power output from these components is linearly correlated with SFR and M_⋆, respectively, we constrain the relation L^gal_HX = αM_⋆ + βSFR. To achieve this, we construct a Chandra-based data set composed of our new LIRG sample combined with additional samples of less actively star-forming normal galaxies and more powerful LIRGs and ultraluminous infrared galaxies (ULIRGs) from the literature. Using these data, we measure best-fit values of α = (9.05 ± 0.37) × 10²⁸ erg s⁻¹ M⁻¹_☉ and β = (1.62 ± 0.22) × 10³⁹ erg s⁻¹ (M_☉ yr⁻¹)⁻¹. This scaling provides a more physically meaningful estimate of L^gal_HX, with ≈0.1–0.2 dex less scatter, than a direct linear scaling with SFR. Our results suggest that HMXBs dominate the galaxy-wide X-ray emission for galaxies with SFR/M_⋆ ≳5.9 × 10⁻¹¹ yr⁻¹, a factor of ≈2.9 times lower than previous estimates. We find that several of the most powerful LIRGs and ULIRGs, with SFR/M_⋆ ≳ 10⁻⁹ yr⁻¹, appear to be X-ray underluminous with respect to our best-fit relation. We argue that these galaxies are likely to contain X-ray binaries residing in compact star-forming regions that are buried under thick galactic columns large enough to attenuate emission in the 2–10 keV band (N_H ≳ 10²³ cm⁻²).

In 1999, the ChandraX-ray Observatory revealed a 150'' radius halo surrounding the 40'' radius pulsar wind nebula (PWN) G21.5−0.9. A 2005 imaging study of G21.5−0.9 showed that the halo is limb-brightened and suggested that this feature is a candidate for the long-sought supernova remnant (SNR) shell. We present a spectral analysis of SNR G21.5−0.9, using the longest effective observation to date (578.6 ks with the Advanced CCD Imaging Spectrometer (ACIS) and 278.4 ks with the High-Resolution Camera (HRC)) to study unresolved questions about the spectral nature of remnant features, such as the limb brightening of the X-ray halo and the bright knot in the northern part of the halo. The Chandra analysis favors the non-thermal interpretation of the limb. Its spectrum is fit well with a power-law model with a photon index Γ = 2.13 (1.94–2.33) and a luminosity of L_x (0.5–8 keV) = (2.3 ± 0.6) × 10³³ erg s⁻¹ (at an assumed distance of 5.0 kpc). An srcut model was also used to fit the spectrum between the radio and X-ray energies. While the absence of a shell in the radio still prohibits constraining the spectrum at radio wavelengths, we assume a range of spectral indices to infer the 1 GHz flux density and the rolloff frequency of the synchrotron spectrum in X-rays and find that the maximum energy to which electrons are accelerated at the shock ranges from ∼60 to 130 TeV (B/10 μG)^−1/2, where B is the magnetic field in units of μG. For the northern knot, we constrain previous models and find that a two-component power-law (or srcut) + pshock model provides an adequate fit, with the pshock model requiring a very low ionization timescale and solar abundances for Mg and Si. Our spectroscopic study of PSR J1833−1034, the highly energetic pulsar powering G21.5−0.9, shows that its spectrum is dominated by hard non-thermal X-ray emission with some evidence of a thermal component that represents ∼9% of the observed non-thermal emission and that suggests non-standard rapid cooling of the neutron star. Finally, the ACIS and HRC-I images provide the first evidence for variability in the PWN, a property observed in other PWNe such as the Crab and Vela.

