Table of contents

We present long-slit spectrophotometry considering the presence of thermal inhomogeneities (t²) of two H ii regions in the Small Magellanic Cloud (SMC): NGC 456 and NGC 460. Physical conditions and chemical abundances were determined for three positions in NGC 456 and one position in NGC 460, first under the assumption of uniform temperature and then allowing for the possibility of thermal inhomogeneities. We determined t² values based on three different methods: (1) by comparing the temperature derived using oxygen forbidden lines with the temperature derived using helium recombination lines (RLs), (2) by comparing the abundances derived from oxygen forbidden lines with those derived from oxygen RLs, and (3) by comparing the abundances derived from ultraviolet carbon forbidden lines with those derived from optical carbon RLs. The first two methods averaged t² = 0.067 ± 0.013 for NGC 456 and t² = 0.036 ± 0.027 for NGC 460. These values of t² imply that when gaseous abundances are determined with collisionally excited lines they are underestimated by a factor of nearly two. From these objects and others in the literature, we find that in order to account for thermal inhomogeneities and dust depletion, the O/H ratio in low-metallicity H ii regions should be corrected by 0.25–0.45 dex depending on the thermal structure of the nebula or by 0.35 dex if such information is not available.

The Fermi Large Area Telescope has recently discovered two giant gamma-ray bubbles that extend north and south of the Galactic center with diameters and heights of the order of H ∼ 10 kpc. We suggest that the periodic star capture processes by the Galactic supermassive black hole Sgr A*, with a capture rate of τ⁻¹_cap ∼ 3 × 10⁻⁵ yr⁻¹ and an energy release of W ∼ 3 × 10⁵² erg per capture, can result in hot plasma injecting into the Galactic halo at a wind velocity of u ∼ 10⁸ cm s⁻¹. The periodic injection of hot plasma can produce a series of shocks. Energetic protons in the bubble are re-accelerated when they interact with these shocks. We show that for energy larger than E > 10¹⁵ eV, the acceleration process can be better described by the stochastic second-order Fermi acceleration. We propose that hadronic cosmic rays (CRs) within the "knee" of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Re-acceleration of these particles in the Fermi Bubble produces CRs beyond the knee. With a mean CR diffusion coefficient in this energy range in the bubble D_B ∼ 3 × 10³⁰ cm² s⁻¹, we can reproduce the spectral index of the spectrum beyond the knee and within it. The conversion efficiency from shock energy of the bubble into CR energy is about 10%. This model provides a natural explanation of the observed CR flux, spectral indices, and matching of spectra at the knee.

Young massive clusters (YMCs) with stellar masses of 10⁴–10⁵ M_☉ and core stellar densities of 10⁴–10⁵ stars per cubic pc are thought to be the "missing link" between open clusters and extreme extragalactic super star clusters and globular clusters. As such, studying the initial conditions of YMCs offers an opportunity to test cluster formation models across the full cluster mass range. G0.253 + 0.016 is an excellent candidate YMC progenitor. We make use of existing multi-wavelength data including recently available far-IR continuum (Herschel/Herschel Infrared Galactic Plane Survey) and mm spectral line (H₂O Southern Galactic Plane Survey and Millimetre Astronomy Legacy Team 90 GHz Survey) data and present new, deep, multiple-filter, near-IR (Very Large Telescope/NACO) observations to study G0.253 + 0.016. These data show that G0.253 + 0.016 is a high-mass (1.3 × 10⁵ M_☉), low-temperature (T_dust ∼ 20 K), high-volume, and column density (n ∼ 8 × 10⁴ cm⁻³; $N_{{\rm H_2}} \sim 4\times 10^{23}$ cm⁻²) molecular clump which is close to virial equilibrium (M_dust ∼ M_virial) so is likely to be gravitationally bound. It is almost devoid of star formation and, thus, has exactly the properties expected for the initial conditions of a clump that may form an Arches-like massive cluster. We compare the properties of G0.253 + 0.016 to typical Galactic cluster-forming molecular clumps and find it is extreme, and possibly unique in the Galaxy. This uniqueness makes detailed studies of G0.253 + 0.016 extremely important for testing massive cluster formation models.

To measure the magnetic field strength in the solar corona, we examined 10 fast (⩾1000 km s⁻¹) limb coronal mass ejections(CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston–shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfvén speed, and magnetic field strength in the height range 3–15 solar radii (R_s). The main results from this study are as follows: (1) the standoff distance observed in the solar corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49–3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47–1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfvén speed ranges from 259 to 982 km s⁻¹ and the magnetic field strength is in the range 6–105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of two, the Alfvén speeds and the magnetic field strengths are consistent in both methods; and (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.

Three-minute oscillations over a sunspot's umbra in AR 11131 were observed simultaneously in UV/EUV emission by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and in radio emission by the Nobeyama Radioheliograph (NoRH). We use 24 hr series of SDO and 8 hr series of NoRH observations to study spectral, spatial, and temporal variations of pulsations in the 5–9 mHz frequency range at different layers of the solar atmosphere. High spatial and temporal resolution of SDO/AIA in combination with long-duration observations allowed us to trace the variations of the cutoff frequency and spectrum of oscillations across the umbra. We found that higher frequency oscillations are more pronounced closer to the umbra's center, while the lower frequencies concentrate on the peripheral parts. We interpreted this discovery as a manifestation of variation of the magnetic field inclination across the umbra at the level of temperature minimum. Possible implications of this interpretation for the diagnostics of sunspot atmospheres are discussed.

The launch of the Hinode satellite led to the discovery of rising plumes, dark in chromospheric lines, that propagate from large (∼10 Mm) bubbles that form at the base of quiescent prominences. The plumes move through a height of approximately 10 Mm while developing highly turbulent profiles. The magnetic Rayleigh–Taylor instability was hypothesized to be the mechanism that drives these flows. In this study, using three-dimensional (3D) MHD simulations, we investigate the nonlinear stability of the Kippenhahn–Schlüter prominence model for the interchange mode of the magnetic Rayleigh–Taylor instability. The model simulates the rise of a buoyant tube inside the quiescent prominence model, where the interchange of magnetic field lines becomes possible at the boundary between the buoyant tube and the prominence. Hillier et al. presented the initial results of this study, where upflows of constant velocity (maximum found 6 km s⁻¹) and a maximum plume width ≈1.5 Mm which propagate through a height of approximately 6 Mm were found. Nonlinear interaction between plumes was found to be important for determining the plume dynamics. In this paper, using the results of ideal MHD simulations, we determine how the initial parameters for the model and buoyant tube affect the evolution of instability. We find that the 3D mode of the magnetic Rayleigh–Taylor instability grows, creating upflows aligned with the magnetic field of constant velocity (maximum found 7.3 km s⁻¹). The width of the upflows is dependent on the initial conditions, with a range of 0.5–4 Mm which propagate through heights of 3–6 Mm. These results are in general agreement with the observations of the rising plumes.

We present generalized supernova (SN) light curve (LC) models for a variety of power inputs including the previously proposed ideas of radioactive decay of ⁵⁶Ni and ⁵⁶Co and magnetar spin-down. We extend those solutions to include finite progenitor radius and stationary photospheres as might be the case for SN that are powered by interaction of the ejecta with circumstellar matter (CSM). We provide an expression for the power input that is produced by self-similar forward and reverse shocks that efficiently convert their kinetic energy into radiation. We find that this ejecta–CSM interaction luminosity that we derive is in agreement with results from multi-dimensional radiation hydrodynamics simulations in the case of an optically thin CSM. We develop a semi-analytical model for the case of an optically thick CSM by invoking an approximation for the effects of radiative diffusion similar to that adopted by Arnett for SN II and compare this model to the results of numerical radiation hydrodynamics models. This model can give complex LCs, but for monotonically declining shock input, the LCs have a smooth rise, peak, and decline. In the context of this model, we provide predictions of the shock breakout of the forward shock from the optically thick part of the CSM envelope. We also introduce a hybrid LC model that incorporates ejecta–CSM interaction plus ⁵⁶Ni and ⁵⁶Co radioactive decay input. We fit this hybrid model to the LC of the super-luminous supernova (SLSN) 2006gy. We find that shock heating produced by ejecta–CSM interaction plus some contribution from radioactive decay provides a better fit to the LC of this event than previously presented models. We also address the relation between SN IIL and SN IIn with ejecta–CSM interaction models. The faster decline of SN IIL can be reproduced by the diffusion of previously deposited shock power if the shock power input to the diffusive component vanishes when the reverse shock sweeps up the whole ejecta and/or the forward shock propagates through the optically thick CSM. A CSM interaction with forward and reverse shock power input can produce the LCs of SN IIn in terms of duration, shape, and decline rate, depending on the properties of the CSM envelope and the progenitor star. This model can also produce LCs that are symmetric in shape around peak luminosity, which is the case for the observed LCs of some recently discovered peculiar transient events. We conclude that the observed LC variety of SN IIn and of some SLSNe is likely to be a byproduct of the large range of conditions relevant to significant ejecta–CSM interaction as a power source.

We report on the development of Mezcal-SRHD, a new adaptive mesh refinement, special relativistic hydrodynamics (SRHD) code, developed with the aim of studying the highly relativistic flows in gamma-ray burst sources. The SRHD equations are solved using finite-volume conservative solvers, with second-order interpolation in space and time. The correct implementation of the algorithms is verified by one-dimensional (1D) and multi-dimensional tests. The code is then applied to study the propagation of 1D spherical impulsive blast waves expanding in a stratified medium with ρ∝r^−k, bridging between the relativistic and Newtonian phases (which are described by the Blandford–McKee and Sedov–Taylor self-similar solutions, respectively), as well as to a two-dimensional (2D) cylindrically symmetric impulsive jet propagating in a constant density medium. It is shown that the deceleration to nonrelativistic speeds in one dimension occurs on scales significantly larger than the Sedov length. This transition is further delayed with respect to the Sedov length as the degree of stratification of the ambient medium is increased. This result, together with the scaling of position, Lorentz factor, and the shock velocity as a function of time and shock radius, is explained here using a simple analytical model based on energy conservation. The method used for calculating the afterglow radiation by post-processing the results of the simulations is described in detail. The light curves computed using the results of 1D numerical simulations during the relativistic stage correctly reproduce those calculated assuming the self-similar Blandford–McKee solution for the evolution of the flow. The jet dynamics from our 2D simulations and the resulting afterglow light curves, including the jet break, are in good agreement with those presented in previous works. Finally, we show how the details of the dynamics critically depend on properly resolving the structure of the relativistic flow.