The Planck satellite, successfully launched on 2009 May 14 to measure with unprecedented accuracy the primary cosmic microwave background (CMB) anisotropies, is operating as expected. The Standard Model of the Universe ("concordance" model) provides the current realistic context to analyze the CMB and other cosmological/astrophysical data, inflation in the early universe being part of it. The Planck performance for the crucial primordial parameter r, the tensor-to-scalar ratio related to primordial B-mode polarization, will depend on the quality of data analysis and interpretation. The Ginzburg–Landau (G–L) approach to inflation allows us to take high benefit of the CMB data. The fourth-degree double-well inflaton potential gives an excellent fit to the current CMB+LSS data. We evaluate the Planck precision to the recovery of cosmological parameters, taking into account a reasonable toy model for residuals of systematic effects of instrumental and astrophysical origin based on publicly available information. We use and test two relevant models: the ΛCDMr model, i.e., the standard ΛCDM model augmented by r, and the ΛCDMrT model, where the scalar spectral index, n_s, and r are related through the theoretical "banana-shaped" curve r = r(n_s) coming from the G–L theory with a double-well inflaton potential. In the latter case, the analytical expressions for n_s and r are imposed as a hard constraint in a Monte Carlo Markov Chain (MCMC) data analysis. We consider two C_ℓ-likelihoods (with and without B modes) and take into account the white noise sensitivity of Planck (LFI and HFI) in the 70, 100, and 143 GHz channels as well as the residuals from systematic errors and foregrounds. We also consider a cumulative channel of the three mentioned. We produce the sky (mock data) for the CMB multipoles C^TT_l,  C^TE_l,  C^EE_l, and C^BB_l from the ΛCDMr and ΛCDMrT models and obtain the cosmological parameter marginalized likelihood distributions for the two models. Foreground residuals affect only the cosmological parameters sensitive to the B modes. As expected, the likelihood r distribution is more clearly peaked near the fiducial value (r = 0.0427) in the ΛCDMrT model than in the ΛCDMr model. The best value for r in the presence of residuals turns out to be about r ≃ 0.04 for both the ΛCDMr and the ΛCDMrT models. The ΛCDMrT model is very stable; its distributions do not change by including residuals and the B modes. For r we find 0.028 < r < 0.116 at a 95% confidence level (CL) with the best value r = 0.04. We also compute the B mode detection probability by the most sensitive HFI-143 channel. At the level of foreground residual equal to 30% of our toy model, only a 68% CL (1σ) detection is very likely. For a 95% CL detection (2σ), the level of foreground residual should be reduced to 10% or lower of the adopted toy model. The lower bounds (and most probable value) we infer for r support the searching of CMB B-mode polarization in the current data as well as the planned CMB missions oriented toward B polarization.

We present new XMM-Newton measurements of the X-ray luminosities (L_x) and temperatures (T_x) for three clusters of galaxies. Two are low L_x (<3 × 10⁴³ erg s⁻¹) clusters, RXJ0110.3+1938 (z = 0.317) and RXJ1011.0+5339 (z = 0.329). These clusters were selected from the 160 Square Degree Survey, a survey of extended sources serendipitously discovered in pointed ROSAT observations. The third cluster, KDCS 112, was included by chance in one of our pointings, and is an optically selected cluster from the DEEPRANGE survey. It has a similar redshift and X-ray luminosity as the first two. We estimate the optical richness (Λ_cl) of all three clusters. RXJ1011.0+5339 was missed by DEEPRANGE because it is optically poor. However, KDCS112 was missed in the 160SD even though it is brighter in the X-rays than its neighbor RXJ1011.0+5339, because it fell below the 160SD flux limit. The ROSAT flux of RXJ1011.0+5339 was overestimated due to point-source contamination; it is among the lowest luminosity groups with a known X-ray temperature at moderate redshift. These clusters represent a pilot study to probe the L_x–T_x relation at moderate redshifts and low L_x, a regime where feedback processes may increase the scatter or change the mean L_x–T_x relation. The X-ray luminosities and temperatures of the clusters are consistent with the L_x–T_x relationship in galaxy clusters at low redshift, albeit with large scatter. We place a upper limit on the scatter in the L_x–T_x relation of ∼0.1 in δlog T_x for moderate redshift clusters, similar to that of low-redshift clusters.

We investigate the coupling between rock-size solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. In this study, we use three-dimensional radiative hydrodynamic simulations and model solids as a spatial distribution of particles. We assume that half of the total solid fraction is in small grains and half in large solids. The former are perfectly entrained with the gas and set the opacity in the disk, while the latter are allowed to respond to gas drag forces, with the back reaction on the gas taken into account. To explore the maximum effects of gas–solid interactions, we first consider 10 cm size particles. We then compare these results to a simulation with 1 km size particles, which explores the low-drag regime. We show that (1) disk instability planets have the potential to form large cores due to aerodynamic capturing of rock-size solids in spiral arms before fragmentation; (2) temporary clumps can concentrate tens of M_⊕ of solids in very localized regions before clump disruption; (3) the formation of permanent clumps, even in the outer disk, is dependent on the grain-size distribution, i.e., the opacity; (4) nonaxisymmetric structure in the disk can create disk regions that have a solids-to-gas ratio greater than unity; (5) the solid distribution may affect the fragmentation process; (6) proto-gas giants and proto-brown dwarfs can start as differentiated objects prior to the H₂ collapse phase; (7) spiral arms in a gravitationally unstable disk are able to stop the inward drift of rock-size solids, even redistributing them to larger radii; and (8) large solids can form spiral arms that are offset from the gaseous spiral arms. We conclude that planet embryo formation can be strongly affected by the growth of solids during the earliest stages of disk accretion.