We present Kepler observations of the bright (V = 8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequency–power spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34 ± 0.06 M_☉ and 1.86 ± 0.04 R_☉, respectively, as well as yielding an age of 2.84 ± 0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3σ) that the transit event is caused by a 1.64 ± 0.04 R_Earth exoplanet in a 2.785755 ± 0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ∼10 M_Earth (2σ). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.

We present a star formation rate (SFR) calibration based on optical data that is consistent with average observed rates in both the red and blue galaxy populations at z ∼ 1. The motivation for this study is to calculate SFRs for DEEP2 Redshift Survey galaxies in the 0.7 < z < 1.4 redshift range, but our results are generally applicable to similar optically selected galaxy samples without requiring UV or IR data. Using SFR fits from UV/optical spectral energy distributions (SEDs) in the All-Wavelength Extended Groth Strip International Survey, we explore the behavior of rest-frame B-band magnitude, observed [O ii] luminosity, and rest-frame color with SED-fit SFR for both red sequence and blue cloud galaxies. The resulting SFR calibration is based on three optical-band observables: M_B, (U − B), and (B − V). The best-fit linear relation produces residual errors of 0.3 dex rms scatter for the full color-independent sample with minimal correlated residual error in L[O ii] or stellar mass. We then compare the calibrated z ∼ 1 SFRs to two diagnostics that use L[O ii] as a tracer in local galaxies and correct for dust extinction at intermediate redshifts through either galaxy B-band luminosity or stellar mass. We find that an L[O ii]–M_B SFR calibration commonly used in the literature agrees well with our calculated SFRs after correcting for the average B-band luminosity evolution in L_* galaxies. However, we find better agreement with a local L[O ii]-based SFR calibration that includes stellar mass to correct for reddening effects, indicating that stellar mass is a better tracer of dust extinction for all galaxy types and less affected by systematic evolution than galaxy luminosity from z = 1 to the current epoch.

We present improved synthesis models of the evolving spectrum of the UV/X-ray diffuse background, updating and extending our previous results. Five new main components are added to our radiative transfer code CUBA: (1) the sawtooth modulation of the background intensity from resonant line absorption in the Lyman series of cosmic hydrogen and helium; (2) the X-ray emission from the obscured and unobscured quasars that gives origin to the X-ray background; (3) a piecewise parameterization of the distribution in redshift and column density of intergalactic absorbers that fits recent measurements of the mean free path of 1 ryd photons; (4) an accurate treatment of the photoionization structure of absorbers, which enters in the calculation of the helium continuum opacity and recombination emissivity; and (5) the UV emission from star-forming galaxies at all redshifts. We provide tables of the predicted H i and He ii photoionization and photoheating rates for use, e.g., in cosmological hydrodynamics simulations of the Lyα forest and a new metallicity-dependent calibration to the UV luminosity density-star formation rate density relation. A "minimal cosmic reionization model" is also presented in which the galaxy UV emissivity traces recent determinations of the cosmic history of star formation, the luminosity-weighted escape fraction of hydrogen-ionizing radiation increases rapidly with look-back time, the clumping factor of the high-redshift intergalactic medium evolves following the results of hydrodynamic simulations, and Population III stars and miniquasars make a negligible contribution to the metagalactic flux. The model provides a good fit to the hydrogen-ionization rates inferred from flux decrement and proximity effect measurements, predicts that cosmological H ii (He iii) regions overlap at redshift 6.7 (2.8), and yields an optical depth to Thomson scattering, τ_es = 0.084 that is in agreement with Wilkinson Microwave Anisotropy Probe results. Our new background intensities and spectra are sensitive to a number of poorly determined input parameters and suffer from various degeneracies. Their predictive power should be constantly tested against new observations. We are therefore making our redshift-dependent UV/X emissivities and CUBA outputs freely available for public use at http://www.ucolick.org/~pmadau/CUBA.

We present the first N-band nulling plus K- and L-band V ² observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2–12 μm wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative "sub-micron" (0.1 μm) and "micron" (2 μm) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast to the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of eight binary-lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a 3σ confidence level for three events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretical prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is q ∼ 0.1, making the companion of the lens a strong brown dwarf candidate.

The Pan-STARRS1 survey is obtaining multi-epoch imaging in five bands (g_P1r_P1i_P1z_P1y_P1) over the entire sky north of declination −30 deg. We describe here the implementation of the Photometric Classification Server (PCS) for Pan-STARRS1. PCS will allow the automatic classification of objects into star/galaxy/quasar classes based on colors and the measurement of photometric redshifts for extragalactic objects, and will constrain stellar parameters for stellar objects, working at the catalog level. We present tests of the system based on high signal-to-noise photometry derived from the Medium-Deep Fields of Pan-STARRS1, using available spectroscopic surveys as training and/or verification sets. We show that the Pan-STARRS1 photometry delivers classifications and photometric redshifts as good as the Sloan Digital Sky Survey (SDSS) photometry to the same magnitude limits. In particular, our preliminary results, based on this relatively limited data set down to the SDSS spectroscopic limits, and therefore potentially improvable, show that stars are correctly classified as such in 85% of cases, galaxies in 97%, and QSOs in 84%. False positives are less than 1% for galaxies, ≈19% for stars, and ≈28% for QSOs. Moreover, photometric redshifts for 1000 luminous red galaxies up to redshift 0.5 are determined to 2.4% precision (defined as 1.48 × Median|z_phot − z_spec|/(1 + z)) with just 0.4% catastrophic outliers and small (−0.5%) residual bias. For bluer galaxies up to the same redshift, the residual bias (on average −0.5%) trend, percentage of catastrophic failures (1.2%), and precision (4.2%) are higher, but still interestingly small for many science applications. Good photometric redshifts (to 5%) can be obtained for at most 60% of the QSOs of the sample. PCS will create a value-added catalog with classifications and photometric redshifts for eventually many millions of sources.

We present CO(3–2) interferometric observations of the central region of the Seyfert 2 galaxy NGC 1068 using the Submillimeter Array, together with CO(1–0) data taken with the Owens Valley Radio Observatory Millimeter Array. Both the CO(3–2) and CO(1–0) emission lines are mainly distributed within ∼5 arcsec of the nucleus and along the spiral arms, but the intensity distributions show differences: the CO(3–2) map peaks in the nucleus, while the CO(1–0) emission is mainly located along the spiral arms. The CO(3–2)/CO(1–0) ratio is about 3.1 in the nucleus, which is four times as large as the average line ratio in the spiral arms, suggesting that the molecular gas there must be affected by the radiation arising from the active galactic nucleus. On the other hand, the line ratios in the spiral arms vary over a wide range from 0.24 to 2.34 with an average value around 0.75, which is similar to the line ratios of star formation regions, indicating that the molecular gas is affected by star formation. Besides, we see a tight correlation between CO(3–2)/(1–0) ratios in the spiral arms and star formation rate surface densities derived from Spitzer 8 μm dust flux densities. We also compare the CO(3–2)/(1–0) ratio and the star formation rate at different positions within the spiral arms; both are found to decrease as the radius from the nucleus increases.

We present a survey of the X-ray-emitting ejecta in the Cassiopeia A supernova remnant (SNR) based on an extensive analysis of over 6000 spectral regions extracted on 25–10'' angular scales using the Chandra 1 Ms observation. We interpret these results in the context of hydrodynamical models for the evolution of the remnant. The distributions of fitted temperature and ionization age, and the implied mass coordinates, are highly peaked and suggest that the ejecta were subjected to multiple secondary shocks following reverse shock interaction with ejecta inhomogeneities. Based on the fitted emission measure and element abundances, and an estimate of the emitting volume, we derive masses for the X-ray-emitting ejecta and also show the distribution of the mass of various elements over the remnant. An upper limit to the total shocked Fe mass visible in X-rays appears to be roughly 0.13 M_☉, which accounts for nearly all of the mass expected in Fe ejecta. We find two populations of Fe ejecta, that associated with normal Si burning and that possibly associated with α-rich freezeout, with a mass ratio of approximately 2:1. Essentially all of the observed Fe (both components) lies well outside the central regions of the SNR, possibly having been ejected by hydrodynamic instabilities during the explosion. We discuss this and its implications for the neutron star kick.

High-frequency quasi-periodic oscillations (QPOs) from weakly magnetized neutron stars display rapid frequency variability (second timescales) and high coherence with quality factors up to at least 200 at frequencies about 800–850 Hz. Their parameters have been estimated so far from standard min(χ²) fitting techniques, after combining a large number of power density spectra (PDS), to have the powers normally distributed (the so-called Gaussian regime). Before combining PDS, different methods to minimize the effects of the frequency drift to the estimates of the QPO parameters have been proposed, but none of them relied on fitting the individual PDS. Accounting for the statistical properties of PDS, we apply a maximum likelihood method to derive the QPO parameters in the non-Gaussian regime. The method presented is general, easy to implement, and can be applied to fitting individual PDS, several PDS simultaneously, or their average, and is obviously not specific to the analysis of kHz QPO data. It applies to the analysis of any PDS optimized in frequency resolution and for low-frequency variability or PDS containing features whose parameters vary on short timescales, as is the case for kHz QPOs. It is equivalent to the standard χ² minimization fitting when the number of PDS fitted is large. The accuracy, reliability, and superiority of the method is demonstrated with simulations of synthetic PDS, containing Lorentzian QPOs of known parameters. Accounting for the broadening of the QPO profile, due to the leakage of power inherent to windowed Fourier transforms, the maximum likelihood estimates of the QPO parameters are asymptotically unbiased and have negligible bias when the QPO is reasonably well detected. By contrast, we show that the standard min(χ²) fitting method gives biased parameters with larger uncertainties. The maximum likelihood fitting method is applied to a subset of archival Rossi X-ray Timing Explorer data of the neutron star X-ray binary 4U1608-522, for which we show that the lower kHz QPO parameters can be measured on timescales as short as 8 s. To demonstrate the potential use of the results of the maximum likelihood method, we show that in the observation analyzed the time evolution of the frequency is consistent with a random walk. We then show that the broadening of the QPO due to the frequency drift scales as $\sqrt{T}$, as expected from a random walk (T is the integration time of the PDS). This enables us to estimate the intrinsic quality factor of the QPO to be ∼260, whereas previous analysis indicated a maximum value around 200.

Large and heterogeneous isotopic variations of ¹⁵⁰Sm/¹⁴⁹Sm and ¹⁵⁸Gd/¹⁵⁷Gd due to neutron capture reactions caused by cosmic-ray irradiation were found in chemical and mineral separates from the Norton County meteorite. The light-colored separates, consisting mainly of enstatite (Mg₂Si₂O₆), have a very large neutron fluence of 1.98 × 10¹⁷ n cm⁻², which is 10 times higher than that of the whole rock. Furthermore, four chemical separates showed a large variation in neutron fluences, ranging from 1.82 × 10¹⁶ to 1.87 × 10¹⁷ n cm⁻². The variable amounts of neutron fluences from a small single fragment of the Norton County meteorite cannot be simply explained by single-stage cosmic-ray irradiation in space. Rare earth element (REE) analyses revealed that the fractions with high neutron fluences have similar chemical properties to those in the early condensates in the solar system, showing depletions of Eu and Yb in their REE abundance patterns. The data provide evidence for an activity of the early Sun (T Tauri), suggesting the migration of early and intense irradiation materials into the Norton County meteorite's parent body.

We investigate the role discrete clumps embedded in an astrophysical jet play on the jet's morphology and line emission characteristics. By varying clumps' size, density, position, and velocity, we cover a range of parameter space motivated by observations of objects such as the Herbig–Haro object HH 34. We here extend the results presented in Yirak et al., including how analysis of individual observations may lead to spurious sinusoidal variation whose parameters vary widely over time, owing chiefly to interactions between clumps. The goodness of fits, while poor in all simulations, are best when clump–clump collisions are minimal. Our results indicate that a large velocity dispersion leads to a clump–clump collision-dominated flow which disrupts the jet beam. Finally, we present synthetic emission images of Hα and [S ii] and note an excess of [S ii] emission along the jet length as compared to observations. This suggests that observed beams undergo earlier processing, if they are present at all.

A systematic study of the synchrotron X-ray emission from supernova remnants (SNRs) has been conducted. We selected a total of 12 SNRs whose synchrotron X-ray spectral parameters are available in the literature with reasonable accuracy and studied how their luminosities change as a function of radius. It is found that the synchrotron X-ray luminosity tends to drop especially when the SNRs become larger than ∼5 pc, despite large scatter. This may be explained by the change of spectral shape caused by the decrease of the synchrotron roll-off energy. A simple evolutionary model of the X-ray luminosity is proposed and is found to reproduce the observed data approximately, with reasonable model parameters. According to the model, the total energy of accelerated electrons is estimated to be 10^47-48 erg, which is well below the supernova explosion energy. The maximum energies of accelerated electrons and protons are also discussed.

Observations of spiral galaxies show a strong linear correlation between the ratio of molecular to atomic hydrogen surface density R_mol and midplane pressure. To explain this, we simulate three-dimensional, magnetized turbulence, including simplified treatments of non-equilibrium chemistry and the propagation of dissociating radiation, to follow the formation of H₂ from cold atomic gas. The formation timescale for H₂ is sufficiently long that equilibrium is not reached within the 20–30 Myr lifetimes of molecular clouds. The equilibrium balance between radiative dissociation and H₂ formation on dust grains fails to predict the time-dependent molecular fractions we find. A simple, time-dependent model of H₂ formation can reproduce the gross behavior, although turbulent density perturbations increase molecular fractions by a factor of few above it. In contradiction to equilibrium models, radiative dissociation of molecules plays little role in our model for diffuse radiation fields with strengths less than 10 times that of the solar neighborhood, because of the effective self-shielding of H₂. The observed correlation of R_mol with pressure corresponds to a correlation with local gas density if the effective temperature in the cold neutral medium of galactic disks is roughly constant. We indeed find such a correlation of R_mol with density. If we examine the value of R_mol in our local models after a free-fall time at their average density, as expected for models of molecular cloud formation by large-scale gravitational instability, our models reproduce the observed correlation over more than an order-of-magnitude range in density.

We use high-resolution (∼01) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z ∼ 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M_V ≲ −18, M_* > 10^9.5 M_☉) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% ± 11%, 65% ± 11%, and 60% ± 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of ±11%) across environments which span two orders of magnitude in galaxy number density (n ∼ 300–10,000 galaxies Mpc⁻³) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (∼50 pc) to analyze a sample of 333 faint (M_V > −18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.

This is the second in a series of papers discussing the process and effects of star formation in the self-gravitating disk around the supermassive black holes in active galactic nuclei (AGNs). We have previously suggested that warm skins are formed above the star-forming (SF) disk through the diffusion of warm gas driven by supernova explosions. Here we study the evolution of the warm skins when they are exposed to the powerful radiation from the inner part of the accretion disk. The skins initially are heated to the Compton temperature, forming a Compton atmosphere (CAS) whose subsequent evolution is divided into four phases. Phase I is the duration of pure accumulation supplied by the SF disk. During phase II clouds begin to form due to line cooling and sink to the SF disk. Phase III is a period of preventing clouds from sinking to the SF disk through dynamic interaction between clouds and the CAS because of the CAS overdensity driven by continuous injection of warm gas from the SF disk. Finally, phase IV is an inevitable collapse of the entire CAS through line cooling. This CAS evolution drives the episodic appearance of broad-line regions (BLRs). We follow the formation of cold clouds through the thermal instability of the CAS during phases II and III, using linear analysis. Since the clouds are produced inside the CAS, the initial spatial distribution of newly formed clouds and angular momentum naturally follow the CAS dynamics, producing a flattened disk of clouds. The number of clouds in phases II and III can be estimated, as well as the filling factor of clouds in the BLR. Since the cooling function depends on the metallicity, the metallicity gradients that originate in the SF disk give rise to different properties of clouds in different radial regions. We find from the instability analysis that clouds have column density N_H ≲ 10²² cm⁻² in the metal-rich regions whereas they have N_H ≳ 10²² cm⁻² in the metal-poor regions. The metal-rich clouds compose the high-ionization line regions whereas the metal-poor clouds are in low-ionization line (LIL) regions. Since metal-rich clouds are optically thin, they will be blown away by radiation pressure, forming the observed outflows. The outflowing clouds could set up a metallicity correlation between the BLRs and narrow-line regions. The LIL regions are episodic due to the mass cycle of clouds with the CAS in response to continuous injection by the SF disk, giving rise to different types of AGNs. Based on Sloan Digital Sky Survey quasar spectra, we identify a spectral sequence in light of emission-line equivalent width from phase I to IV. A key phase in the episodic appearance of the BLRs is bright type II AGNs with no or only weak BLRs, contrary to the popular picture in which the absence of a BLR is due to a low accretion rate. We discuss observational implications and tests of the theoretical predictions of this model.

We present a statistical study of the luminosity functions of galaxies surrounding luminous red galaxies (LRGs) at average redshifts 〈z〉 = 0.34 and 〈z〉 = 0.65. The luminosity functions are derived by extracting source photometry around more than 40,000 LRGs and subtracting foreground and background contamination using randomly selected control fields. We show that at both studied redshifts the average luminosity functions of the LRGs and their satellite galaxies are poorly fitted by a Schechter function due to a luminosity gap between the centrals and their most luminous satellites. We utilize a two-component fit of a Schechter function plus a log-normal distribution to demonstrate that LRGs are typically brighter than their most luminous satellite by roughly 1.3 mag. This luminosity gap implies that interactions within LRG environments are typically restricted to minor mergers with mass ratios of 1:4 or lower. The luminosity functions further imply that roughly 35% of the mass in the environment is locked in the LRG itself, supporting the idea that mass growth through major mergers within the environment is unlikely. Lastly, we show that the luminosity gap may be at least partially explained by the selection of LRGs as the gap can be reproduced by sparsely sampling a Schechter function. In that case LRGs may represent only a small fraction of central galaxies in similar mass halos.

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the intensity of structures. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model (β-model or Sérsic profile) with elliptical symmetry, from the X-ray image. Our method is applied to 34 clusters observed by the Chandra Space Telescope that are in the redshift range z ∈ [0.02, 0.2] and have a signal-to-noise ratio (S/N) greater than 100. We present the calibration of the method and the relations between the substructure level with physical quantities, such as the mass, X-ray luminosity, temperature, and cluster redshift. We use our method to separate the clusters in two sub-samples of high- and low-substructure levels. We conclude, using Monte Carlo simulations, that the method recuperates very well the true amount of substructure for small angular core radii clusters (with respect to the whole image size) and good S/N observations. We find no evidence of correlation between the substructure level and physical properties of the clusters such as gas temperature, X-ray luminosity, and redshift; however, analysis suggest a trend between the substructure level and cluster mass. The scaling relations for the two sub-samples (high- and low-substructure level clusters) are different (they present an offset, i.e., given a fixed mass or temperature, low-substructure clusters tend to be more X-ray luminous), which is an important result for cosmological tests using the mass–luminosity relation to obtain the cluster mass function, since they rely on the assumption that clusters do not present different scaling relations according to their dynamical state.

Following the discovery of a new radio component right before the GeV γ-ray detection since 2008 August by the Fermi Gamma-ray Space Telescope, we present a detailed study of the kinematics and light curve on the central sub-parsec scale of 3C 84 using the archival Very Long Baseline Array 43 GHz data covering the period between 2002 January and 2008 November. We find that the new component "C3," previously reported by the observations with the Very Long Baseline Interferometer Exploration of Radio Astrometry, was already formed in 2003. The flux density of C3 increases moderately until 2008, and then it becomes brighter rapidly after 2008. The radio core, C1, also shows a similar trend. The apparent speed of C3 with reference to the core C1 shows moderate acceleration from 0.10c to 0.47c between 2003 November and 2008 November, but is still sub-relativistic. We further try to fit the observed broadband spectrum by the one-zone synchrotron self-Compton model using the measured apparent speed of C3. The fit can reproduce the observed γ-ray emission, but does not agree with the observed radio spectral index between 22 and 43 GHz.

VERITAS has been monitoring the very-high-energy (VHE; > 100 GeV) gamma-ray activity of the radio galaxy M 87 since 2007. During 2008, flaring activity on a timescale of a few days was observed with a peak flux of (0.70  ±  0.16) × 10⁻¹¹ cm⁻² s⁻¹ at energies above 350 GeV. In 2010 April, VERITAS detected a flare from M 87 with peak flux of (2.71  ±  0.68) × 10⁻¹¹ cm⁻² s⁻¹ for E > 350 GeV. The source was observed for six consecutive nights during the flare, resulting in a total of 21 hr of good-quality data. The most rapid flux variation occurred on the trailing edge of the flare with an exponential flux decay time of 0.90^+0.22_−0.15 days. The shortest detected exponential rise time is three times as long, at 2.87^+1.65_−0.99 days. The quality of the data sample is such that spectral analysis can be performed for three periods: rising flux, peak flux, and falling flux. The spectra obtained are consistent with power-law forms. The spectral index at the peak of the flare is equal to 2.19  ±  0.07. There is some indication that the spectrum is softer in the falling phase of the flare than the peak phase, with a confidence level corresponding to 3.6 standard deviations. We discuss the implications of these results for the acceleration and cooling rates of VHE electrons in M 87 and the constraints they provide on the physical size of the emitting region.