We present a detailed study of explosive chromospheric evaporation during a microflare which occurred on 2007 December 7 as observed with the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We find temperature-dependent upflows for lines formed from 1.0 to 2.5 MK and downflows for lines formed from 0.05 to 0.63 MK in the impulsive phase of the flare. Both the line intensity and the nonthermal line width appear enhanced in most of the lines and are temporally correlated with the evaporation velocity. Our results are consistent with the numerical simulations of flare models, which take into account a strong nonthermal electron beam in producing the explosive chromospheric evaporation. The explosive evaporation observed in this microflare implies that the same dynamic processes may exist in events with very different magnitudes.

We use high-resolution Hubble Space Telescope imaging observations of the young (∼15–25 Myr old) star cluster NGC 1818 in the Large Magellanic Cloud to derive an estimate for the binary fraction of F stars (1.3 < M_⋆/M_☉ < 1.6). This study provides the strongest constraints yet on the binary fraction in a young star cluster in a low-metallicity environment ([Fe/H] ∼ −0.4 dex). Employing artificial-star tests, we develop a simple method that can efficiently measure the probabilities of stellar blends and superpositions from the observed stellar catalog. We create synthetic color–magnitude diagrams matching the fundamental parameters of NGC 1818, with different binary fractions and mass-ratio distributions. We find that this method is sensitive to binaries with mass ratios q ≳ 0.4. For binaries with F-star primaries and mass ratios q > 0.4, the binary fraction is ∼0.35. This suggests a total binary fraction for F stars of 0.55 to unity, depending on assumptions about the form of the mass-ratio distribution at low q.

We measure surface brightness fluctuation (SBF) magnitudes in the F814W filter and (g₄₇₅ − I₈₁₄) colors for nine bright early-type Fornax cluster galaxies imaged with the Hubble Space Telescope Advanced Camera for Surveys (ACS). The goal is to achieve the first systematic SBF calibration for the ACS/F814W bandpass. Because of its much higher throughput, F814W is more efficient for SBF studies of distant galaxies than the ACS/F850LP bandpass that has been used to study nearby systems. Over the color range spanned by the sample galaxies, 1.06 < (g₄₇₅ − I₈₁₄) < 1.32 (AB mag), the dependence of SBF magnitude $\overline{m}_{814}$ on (g₄₇₅ − I₈₁₄) is linear to a good approximation, with slope ∼2. When the F850LP SBF distance measurements from the ACS Fornax Cluster Survey are used to derive absolute $\overline{M}_{814}$ magnitudes, the dependence on (g₄₇₅ − I₈₁₄) becomes extremely tight, with a slope of 1.8 ± 0.2 and a scatter of 0.03 mag. The small observed scatter indicates both that the estimated random errors are correct and that the intrinsic deviations from the SBF–color relation are strongly correlated between the F814W and F850LP bandpasses, as expected. The agreement with predictions from stellar population models is good, both in slope and zero point, indicating that our mean Fornax distance of 20 Mpc is accurate. The models predict curvature in the relation beyond the color limits of our sample; thus, the linear calibration should not be extrapolated naively. In the appendices, we reconsider the Tonry ground-based and Jensen NICMOS SBF distance catalogs; we provide a correction formula to ameliorate the small apparent bias in the former and the offset needed to make the latter consistent with other SBF studies. We also tabulate two new SBF distances to galaxies observed in the ACS Virgo Cluster Survey.

We have redetermined the parallax and proper motion of the nearby isolated neutron star RX J185635−3754. We used eight observations with the high-resolution camera of the HST/ACS taken from 2002 through 2004. We performed the astrometric fitting using five independent methods, all of which yielded consistent results. The mean estimate of the parallax, 8.16^+0.9_−0.8 mas (1σ), corresponds to a distance of 123⁺¹¹₋₁₅ pc, in good agreement with our earlier published determination.

Although morphological classification of dwarf galaxies into early and late types can account for some of their origin and characteristics, this does not aid the study of their formation mechanism. Thus an objective classification using principal component analysis together with K means cluster analysis of these dwarf galaxies and their globular clusters (GCs) is carried out to overcome this problem. It is found that the classification of dwarf galaxies in the local volume is irrespective of their morphological indices. The more massive (M_V0 < −13.7) galaxies evolve through self-enrichment and harbor dynamically less evolved younger GCs, whereas fainter galaxies (M_V0 > − 13.7) are influenced by their environment in the star formation process.