High-resolution data of the peculiar magnetic massive star HD 148937 were obtained with Chandra-HETGS, and are presented here in combination with a re-analysis of the older XMM-RGS data. The lines of the high-Z elements (Mg, Si, S) were found to be unshifted and relatively narrow (FWHM of about 800 km s⁻¹), i.e., narrower than the O line recorded by RGS, which possibly indicates that the hot plasma is multi-thermal and has several origins. These data further indicate a main plasma temperature of about 0.6 keV and a formation of the X-ray emission at about one stellar radius above the photosphere. From the spectral fits and the H-to-He line ratios, the presence of very hot plasma is, however, confirmed, though with a smaller relative strength than for the prototype magnetic oblique rotator θ¹ Ori C. Both stars thus share many similarities, but HD 148937 appears less extreme than θ¹ Ori C despite also having a large magnetic confinement parameter.

In order to estimate the mass and age of stars, we construct a grid of stellar models for eight solar-analog stars including diffusion and rotation-induced mixing for the given ranges of stellar mass, metallicity, and rotational rate. By combining stellar models with observational data including lithium abundance, we obtain more accurate estimations of mass and age for solar-analog stars. The results indicate that stars HIP 56948, HIP 73815, and HIP 78399 are three possible solar twins. Furthermore, we find that lithium depletion due to extra-mixing in solar analogs strongly depends on mass, metallicity, and rotational history. Therefore, lithium abundance can be used as a good constraint in stellar modeling.

We present the initial–final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting theoretical model atmospheres to the observed spectrum using a χ² fitting algorithm. The cooling time and mass were obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main-sequence component to an uncertainty of about 0.17 dex in log t. The difference between the total age and white dwarf cooling time is taken as the main-sequence lifetime of each white dwarf. The initial mass of each white dwarf was then determined using stellar evolution tracks with a corresponding metallicity derived from spectra of their main-sequence companions, thus yielding the initial–final mass relation. Most of the initial masses of the white dwarf components are between 1 and 2 M_☉. Our results suggest a correlation between the metallicity of a white dwarf's progenitor and the amount of post-main-sequence mass loss it experiences—at least among progenitors with masses in the range of 1–2 M_☉. A comparison of our observations to theoretical models suggests that low-mass stars preferentially lose mass on the red giant branch.

We study the evolution of stellar mass in galaxies as a function of host halo mass, using the "MPA" and "Durham" semi-analytic models, implemented on the Millennium Run simulation. For both models, the stellar mass of the central galaxies increases rapidly with halo mass at the low-mass end and more slowly in halos of larger masses at the three redshifts probed (z ∼ 0, 1, 2). About 45% of the stellar mass in central galaxies in present-day halos less massive than ∼10¹² h⁻¹ M_☉ is already in place at z ∼ 1, and this fraction increases to ∼65% for more massive halos. The baryon conversion efficiency into stars has a peaked distribution with halo mass, and the peak location shifts toward lower mass from z ∼ 1 to z ∼ 0. The stellar mass in low-mass halos grows mostly by star formation since z ∼ 1, while in high-mass halos most of the stellar mass is assembled by mergers, reminiscent of "downsizing." We compare our findings to empirical results from the Sloan Digital Sky Survey and DEEP2 surveys utilizing galaxy clustering measurements to study galaxy evolution. The theoretical predictions are in qualitative agreement with these phenomenological results, but there are large discrepancies. The most significant one concerns the number of stars already in place in the progenitor galaxies at z ∼ 1, which is about a factor of two larger in both semi-analytic models. We demonstrate that methods studying galaxy evolution from the galaxy–halo connection are powerful in constraining theoretical models and can guide future efforts of modeling galaxy evolution. Conversely, semi-analytic models serve an important role in improving such methods.

Coronal cavities are voids in coronal emission often observed above high latitude filament channels. Sometimes, these cavities have areas of bright X-ray emission in their centers. In this study, we use data from the X-ray Telescope (XRT) on the Hinode satellite to examine the thermal emission properties of a cavity observed during 2008 July that contains bright X-ray emission in its center. Using ratios of XRT filters, we find evidence for elevated temperatures in the cavity center. The area of elevated temperature evolves from a ring-shaped structure at the beginning of the observation, to an elongated structure two days later, finally appearing as a compact round source four days after the initial observation. We use a morphological model to fit the cavity emission, and find that a uniform structure running through the cavity does not fit the observations well. Instead, the observations are reproduced by modeling several short cylindrical cavity "cores" with different parameters on different days. These changing core parameters may be due to some observed activity heating different parts of the cavity core at different times. We find that core temperatures of 1.75 MK, 1.7 MK, and 2.0 MK (for July 19, July 21, and July 23, respectively) in the model lead to structures that are consistent with the data, and that line-of-sight effects serve to lower the effective temperature derived from the filter ratio.

We present, for the first time, measurements of arc-polarized velocity variations together with magnetic field variations associated with a large-amplitude Alfvén wave as observed by the Wind satellite. The module of the magnetic field variance is larger than the magnitude of the average magnetic field, indicating the large amplitude of these fluctuations. When converting to the deHoffman–Teller frame, we find that the magnetic field and velocity vector components, in the plane perpendicular to the minimum-variance direction of the magnetic field, are arc-polarized, and their tips almost lie on the same circle. We also find that the normalized cross helicity and Alfvén ratio of the wave are both nearly equal to unity, a result which has not been reported in previous studies at 1 AU. It is worthy to stress here that pure Alfvén waves can also exist in the solar wind even near the Earth at 1 AU, but not only near 0.3 AU. Further study could be done to help us know more about the properties of pure Alfvén wave at 1 AU that could not be figured out easily before because of the contaminations (e.g., Alfvén waves propagating in different directions, magnetic structures, and other compressional waves) on previously reported Alfvén wave cases.

The gamma-ray space telescopes AGILE and Fermi detected short and bright synchrotron gamma-ray flares at photon energies above 100 MeV in the Crab Nebula. This discovery suggests that electron–positron pairs in the nebula are accelerated to PeV energies in a milligauss magnetic field, which is difficult to explain with classical models of particle acceleration and pulsar wind nebulae. We investigate whether particle acceleration in a magnetic reconnection layer can account for the puzzling properties of the flares. We numerically integrate relativistic test-particle orbits in the vicinity of the layer, including the radiation reaction force, and using analytical expressions for the large-scale electromagnetic fields. As they get accelerated by the reconnection electric field, the particles are focused deep inside the current layer where the magnetic field is small. The electrons suffer less from synchrotron losses and are accelerated to extremely high energies. Population studies show that, at the end of the layer, the particle distribution piles up at the maximum energy given by the electric potential drop and is focused into a thin fan beam. Applying this model to the Crab Nebula, we find that the emerging synchrotron emission spectrum peaks above 100 MeV and is close to the spectral shape of a single electron. The flare inverse Compton emission is negligible and no detectable emission is expected at other wavelengths. This mechanism provides a plausible explanation for the gamma-ray flares in the Crab Nebula and could be at work in other astrophysical objects such as relativistic jets in active galactic nuclei.

The observed radial and vertical metallicity distribution of old stars in the Milky Way disk provides a powerful constraint on the chemical enrichment and dynamical history of the disk system. We present the radial metallicity gradient, Δ[Fe/H]/ΔR, as a function of height above the plane, |Z|, using 7010 main-sequence turnoff stars observed by the Sloan Extension for Galactic Understanding and Exploration survey. The sample consists of mostly old thin and thick disk stars, with a minimal contribution from the stellar halo, in the region 6 kpc < R < 16 kpc, 0.15 kpc < |Z| < 1.5 kpc. The data reveal that the radial metallicity gradient becomes flat at heights |Z| > 1 kpc. The median metallicity at large |Z| is consistent with the metallicities seen in outer disk open clusters, which exhibit a flat radial gradient at [Fe/H] ∼−0.5. We note that the outer disk clusters are also located at large |Z|; because the flat gradient extends to small R for our sample, there is some ambiguity in whether the observed trends for clusters are due to a change in R or |Z|. We therefore stress the importance of considering both the radial and vertical directions when measuring spatial abundance trends in the disk. The flattening of the gradient at high |Z| also has implications on thick disk formation scenarios, which predict different metallicity patterns in the thick disk. A flat gradient, such as we observe, is predicted by a turbulent disk at high redshift, but may also be consistent with radial migration, as long as mixing is strong. We test our analysis methods using a mock catalog based on the model of Schönrich & Binney, and we estimate our distance errors to be ∼25%. We also show that we can properly correct for selection biases by assigning weights to our targets.

While the seismic quality factor and phase lag are defined solely by the bulk properties of the mantle, their tidal counterparts are determined by both the bulk properties and the size effect (self-gravitation of a body as a whole). For a qualitative estimate, we model the body with a homogeneous sphere, and express the tidal phase lag through the lag in a sample of material. Although simplistic, our model is sufficient to understand that the lags are not identical. The difference emerges because self-gravitation pulls the tidal bulge down. At low frequencies, this reduces strain and the damping rate, making tidal damping less efficient in larger objects. At higher frequencies, competition between self-gravitation and rheology becomes more complex, though for sufficiently large super-Earths the same rule applies: the larger the planet, the weaker the tidal dissipation in it. Being negligible for small terrestrial planets and moons, the difference between the seismic and tidal lagging (and likewise between the seismic and tidal damping) becomes very considerable for large exoplanets (super-Earths). In those, it is much lower than what one might expect from using a seismic quality factor. The tidal damping rate deviates from the seismic damping rate, especially in the zero-frequency limit, and this difference takes place for bodies of any size. So the equal in magnitude but opposite in sign tidal torques, exerted on one another by the primary and the secondary, have their orbital averages going smoothly through zero as the secondary crosses the synchronous orbit. We describe the mantle rheology with the Andrade model, allowing it to lean toward the Maxwell model at the lowest frequencies. To implement this additional flexibility, we reformulate the Andrade model by endowing it with a free parameter ζ which is the ratio of the anelastic timescale to the viscoelastic Maxwell time of the mantle. Some uncertainty in this parameter's frequency dependence does not influence our principal conclusions.