In this paper, we investigate the level of star formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of star formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the star formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M_0.8) above an extinction threshold of A_K≈ 0.8 mag, corresponding to a gas surface density threshold of Σ_gas ≈ 116 M_☉ pc². We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H₂) ≈ 10⁴ cm⁻³. Specifically, we find SFR (M_☉ yr⁻¹) = 4.6 ± 2.6 × 10⁻⁸M_0.8 (M_☉) for the clouds in our sample. This relation between the rate of star formation and the amount of dense gas in molecular clouds appears to be in excellent agreement with previous observations of both galactic and extragalactic star-forming activity. It is likely the underlying physical relationship or empirical law that most directly connects star formation activity with interstellar gas over many spatial scales within and between individual galaxies. These results suggest that the key to obtaining a predictive understanding of the SFRs in molecular clouds and galaxies is to understand those physical factors which give rise to the dense components of these clouds.

One of the key predictions of the merger hypothesis for the origin of early-type (elliptical and lenticular) galaxies is that tidally induced asymmetric structure should correlate with signatures of a relatively young stellar population. Such a signature was found by Schweizer & Seitzer at roughly 4σ confidence. In this paper, we revisit this issue with a nearly ten-fold larger sample of 0.01 < z < 0.03 galaxies selected from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We parameterize tidal structure using a repeatable algorithmic measure of asymmetry, and correlate this with color offset from the early-type galaxy color–magnitude relation. We recover the color offset–asymmetry correlation; furthermore, we demonstrate observationally for the first time that this effect is driven by a highly significant trend toward younger ages at higher asymmetry values. We present a simple model for the evolution of early-type galaxies through gas-rich major and minor mergers that reproduces their observed buildup from z = 1 to the present day and the distribution of present-day colors and ages. We show using this model that if both stellar populations and asymmetry were ideal "clocks" measuring the time since last major or minor gas-rich interaction, then we would expect a rather tight correlation between age and asymmetry. We suggest that the source of extra scatter is natural diversity in progenitor star formation history, gas content, and merger mass ratio, but quantitative confirmation of this conjecture will require sophisticated modeling. We conclude that the asymmetry–age correlation is in basic accord with the merger hypothesis, and indicates that an important fraction of the early-type galaxy population is affected by major or minor mergers at cosmologically recent times.

We have measured velocity dispersions (σ) for a sample of 36 galaxies with J < 21.2 or M_r < −20.6 mag in MS 1054-03, a massive cluster of galaxies at z = 0.83. Our data are of uniformly high quality down to our selection limit, our 16 hr exposures typically yielding errors of only δ(σ) ∼ 10% for L* and fainter galaxies. By combining our measurements with data from the literature, we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived sizes, colors and surface brightness. This sample is complete for the typical L^⋆ galaxy at z ∼ 1, unlike most previous z ∼ 1 cluster samples which are complete only for the massive cluster members (>10¹¹ M_☉). We find no evidence for a change in the tilt of the fundamental plane (FP). Nor do we find evidence for evolution in the slope of the color–σ relation and M/L_B–σ relations; measuring evolution at a fixed σ should minimize the impact of structural evolution found in other work. The M/L_B at fixed σ evolves by Δlog₁₀M/L_B = −0.50 ± 0.03 between z = 0.83 and z = 0.02 or dlog₁₀M/L_B = −0.60 ±  0.04 dz, and we find Δ(U − V)_z = −0.24 ±  0.02 mag at fixed σ in the rest frame, matching the expected evolution in M/L_B within 2.25 standard deviations. The implied formation redshift from both the color and M/L_B evolution is z_⋆ = 2.0 ± 0.2 ± 0.3(sys), during the epoch in which the cosmic star formation activity peaked, with the systematic uncertainty showing the dependence of z_⋆ on the assumptions we make about the stellar populations. The lack of evolution in either the tilt of the FP or in the M/L–σ and color–σ relations imply that the formation epoch depends weakly on mass, ranging from z_⋆ = 2.3^+1.3_−0.3 at σ = 300 km s^-1 to z_⋆ = 1.7^+0.3_−0.2 at σ = 160 km s^-1 and implies that the initial mass function similarly varies slowly with galaxy mass.