The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 − 6) × 10⁹ M_☉) provides a unique opportunity to investigate the origin of very high energy (VHE; E  > 100 GeV) γ-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE γ-ray emitter since 2006. The VHE γ-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE γ-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of τ^rise_d = (1.69 ± 0.30) days and τ^decay_d = (0.611 ± 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (∼day), peak fluxes (Φ_>0.35 TeV ≃ (1–3) × 10⁻¹¹ photons cm⁻² s⁻¹), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken ∼3 days after the peak of the VHE γ-ray emission reveal an enhanced flux from the core (flux increased by factor ∼2; variability timescale <2 days). The long-term (2001–2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE γ-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002–2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE γ-ray emission from M 87 are reviewed in the light of the new data.

We present a study of the solar coronal shock wave on 2005 November 14 associated with the GOES M3.9 flare that occurred close to the east limb (S06° E60°). The shock signature, a type II radio burst, had an unusually high starting frequency of about 800 MHz, indicating that the shock was formed at a rather low height. The position of the radio source, the direction of the shock wave propagation, and the coronal electron density were estimated using Nançay Radioheliograph observations and the dynamic spectrum of the Green Bank Solar Radio Burst Spectrometer. The soft X-ray, Hα, and Reuven Ramaty High Energy Solar Spectroscopic Imager observations show that the flare was compact, very impulsive, and of a rather high density and temperature, indicating a strong and impulsive increase of pressure in a small flare loop. The close association of the shock wave initiation with the impulsive energy release suggests that the impulsive increase of the pressure in the flare was the source of the shock wave. This is supported by the fact that, contrary to the majority of events studied previously, no coronal mass ejection was detected in association with the shock wave, although the corresponding flare occurred close to the limb.

We have obtained deep, high spatial and spectral resolution, long-slit spectra of the Hα nebulae in the cool cores of nine galaxy clusters. This sample provides a wealth of information on the ionization state, kinematics, and reddening of the warm gas in the cool cores of galaxy clusters. We find evidence for only small amounts of reddening in the extended, line-emitting filaments, with the majority of filaments having E(B − V) < 0.2. We find, in agreement with previous works, that the optical emission in cool core clusters has elevated low-ionization line ratios. The combination of [O iii]/Hβ, [N ii]/Hα, [S ii]/Hα, and [O i]/Hα allow us to rule out collisional ionization by cosmic rays, thermal conduction, and photoionization by intracluster medium (ICM) X-rays and active galactic nuclei as strong contributors to the ionization in the bulk of the optical line-emitting gas in both the nuclei and filaments. The data are adequately described by a composite model of slow shocks and star formation. This model is further supported by an observed correlation between the line widths and low-ionization line ratios which becomes stronger in systems with more modest star formation activity based on far-ultraviolet observations. We find that the more extended, narrow filaments tend to have shallower velocity gradients and narrower line widths than the compact filamentary complexes. We confirm that the widths of the emission lines decrease with radius, from FWHM ∼600 km s⁻¹ in the nuclei to FWHM ∼100 km s⁻¹ in the most extended filaments. The variation of line width with radius is vastly different than what is measured from stellar absorption lines in a typical giant elliptical galaxy, suggesting that the velocity width of the warm gas may in fact be linked to ICM turbulence and, thus, may provide a glimpse into the amount of turbulence in cool cores. In the central regions (r < 10 kpc) of several systems the warm gas shows kinematic signatures consistent with rotation, consistent with earlier work. We find that the kinematics of the most extended filaments in this sample are broadly consistent with both infall and outflow, and recommend further studies linking the warm gas kinematics to both radio and X-ray maps in order to further understand the observed kinematics.

We present an analysis of the ages and star formation history of the F-type stars in the Upper Scorpius (US), Upper Centaurus–Lupus (UCL), and Lower Centaurus–Crux (LCC) subgroups of Scorpius–Centaurus (Sco-Cen), the nearest OB association. Our parent sample is the kinematically selected Hipparcos sample of de Zeeuw et al., restricted to the 138 F-type members. We have obtained classification-resolution optical spectra and have also determined the spectroscopic accretion disk fraction. With Hipparcos and 2MASS photometry, we estimate the reddening and extinction for each star and place the candidate members on a theoretical H-R diagram. For each subgroup we construct empirical isochrones and compare to published evolutionary tracks. We find that (1) our empirical isochrones are consistent with the previously published age-rank of the Sco-Cen subgroups; (2) subgroups LCC and UCL appear to reach the main-sequence turn-on at spectral types ∼F4 and ∼F2, respectively. An analysis of the A-type stars shows US reaching the main sequence at about spectral type ∼A3. (3) The median ages for the pre-main-sequence members of UCL and LCC are 16 Myr and 17 Myr, respectively, in agreement with previous studies, however we find that (4) Upper Sco is much older than previously thought. The luminosities of the F-type stars in US are typically a factor of ∼2.5 less luminous than predicted for a 5 Myr old population for four sets of evolutionary tracks. We re-examine the evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco members, as well as the evolved M supergiant Antares, and estimate a revised mean age for Upper Sco of 11 ± 1 ± 2 Myr (statistical, systematic). Using radial velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data are statistically consistent with no expansion. We reevaluate the inferred masses for the known substellar companions in Upper Sco using the revised age and find that the inferred masses are typically ∼20%–70% higher than the original estimates which had assumed a much younger age; specifically, we estimate the mass of 1RXS J1609-2105b to be 14⁺²₋₃M_Jup, suggesting that it is a brown dwarf rather than a planet. Finally, we find the fraction of F-type stars exhibiting Hα emission and/or a K-band excess consistent with accretion to be 0/17 (<19%; 95% CL) in US at ∼11 Myr, while UCL has 1/41 (2⁺⁵₋₁%; 68% CL) accretors and LCC has 1/50 (2⁺⁴₋₁%; 68% CL) accretors at ∼16 Myr and ∼17 Myr, respectively.

We use deep Chandra imaging and an extensive optical spectroscopy campaign on the Keck 10 m telescopes to study the properties of X-ray point sources in two isolated X-ray-selected clusters, two superclusters, and one "supergroup" at redshifts of z ∼ 0.7–0.9. We first study X-ray point sources using the statistical measure of cumulative source counts, finding that the measured overdensities are consistent with previous results, but we recommend caution in overestimating the precision of the technique. Optical spectroscopy of objects matched to X-ray point sources confirms a total of 27 active galactic nuclei (AGNs) within 5 structures, and we find that their host galaxies tend to be located away from dense cluster cores. More than 36% of the host galaxies are located in the "green valley" on a color–magnitude diagram, which suggests they are a transitional population. Based on analysis of [O ii] and Hδ line strengths, the average spectral properties of the AGN host galaxies in all structures indicate either ongoing star formation or a starburst within ∼1 Gyr, and that the host galaxies are younger than the average galaxy in the parent population. These results indicate a clear connection between starburst and nuclear activity. We use composite spectra of the spectroscopically confirmed members in each structure (cluster, supergroup, or supercluster) to separate them based on a measure of the overall evolutionary state of their constituent galaxies. We define structures as having more evolved populations if their average galaxy has lower EW([O ii]) and EW(Hδ). The AGNs in the more evolved structures have lower rest-frame 0.5–8 keV X-ray luminosities (all below 10^43.3 erg s⁻¹) and longer times since a starburst than those in the unevolved structures, suggesting that the peak of both star formation and AGN activity has occurred at earlier times. With the wide range of evolutionary states and time frames in the structures, we use our results to analyze the evolution of X-ray AGNs and evaluate potential triggering mechanisms.

We present a catalog of radio afterglow observations of gamma-ray bursts (GRBs) over a 14 year period from 1997 to 2011. Our sample of 304 afterglows consists of 2995 flux density measurements (including upper limits) at frequencies between 0.6 GHz and 660 GHz, with the majority of data taken at 8.5 GHz frequency band (1539 measurements). We use this data set to carry out a statistical analysis of the radio-selected sample. The detection rate of radio afterglows has stayed unchanged almost at 31% before and after the launch of the Swift satellite. The canonical long-duration GRB radio light curve at 8.5 GHz peaks at three to six days in the source rest frame, with a median peak luminosity of 10³¹ erg s⁻¹ Hz⁻¹. The peak radio luminosities for short-hard bursts, X-ray flashes, and the supernova–GRB classes are an order of magnitude or more fainter than this value. There are clear relationships between the detectability of a radio afterglow and the fluence or energy of a GRB, and the X-ray or optical brightness of the afterglow. However, we find few significant correlations between these same GRB and afterglow properties and the peak radio flux density. We also produce synthetic light curves at centimeter and millimeter bands using a range of blast wave and microphysics parameters derived from multiwavelength afterglow modeling, and we use them to compare to the radio sample. Finding agreement, we extrapolate this behavior to predict the centimeter and millimeter behavior of GRBs observed by the Expanded Very Large Array and the Atacama Large Millimeter Array.

We have developed a relativistic model for pulsar radio emission and polarization by taking into account a detailed geometry of emission region, rotation, and modulation. The sparks activity on the polar cap leads to plasma columns in the emission region and modulated emission. By considering relativistic plasma bunches streaming out along the rotating dipolar field lines as a source of curvature radiation, we have deduced the polarization state of the radiation field in terms of the Stokes parameters. We have simulated a set of typical pulse profiles and analyzed the role of viewing geometry, rotation, and modulation in the pulsar polarization profiles. Our simulations explain most of the diverse behaviors of polarization generally found in pulsar radio profiles. We show that both the "antisymmetric" and "symmetric" types of circular polarization are possible within the framework of curvature radiation. We also show that the "kinky" nature in the polarization position angle traverses might be due to the rotation and modulation effects. The phase lag of the polarization position angle inflection point relative to the phase of core peak depends upon the rotationally induced asymmetry in the curvature of source trajectory and modulation.

We examine the hypothesis that plasma associated with "Type II" spicules is heated to coronal temperatures, and that the upward moving hot plasma constitutes a significant mass supply to the solar corona. One-dimensional hydrodynamical models including time-dependent ionization are brought to bear on the problem. These calculations indicate that heating of field-aligned spicule flows should produce significant differential Doppler shifts between emission lines formed in the chromosphere, transition region, and corona. At present, observational evidence for the computed 60–90 km s⁻¹ differential shifts is weak, but the data are limited by difficulties in comparing the proper motion of Type II spicules with spectral and kinematic properties of an associated transition region and coronal emission lines. Future observations with the upcoming infrared interferometer spectrometer instrument should clarify if Doppler shifts are consistent with the dynamics modeled here.