We determine an expression for the Type I planet migration torque involving a locally isothermal disk, with moderate turbulent viscosity (5 × 10⁻⁴ ≲ α ≲ 0.05), based on three-dimensional nonlinear hydrodynamical simulations. The radial gradients (in a dimensionless logarithmic form) of density and temperature are assumed to be constant near the planet. We find that the torque is roughly equally sensitive to the surface density and temperature radial gradients. Both gradients contribute to inward migration when they are negative. Our results indicate that two-dimensional calculations with a smoothed planet potential, used to account for the effects of the third dimension, do not accurately determine the effects of density and temperature gradients on the three-dimensional torque. The results suggest that substantially slowing or stopping planet migration by means of changes in disk opacity or shadowing is difficult and appears unlikely for a disk that is locally isothermal. The scalings of the torque and torque density with planet mass and gas sound speed follow the expectations of linear theory. We also determine an improved formula for the torque density distribution that can be used in one-dimensional long-term evolution studies of planets embedded in locally isothermal disks. This formula can be also applied in the presence of mildly varying radial gradients and of planets that open gaps. We illustrate its use in the case of migrating super-Earths and determine some conditions sufficient for survival.

We have obtained spectrophotometric observations of 41 anticenter planetary nebulae (PNe) located in the disk of the Milky Way. Electron temperatures and densities, as well as chemical abundances for He, N, O, Ne, S, Cl, and Ar were determined. Incorporating these results into our existing database of PN abundances yielded a sample of 124 well-observed objects with homogeneously determined abundances extending from 0.9 to 21 kpc in galactocentric distance. We performed a detailed regression analysis which accounted for uncertainties in both oxygen abundances and radial distances in order to establish the metallicity gradient across the disk to be 12 + log(O/H) = (9.09 ± 0.05) − (0.058 ± 0.006) × R_g, with R_g in kpc. While we see some evidence that the gradient steepens at large galactocentric distances, more objects toward the anticenter need to be observed in order to confidently establish the true form of the metallicity gradient. We find no compelling evidence that the gradient differs between Peimbert Types I and II, nor is oxygen abundance related to the vertical distance from the galactic plane. Our gradient agrees well with analogous results for H ii regions but is steeper than the one recently published by Stanghellini & Haywood over a similar range in galactocentric distance. A second analysis using PN distances from a different source implied a flatter gradient, and we suggest that we have reached a confusion limit which can only be resolved with greatly improved distance measurements and an understanding of the natural scatter in oxygen abundances.

We have compiled a sample of 14 of the optically brightest radio-quiet quasars (m_i ⩽ 17.5 and z ⩾ 1.9) in the Sloan Digital Sky Survey Data Release 5 quasar catalog that have C iv mini-broad absorption lines (mini-BALs) present in their spectra. X-ray data for 12 of the objects were obtained via a Chandra snapshot survey using ACIS-S, while data for the other two quasars were obtained from archival XMM-Newton observations. Joint X-ray spectral analysis shows that the mini-BAL quasars have a similar average power-law photon index (Γ ≈ 1.9) and level of intrinsic absorption (N_H ≲ 8 × 10²¹ cm⁻²) as non-BMB (neither BAL nor mini-BAL) quasars. Mini-BAL quasars are more similar to non-BMB quasars than to BAL quasars in their distribution of relative X-ray brightness (assessed with Δα_ox). Relative colors indicate mild dust reddening in the optical spectra of mini-BAL quasars. Significant correlations between Δα_ox and UV absorption properties are confirmed for a sample of 56 sources combining mini-BAL and BAL quasars with high signal-to-noise ratio rest-frame UV spectra, which generally supports models in which X-ray absorption is important in enabling driving of the UV absorption-line wind. We also propose alternative parameterizations of the UV absorption properties of mini-BAL and BAL quasars, which may better describe the broad absorption troughs in some respects.