B2013+370 and B2023+336 are two blazars at low-galactic latitude that were previously proposed to be the counterparts for the EGRET unidentified sources 3EG J2016+3657 and 3EG J2027+3429. Gamma-ray emission associated with the EGRET sources has been detected by the FermiGamma-ray Space Telescope, and the two sources, 1FGL J2015.7+3708 and 1FGL J2027.6+3335, have been classified as unidentified in the 1 year catalog. This analysis of the Fermi Large Area Telescope (LAT) data collected during 31 months reveals that the 1FGL sources are spatially compatible with the blazars and are significantly variable, supporting the hypothesis of extragalactic origin for the gamma-ray emission. The gamma-ray light curves are compared with 15 GHz radio light curves from the 40 m telescope at the Owens Valley Radio Observatory. Simultaneous variability is seen in both bands for the two blazar candidates. The study is completed with the X-ray analysis of 1FGL J2015.7+3708 using Swift observations that were triggered in 2010 August by a Fermi-detected flare. The resulting spectral energy distribution shows a two-component structure typical of blazars. We also identify a second source in the field of view of 1FGL J2027.6+3335 with similar characteristics to the known LAT pulsars. This study gives solid evidence favoring blazar counterparts for these two unidentified EGRET and Fermi sources, supporting the hypothesis that a number of unidentified gamma-ray sources at low-galactic latitudes are indeed of extragalactic origin.

We present results of an analysis of the local (z ∼ 0) morphology–environment relation for 911 bright (M_B < −19) galaxies, based on matching classical RC3 morphologies with the Sloan Digital Sky Survey based group catalog of Yang et al., which includes halo mass estimates. This allows us to study how the relative fractions of spirals, lenticulars, and ellipticals depend on halo mass over a range of 10^11.7–10^14.8 h⁻¹ M_☉, from isolated single-galaxy halos to massive groups and low-mass clusters. We pay particular attention to how morphology relates to central versus satellite status (where "central" galaxies are the most massive within their halo). The fraction of galaxies which are elliptical is a strong function of stellar mass; it is also a strong function of halo mass, but only for central galaxies. We interpret this as evidence for a scenario where elliptical galaxies are always formed, probably via mergers, as central galaxies within their halos, with satellite ellipticals being previously central galaxies accreted onto a larger halo. The overall fraction of galaxies which are S0 increases strongly with halo mass, from ∼10% to ∼70%. Here, too, we find striking differences between the central and satellite populations. 20% ± 2% of central galaxies with stellar masses  M_* > 10^10.5 M_☉ are S0 regardless of halo mass, but satellite S0 galaxies are only found in massive (>10¹³ h⁻¹ M_☉) halos, where they are 69% ± 4% of the  M_* > 10^10.5 M_☉ satellite population. This suggests two channels for forming S0 galaxies: one which operates for central galaxies and another which transforms lower-mass ( M_* ≲ 10¹¹ M_☉) accreted spirals into satellite S0 galaxies in massive halos. Analysis of finer morphological structure (bars and rings in disk galaxies) shows some trends with stellar mass, but none with halo mass; this is consistent with other recent studies which indicate that bars are not strongly influenced by galaxy environment. Radio sources in high-mass central galaxies are common, similarly so for elliptical and S0 galaxies, with a frequency that increases with the halo mass. Emission-line active galactic nuclei (mostly LINERs) are more common in S0s, but show no strong trends with environment.

We present new Hubble Space Telescope/Wide Field Camera 3 imaging data of RCSGA 032727-132609, a bright lensed galaxy at z = 1.7 that is magnified and stretched by the lensing cluster RCS2 032727-132623. Using this new high-resolution imaging, we modify our previous lens model (which was based on ground-based data) to fully understand the lensing geometry, and use it to reconstruct the lensed galaxy in the source plane. This giant arc represents a unique opportunity to peer into 100 pc scale structures in a high-redshift galaxy. This new source reconstruction will be crucial for a future analysis of the spatially resolved rest-UV and rest-optical spectra of the brightest parts of the arc.

The presence of extremely compact galaxies at z ∼ 2 and their subsequent growth in physical size has been the cause of much puzzlement. We revisit the question using deep infrared Wide Field Camera 3 data to probe the rest-frame optical structure of 935 galaxies selected with 0.4 < z < 2.5 and stellar masses M_* > 10^10.7 M_☉ in the UKIRT Ultra Deep Survey and GOODS-South fields of the CANDELS survey. At each redshift, the most compact sources are those with little or no star formation, and the mean size of these systems at fixed stellar mass grows by a factor of 3.5 ± 0.3 over this redshift interval. The data are sufficiently deep to identify companions to these hosts whose stellar masses are ten times smaller. By searching for these around 404 quiescent hosts within a physical annulus 10 h⁻¹ kpc < R < 30 h⁻¹ kpc, we estimate the minor merger rate over 0.4 < z < 2. We find that 13%–18% of quiescent hosts have likely physical companions with stellar mass ratios of 0.1 or greater. Mergers of these companions will typically increase the host mass by 6% ± 2% per merger timescale. We estimate the minimum growth rate necessary to explain the declining abundance of compact galaxies. Using a simple model motivated by recent numerical simulations, we then assess whether mergers of the faint companions with their hosts are sufficient to explain this minimal rate. We find that mergers may explain most of the size evolution observed at z ≲ 1 if a relatively short merger timescale is assumed, but the rapid growth seen at higher redshift likely requires additional physical processes.

We describe the Multi-Epoch Nearby Cluster Survey, designed to measure the cluster Type Ia supernova (SN Ia) rate in a sample of 57 X-ray selected galaxy clusters, with redshifts of 0.05 < z < 0.15. Utilizing our real-time analysis pipeline, we spectroscopically confirmed twenty-three cluster SNe Ia, four of which were intracluster events. Using our deep Canada–France–Hawaii Telescope/MegaCam imaging, we measured total stellar luminosities in each of our galaxy clusters, and we performed detailed supernova (SN) detection efficiency simulations. Bringing these ingredients together, we measure an overall cluster SN Ia rate within R₂₀₀ (1 Mpc) of 0.042^+0.012_{− 0.010}^+0.010_{− 0.008} SNuM (0.049^+0.016_{− 0.014}^+0.005_{− 0.004} SNuM) and an SN Ia rate within red-sequence galaxies of 0.041^+0.015_{− 0.015}^+0.005_{− 0.010} SNuM (0.041^+0.019_{− 0.015}^+0.005_{− 0.004} SNuM). The red-sequence SN Ia rate is consistent with published rates in early-type/elliptical galaxies in the "field." Using our red-sequence SN Ia rate, and other cluster SN measurements in early-type galaxies up to z ∼ 1, we derive the late-time (>2 Gyr) delay time distribution (DTD) of SN Ia assuming a cluster early-type galaxy star formation epoch of z_f = 3. Assuming a power-law form for the DTD, Ψ(t)∝t^s, we find s = −1.62 ± 0.54. This result is consistent with predictions for the double degenerate SN Ia progenitor scenario (s ∼ −1) and is also in line with recent calculations for the double detonation explosion mechanism (s ∼ −2). The most recent calculations of the single degenerate scenario DTD predicts an order-of-magnitude drop-off in SN Ia rate ∼6–7 Gyr after stellar formation, and the observed cluster rates cannot rule this out.

We study effects of particle re-acceleration (or heating) in the post-shock region via magnetohydrodynamic/plasma turbulence, in the context of a mixed hadronic–leptonic model for the prompt emission of gamma-ray bursts, using both analytical and numerical methods. We show that stochastically accelerated (or heated) leptons, which are injected via pp and pγ reactions and subsequent pair cascades, are plausibly able to reproduce the Band function spectra with α ∼ 1 and β ∼ 2–3 in the ∼MeV range. An additional hard component coming from the proton-induced cascade emission is simultaneously expected, which can be compatible with observed extra power-law spectra far above the MeV range. We also discuss the specific implications of hadronic models for ongoing high-energy neutrino observations.

We have discovered 10 periodic X-ray sources from the 1 Ms Chandra ACIS observation of the Limiting Window (LW), a low-extinction region (A_V ∼ 3.9) at 14 south of the Galactic center. The observed periods (∼1.3–3.4 hr) and the X-ray luminosities (10^31.8–32.9 erg s⁻¹ at 8 kpc) of the 10 periodic sources, combined with the lack of bright optical counterparts and thus high X-ray-to-optical flux ratios, suggest that they are likely accreting binaries, in particular, magnetic cataclysmic variables (MCVs). All of them exhibit a relatively hard X-ray spectrum (Γ < 2 for a power-law model), and relatively high extinction observed in the X-ray spectra of at least five sources indicates some intrinsic absorption in the system, which is also a typical sign of MCVs. On close inspection, the period distribution of these sources resembles those of polars, whereas the relatively hard spectra suggest that they could be intermediate polars (IPs). These puzzling properties can be explained by unusual polars with buried magnetic fields or a rare sub-class of MCVs, nearly synchronous MCVs. These unusual MCVs may provide important clues in the evolutionary path of MCVs from IPs to polars. The completeness simulation indicates that ≳40% of the hard X-ray sources in the LW are periodic. Therefore, this discovery provides a first direct evidence of a large MCV population in the bulge and further supports the current view that MCVs constitute the majority of low-luminosity hard X-ray sources (∼10^30–33 erg s⁻¹) in the bulge.

The warm–hot intergalactic medium (WHIM) at temperatures 10⁵–10⁷ K is believed to contain 30%–50% of the baryons in the local universe. However, all current X-ray detections of the WHIM at redshifts z > 0 are of low statistical significance (≲ 3σ) and/or controversial. In this work, we aim to establish the detection limits of current X-ray observatories and explore requirements for next-generation X-ray telescopes for studying the WHIM through X-ray absorption lines. We analyze all available grating observations of Mrk 421 and obtain spectra with signal-to-noise ratios (S/Ns) of ∼90 and 190 per 50 mÅ spectral bin from Chandra and XMM-Newton observations, respectively. Although these spectra are two of the best ever collected with Chandra and XMM-Newton, we cannot confirm the two WHIM systems reported by Nicastro et al. in 2005. Our bootstrap simulations indicate that spectra with such high S/N cannot constrain the WHIM with O vii column densities $N_{{\rm O\,\mathsc{vii}}}\approx 10^{15} \,{\rm cm^{-2}}$ (corresponding to an equivalent width of 2.5 mÅ for a Doppler velocity of 50 km s⁻¹) at ≳ 3σ significance level. The simulation results also suggest that it would take >60 Ms for Chandra and 140 Ms for XMM-Newton to measure the $N_{{\rm O\,\mathsc{vii}}}$ at ⩾4σ from a spectrum of a background QSO with flux of ∼0.2 mCrab (1 Crab = 2 × 10⁻⁸ erg s⁻¹ cm⁻² at 0.5–2 keV). Future X-ray spectrographs need to be equipped with spectral resolution R ∼ 4000 and effective area A ⩾ 100 cm² to accomplish the similar constraints with an exposure time of ∼2 Ms and would require ∼11 Ms to survey the 15 QSOs with flux ≳ 0.2 mCrab along which clear intergalactic O vi absorbers have been detected.