We extend the Unified Radio Catalog, a catalog of sources detected by various (NVSS, FIRST, WENSS, GB6) radio surveys, and SDSS, to IR wavelengths by matching it to the IRAS Point and Faint Source catalogs. By fitting each NVSS-selected galaxy's NUV-NIR spectral energy distribution (SED) with stellar population synthesis models we add to the catalog star formation rates (SFRs), stellar masses, and attenuations. We further add information about optical emission-line properties for NVSS-selected galaxies with available SDSS spectroscopy. Using an NVSS 20 cm (F_1.4 GHz ≳ 2.5 mJy) selected sample, matched to the SDSS spectroscopic ("main" galaxy and quasar) catalogs and IRAS data (0.04 < z ≲ 0.2) we perform an in-depth analysis of the radio–FIR correlation for various types of galaxies, separated into (1) quasars, (2) star-forming, (3) composite, (4) Seyfert, (5) LINER, and (6) absorption line galaxies using the standard optical spectroscopic diagnostic tools. We utilize SED-based SFRs to independently quantify the source of radio and FIR emission in our galaxies. Our results show that Seyfert galaxies have FIR/radio ratios lower than, but still within the scatter of, the canonical value due to an additional (likely active galactic nucleus (AGN)) contribution to their radio continuum emission. Furthermore, IR-detected absorption and LINER galaxies are on average strongly dominated by AGN activity in both their FIR and radio emission; however their average FIR/radio ratio is consistent with that expected for star-forming galaxies. In summary, we find that most AGN-containing galaxies in our NVSS–IRAS–SDSS sample have FIR/radio flux ratios indistinguishable from those of the star-forming galaxies that define the radio–FIR correlation. Thus, attempts to separate AGNs from star-forming galaxies by their FIR/radio flux ratios alone can separate only a small fraction of the AGNs, such as the radio-loud quasars.

We derive the Mg/H ratio in the Orion nebula and in 30 Doradus. We also derive the O/H and the Fe/O ratios in the extremely metal-poor galaxy SBS 0335−052 E. We estimate the dust depletions of Mg, Si, and Fe in Galactic and extragalactic H ii regions. From these depletions we estimate the fraction of O atoms embedded in dust as a function of the O/H ratio. We find an increasing depletion of O with increasing O/H. The O depletion increases from about 0.08 dex, for the metal poorest H ii regions known, to about 0.12 dex, for metal-rich H ii regions. This depletion has to be considered to compare nebular with stellar abundances.

We present the results of an extensive survey of RR Lyrae (RRL) stars in three fields along the major axis of the Triangulum Galaxy (M33). From images taken with the Advanced Camera for Surveys (ACS) Wide Field Channel on board the Hubble Space Telescope through two passbands (F606W and F814W), we have identified and characterized a total of 119 RRL variables (96 RRab (RR0) and 23 RRc (RR1)) in M33. Using the properties of 83 RRL stars (65 RRab and 18 RRc) in the innermost ACS field (hereafter DISK2), we find mean periods of 〈P_ab〉 = 0.553 ± 0.008 (error1) ± 0.05 (error2) and 〈P_c〉 = 0.325 ± 0.008 (error1) ± 0.05 (error2), where the "error1" value represents the standard error of the mean and the "error2" value is based on the error of an individual RRL period calculated from our synthetic light curve simulations. The distribution of RRab periods and the frequency of RRc stars (N_c = n_c/n_abc = 0.22) strongly suggest that these RRLs follow the general characteristics of those in Oosterhoff type I Galactic globular clusters. The metallicities of 65 individual RRab stars are calculated from the period–amplitude–metallicity relationship, yielding a mean metallicity of 〈[Fe/H]〉 = −1.48 ± 0.05 dex, where the uncertainty is the standard error of the mean. The VI minimum-light colors of the RRab stars are used to calculate a mean line-of-sight reddening toward the DISK2 field of 〈E(V − I)〉 = 0.175. By adopting this line-of-sight reddening and using a relation between RRL luminosity and metallicity (M_V = 0.23[Fe/H]+0.93), we estimate a mean distance modulus of 〈(m − M)₀〉 = 24.52 ± 0.11 for M33, where the error is the quadratic sum of the uncertainties in the absolute and dereddened V magnitudes of the RRLs. The Oosterhoff I properties of the M33 field RRL stars agree well with those of RRL populations found in the M31 halo consistent with the past interaction history of these two galaxies.

The field of exoplanetary science has diversified rapidly over recent years as the field has progressed from exoplanet detection to exoplanet characterization. For those planets known to transit, the primary transit and secondary eclipse observations have a high yield of information regarding planetary structure and atmospheres. The current restriction of these information sources to short-period planets may be abated in part through refinement of orbital parameters. This allows precision targeting of transit windows and phase variations which constrain the dynamics of the orbit and the geometric albedo of the atmosphere. Here, we describe the expected phase function variations at optical wavelengths for long-period planets, particularly those in the high-eccentricity regime and multiple systems in resonant and non-coplanar orbits. We apply this to the known exoplanets and discuss detection prospects and how observations of these signatures may be optimized by refining the orbital parameters.