NGC 326 is one of the most prominent "X"- or "Z"-shaped radio galaxies (XRGs/ZRGs) and has been the subject of several studies attempting to explain its morphology through either fluid motions or reorientation of the jet axis. We examine a 100 ks Chandra X-Ray Observatory exposure and find several features associated with the radio galaxy: a high-temperature front that may indicate a shock, high-temperature knots around the rim of the radio emission, and a cavity associated with the eastern wing of the radio galaxy. A reasonable interpretation of these features in light of the radio data allows us to reconstruct the history of the active galactic nucleus (AGN) outbursts. The active outburst was likely once a powerful radio source which has since decayed, and circumstantial evidence favors reorientation as the means to produce the wings. Because of the obvious interaction between the radio galaxy and the intracluster medium and the wide separation between the active lobes and wings, we conclude that XRGs are excellent sources in which to study AGN feedback in galaxy groups by measuring the heating rates associated with both active and passive heating mechanisms.

We present estimates of black hole accretion rates (BHARs) and nuclear, extended, and total star formation rates for a complete sample of Seyfert galaxies. Using data from the Spitzer Space Telescope, we measure the active galactic nucleus (AGN) luminosity using the [O iv] λ25.89 μm emission line and the star-forming luminosity using the 11.3 μm aromatic feature and extended 24 μm continuum emission. We find that black hole growth is strongly correlated with nuclear (r < 1 kpc) star formation, but only weakly correlated with extended (r > 1 kpc) star formation in the host galaxy. In particular, the nuclear star formation rate (SFR) traced by the 11.3 μm aromatic feature follows a relationship with the BHAR of the form ${\rm SFR}\propto \dot{M}_{{\rm BH}}^{0.8}$, with an observed scatter of 0.5 dex. This SFR–BHAR relationship persists when additional star formation in physically matched r = 1 kpc apertures is included, taking the form ${\rm SFR}\propto \dot{M}_{{\rm BH}}^{0.6}$. However, the relationship becomes almost indiscernible when total SFRs are considered. This suggests a physical connection between the gas on sub-kiloparsec and sub-parsec scales in local Seyfert galaxies that is not related to external processes in the host galaxy. It also suggests that the observed scaling between star formation and black hole growth for samples of AGNs will depend on whether the star formation is dominated by a nuclear or an extended component. We estimate the integrated black hole and bulge growth that occurs in these galaxies and find that an AGN duty cycle of 5%–10% would maintain the ratio between black hole and bulge masses seen in the local universe.

We jointly constrain the luminosity function (LF) and black hole mass function (BHMF) of broad-line quasars with forward Bayesian modeling in the quasar mass–luminosity plane, based on a homogeneous sample of ∼58, 000 Sloan Digital Sky Survey (SDSS) Data Release 7 quasars at z ∼ 0.3–5. We take into account the selection effect of the sample flux limit; more importantly, we deal with the statistical scatter between true BH masses and FWHM-based single-epoch virial mass estimates, as well as potential luminosity-dependent biases of these mass estimates. The LF is tightly constrained in the regime sampled by SDSS and makes reasonable predictions when extrapolated to ∼3 mag fainter. Downsizing is seen in the model LF. On the other hand, we find it difficult to constrain the BHMF to within a factor of a few at z ≳ 0.7 (with Mg ii and C iv-based virial BH masses). This is mainly driven by the unknown luminosity-dependent bias of these mass estimators and its degeneracy with other model parameters, and secondly driven by the fact that SDSS quasars only sample the tip of the active BH population at high redshift. Nevertheless, the most likely models favor a positive luminosity-dependent bias for Mg ii and possibly for C iv, such that at fixed true BH mass, objects with higher-than-average luminosities have overestimated FWHM-based virial masses. There is tentative evidence that downsizing also manifests itself in the active BHMF, and the BH mass density in broad-line quasars contributes an insignificant amount to the total BH mass density at all times. Within our model uncertainties, we do not find a strong BH mass dependence of the mean Eddington ratio, but there is evidence that the mean Eddington ratio (at fixed BH mass) increases with redshift.

As the number of observed gamma-ray bursts (GRBs) continues to grow, follow-up resources need to be used more efficiently in order to maximize science output from limited telescope time. As such, it is becoming increasingly important to rapidly identify bursts of interest as soon as possible after the event, before the afterglows fade beyond detectability. Studying the most distant (highest redshift) events, for instance, remains a primary goal for many in the field. Here, we present our Random Forest Automated Triage Estimator for GRB redshifts (RATE GRB-z) for rapid identification of high-redshift candidates using early-time metrics from the three telescopes onboard Swift. While the basic RATE methodology is generalizable to a number of resource allocation problems, here we demonstrate its utility for telescope-constrained follow-up efforts with the primary goal to identify and study high-z GRBs. For each new GRB, RATE GRB-z provides a recommendation—based on the available telescope time—of whether the event warrants additional follow-up resources. We train RATE GRB-z using a set consisting of 135 Swift bursts with known redshifts, only 18 of which are z > 4. Cross-validated performance metrics on these training data suggest that ∼56% of high-z bursts can be captured from following up the top 20% of the ranked candidates, and ∼84% of high-z bursts are identified after following up the top ∼40% of candidates. We further use the method to rank 200 + Swift bursts with unknown redshifts according to their likelihood of being high-z.

The current dynamical structure of the Kuiper Belt was shaped by the orbital evolution of the giant planets, especially Neptune, during the era following planet formation when the giant planets may have undergone planet–planet scattering and/or planetesimal-driven migration. Numerical simulations of this process, while reproducing many properties of the Belt, fail to generate the high inclinations and eccentricities observed for some objects while maintaining the observed dynamically "cold" population. We present the first of a three-part parameter study of how different dynamical histories of Neptune sculpt the planetesimal disk. Here we identify which dynamical histories allow an in situ planetesimal disk to remain dynamically cold, becoming today's cold Kuiper Belt population. We find that if Neptune undergoes a period of elevated eccentricity and/or inclination, it secularly excites the eccentricities and inclinations of the planetesimal disk. We demonstrate that there are several well-defined regimes for this secular excitation, depending on the relative timescales of Neptune's migration, the damping of Neptune's orbital inclination and/or eccentricity, and the secular evolution of the planetesimals. We model this secular excitation analytically in each regime, allowing for a thorough exploration of parameter space. Neptune's eccentricity and inclination can remain high for a limited amount of time without disrupting the cold classical belt. In the regime of slow damping and slow migration, if Neptune is located (for example) at 20 AU, then its eccentricity must stay below 0.18 and its inclination below 6°.

Baryon acoustic oscillations (BAOs) are a feature imprinted in the galaxy distribution by acoustic waves traveling in the plasma of the early universe. Their detection at the expected scale in large-scale structures strongly supports current cosmological models with a nearly linear evolution from redshift z ≈ 1000 and the existence of dark energy. In addition, BAOs provide a standard ruler for studying cosmic expansion. In this paper, we focus on methods for BAO detection using the correlation function measurement $\hat{\xi }$. For each method, we want to understand the tested hypothesis (the hypothesis $\mathcal {H}_0$ to be rejected) and the underlying assumptions. We first present wavelet methods which are mildly model-dependent and mostly sensitive to the BAO feature. Then we turn to fully model-dependent methods. We present the method used most often based on the χ² statistic, but we find that it has limitations. In general the assumptions of the χ² method are not verified, and it only gives a rough estimate of the significance. The estimate can become very wrong when considering more realistic hypotheses, where the covariance matrix of $\hat{\xi }$ depends on cosmological parameters. Instead, we propose to use the Δl method based on two modifications: we modify the procedure for computing the significance and make it rigorous, and we modify the statistic to obtain better results in the case of varying covariance matrix. We verify with simulations that correct significances are different from the ones obtained using the classical χ² procedure. We also test a simple example of varying covariance matrix. In this case we find that our modified statistic outperforms the classical χ² statistic when both significances are correctly computed. Finally, we find that taking into account variations of the covariance matrix can change both BAO detection levels and cosmological parameter constraints.

Using high-resolution ultraviolet spectra obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph and the Far Ultraviolet Spectroscopic Explorer, we study the metallicity, kinematics, and distance of the gaseous "outer arm" (OA) and the high-velocity clouds (HVCs) in the outer Galaxy. We detect the OA in a variety of absorption lines toward two QSOs, H1821+643 and HS0624+6907. We search for OA absorption toward eight Galactic stars and detect it in one case, which constrains the OA Galactocentric radius to 9 kpc <R_G < 18 kpc. We also detect HVC Complex G, which is projected near the OA at a similar velocity, in absorption toward two stars; Complex G is therefore in the same region at R_G = 8–10 kpc. HVC Complex C is known to be at a similar Galactocentric radius. Toward H1821+643, the low-ionization absorption lines are composed of multiple narrow components, indicating the presence of several cold clouds and rapid cooling and fragmentation. Some of the highly ionized gas is also surprisingly cool. Accounting for ionization corrections, we find that the OA metallicity is Z = 0.2–0.5 Z_☉, but nitrogen is underabundant and some species are possibly mildly depleted by dust. The similarity of the OA metallicity, Galactocentric location, and kinematics to those of the adjacent outer-Galaxy HVCs, including high velocities that are not consistent with Galactic rotation, suggests that the OA and outer-Galaxy HVCs could have a common origin.

Infrared-dark clouds (IRDCs) are believed to be the birthplaces of rich clusters and thus contain the earliest phases of high-mass star formation. We use the Green Bank Telescope and Very Large Array maps of ammonia (NH₃) in six IRDCs to measure their column density and temperature structure (Paper 1), and here, we investigate the kinematic structure and energy content. We find that IRDCs overall display organized velocity fields, with only localized disruptions due to embedded star formation. The local effects seen in NH₃ emission are not high-velocity outflows but rather moderate (few km s⁻¹) increases in the linewidth that exhibit maxima near or coincident with the mid-infrared emission tracing protostars. These linewidth enhancements could be the result of infall or (hidden in NH₃ emission) outflow. Not only is the kinetic energy content insufficient to support the IRDCs against collapse, but also the spatial energy distribution is inconsistent with a scenario of turbulent cloud support. We conclude that the velocity signatures of the IRDCs in our sample are due to active collapse and fragmentation, in some cases augmented by local feedback from stars.

Vacuum–ultraviolet light from a synchrotron was applied to record absorption spectra in the region of 105–170 nm with a resolution of 0.2 nm and for the photolysis of pure solid N₂ and CH₄ dispersed in solid N₂ (CH₄/N₂ = 1/100 for absorption and 1/500 for photolysis) at 20 K. After photolysis of the icy samples at wavelengths 130 nm (9.5 eV), 121.6 nm (10.2 eV), and 91.6 nm (13.5 eV), infrared absorption features of products N₃, C_nN (n = 1–3), CN₂, (CN)₂, HCN₂, HC₂N, C(NH)₂, HN₃, HNC, HCN, HCCNH⁺, and NCCN⁺ were identified. We investigated the dependence on wavelength of the formation of these products and their column densities of formation. We also studied the ratio of the column densities of HCN and HNC as a function of photolysis wavelength and duration of irradiation. The mechanisms of formation of the main products are discussed. Our results have implications for the radiatively assisted syntheses of nitrile molecules in the interstellar medium and on icy surfaces of planets and satellites in the solar system.

Numerical relativity simulations predict that coalescence of supermassive black hole (SMBH) binaries leads not only to a spin flip but also to a recoiling of the merger remnant SMBHs. In the literature, X-shaped radio sources are popularly suggested to be candidates for SMBH mergers with spin flip of jet-ejecting SMBHs. Here we investigate the spectral and spatial observational signatures of the recoiling SMBHs in radio sources undergoing black hole spin flip. Our results show that SMBHs in most spin-flip radio sources have mass ratio q ≳ 0.3 with a minimum possible value q_min ≃ 0.05. For major mergers, the remnant SMBHs can get a kick velocity as high as 2100 km s⁻¹ in the direction within an angle ≲ 40° relative to the spin axes of remnant SMBHs, implying that recoiling quasars are biased to be with high Doppler-shifted broad emission lines while recoiling radio galaxies are biased to large apparent spatial off-center displacements. We also calculate the distribution functions of line-of-sight velocity and apparent spatial off-center displacements for spin-flip radio sources with different apparent jet reorientation angles. Our results show that the larger the apparent jet reorientation angle is, the larger the Doppler-shifting recoiling velocity and apparent spatial off-center displacement will be. We investigate the effects of recoiling velocity on the dust torus in spin-flip radio sources and suggest that recoiling of SMBHs would lead to "dust-poor" active galactic nuclei. Finally, we collect a sample of 19 X-shaped radio objects and for each object give the probability of detecting the predicted signatures of recoiling SMBH.

M87 is the first detected non-blazar extragalactic tera-electron-volt (TeV) source with rapid variation and a very flat spectrum in the TeV band. To explain the two peaks in the spectral energy distribution of the nucleus of M87, which is similar to that of blazars, the most commonly adopted models are the synchrotron self-Compton-scattering models and the external inverse Compton (EIC) scattering models. Considering that there is no correlated variation in the soft band (from radio to X-ray) matching the TeV variation and that the TeV sources should not suffer from γγ absorption due to the flat TeV spectrum, the EIC models are advantageous in modeling the TeV emission from M87. In this paper, we propose a self-consistent EIC model to explain the flat TeV spectrum of M87 within the framework of fully general relativity, where the background soft photons are from the advection-dominated accretion flow around the central black hole, and the high-energy electrons are from the mini-jets that are powered by the magnetic reconnection in the main jet. In our model, both the TeV flares observed in the years 2005 and 2008 could be well explained: the γγ absorption for TeV photons is very low, even inside the region very close to the black hole 20R_g ∼ 50R_g; at the same region, the average EIC cooling time (∼10²  ∼  10³ s) is short, which is consistent with the observed timescale of the TeV variation. Furthermore, we also discuss the possibility that the accompanying X-ray flare in 2008 is due to the direct synchrotron radiation of the mini-jets.

Reducing the scatter between cluster mass and optical richness is a key goal for cluster cosmology from photometric catalogs. We consider various modifications to the red-sequence-matched filter richness estimator of Rozo et al. implemented on the maxBCG cluster catalog and evaluate the impact of these changes on the scatter in X-ray luminosity (L_X) at fixed richness, using L_X from the ROSAT All-Sky Catalog as the best mass proxy available for the large area required. Most significantly, we find that deeper luminosity cuts can reduce the recovered scatter, finding that $\sigma _{\ln L_X|\lambda }=0.63\pm 0.02$ for clusters with M_500c ≳ 1.6 × 10¹⁴ h⁻¹₇₀ M_☉. The corresponding scatter in mass at fixed richness is σ_ln M|λ ≈ 0.2–0.3 depending on the richness, comparable to that for total X-ray luminosity. We find that including blue galaxies in the richness estimate increases the scatter, as does weighting galaxies by their optical luminosity. We further demonstrate that our richness estimator is very robust. Specifically, the filter employed when estimating richness can be calibrated directly from the data, without requiring a priori calibrations of the red sequence. We also demonstrate that the recovered richness is robust to up to 50% uncertainties in the galaxy background, as well as to the choice of photometric filter employed, so long as the filters span the 4000 Å break of red-sequence galaxies. Consequently, our richness estimator can be used to compare richness estimates of different clusters, even if they do not share the same photometric data. Appendix A includes "easy-bake" instructions for implementing our optimal richness estimator, and we are releasing an implementation of the code that works with Sloan Digital Sky Survey data, as well as an augmented maxBCG catalog with the λ richness measured for each cluster.

Reports of the death of the precursor of supernova (SN) 1961V in NGC 1058 are exaggerated. Consideration of the best astrometric data shows that the star, known as "Object 7," lies at the greatest proximity to SN 1961V and is the likely survivor of the "SN impostor" super-outburst. SN 1961V does not coincide with a neighboring radio source and is therefore not a radio SN. Additionally, the current properties of Object 7, based on data obtained with the Hubble Space Telescope, are consistent with it being a quiescent luminous blue variable (LBV). Furthermore, post-explosion non-detections by the Spitzer Space Telescope do not necessarily and sufficiently rule out a surviving LBV. We therefore consider, based on the available evidence, that it is still a bit premature to reclassify SN 1961V as a bona fide SN. The inevitable demise of this star, though, may not be too far off.

We examine r-process nucleosynthesis in the neutrino-driven wind from the thick accretion disk (or "torus") around a black hole. Such systems are expected as remnants of binary neutron star or neutron star–black hole mergers. We consider a simplified, analytic, time-dependent evolution model of a 3 M_☉ central black hole surrounded by a neutrino emitting accretion torus with 90 km radius, which serves as basis for computing spherically symmetric neutrino-driven wind solutions. We find that ejecta with modest entropies (∼30 per nucleon in units of the Boltzmann constant) and moderate expansion timescales (∼100 ms) dominate in the mass outflow. The mass-integrated nucleosynthetic abundances are in good agreement with the solar system r-process abundance distribution if a minimal value of the electron fraction at the charged-particle freezeout, Y_{e, min} ∼ 0.2, is achieved. In the case of Y_{e, min} ∼ 0.3, the production of r-elements beyond A ∼ 130 does not reach to the third peak but could still be important for an explanation of the abundance signatures in r-process deficient stars in the early Galaxy. The total mass of the ejected r-process nuclei is estimated to be ∼1 × 10⁻³ M_☉. If our model was representative, this demands a Galactic event rate of ∼2 × 10⁻⁴ yr⁻¹ for black-hole-torus winds from merger remnants to be the dominant source of the r-process elements. Our result thus suggests that black-hole-torus winds from compact binary mergers have the potential to be a major, but probably not the dominant, production site of r-process elements.

We use the Stripe 82 proper-motion catalog of Bramich et al. to study the kinematics of Galactic disk stars in the solar neighborhood. We select samples of dwarf stars with reliable spectra and proper motions. They have cylindrical polar radii between 7 ⩽ R ⩽ 9 kpc, heights from the Galactic plane satisfying |z| ⩽ 2 kpc, and span a range of metallicities −1.5 ⩽ [Fe/H] ⩽ 0. We develop a method for calculating and correcting for the halo contamination in our sample using the distribution of rotational velocities. Two Gaussians representing disk and halo populations are used to fit the radial (v_R) and vertical (v_z) velocity distributions via maximum likelihood methods. For the azimuthal velocities (v_ϕ) the same technique is used, except that a skewed non-Gaussian functional form now represents the disk velocity distribution. This enables us to compute the dispersions σ_R, σ_z, σ_ϕ, and cross-terms (the tilt σ_Rz and the vertex deviation σ_Rϕ) of the velocity ellipsoid as a function of height and metallicity. We also investigate the rotation lag of the disk, finding that the more metal-poor stars rotate significantly slower than the metal-rich stars. These samples provide important constraints on heating mechanisms in the Galactic disk and can be used for a variety of applications. We present one such application employing the Jeans equations to provide a simple model of the potential close to the disk. Our model is in excellent agreement with others in the literature and provides an indication that the disk, rather than the halo, dominates the circular speed at the solar neighborhood. We obtain a surface mass density within 1.1 kpc of around 66 M_☉ pc⁻² and estimate a local halo density of 0.015 M_☉ pc⁻³ = 0.57 GeV cm⁻³.

This paper presents results from the analysis of high signal-to-noise ratio spectropolarimetric data taken at four heliocentric angles in quiet-Sun internetwork regions with the Hinode satellite. First, we find that the total circular and total linear polarization signals vary with heliocentric angle, at least for fields with large polarization signals. We also report changes on the Stokes V amplitude asymmetry histograms with viewing angle for fields weaker than 200 G. Then, we subject the data to a Milne–Eddington inversion and analyze the variation of the field vector probability density functions with heliocentric angle. Weak, highly inclined fields permeate the internetwork at all heliocentric distances. For fields weaker than 200 G, the distributions of field inclinations peak at 90° and do not vary with viewing angle. The inclination distributions change for fields stronger than 200 G. We argue that the shape of the inclination distribution for weak fields partly results from the presence of coherent, loop-like magnetic features at all heliocentric distances and not from tangled fields within the field of view. We also find that the average magnetic field strength is about 180 G (for 75% of the pixels) and is constant with heliocentric angle. The average vertical and horizontal magnetic field components are 70 and 150 G. The latter (former) is slightly greater (smaller) near the limb. Finally, the ratio between the horizontal and vertical components of the fields ranges from ∼1 for strong fields to ∼3.5 for weak fields, suggesting that the magnetic field vector is not isotropically distributed within the field of view.

We present high-cadence observations and simulations of the solar photosphere, obtained using the Rapid Oscillations in the Solar Atmosphere imaging system and the MuRAM magnetohydrodynamic (MHD) code, respectively. Each data set demonstrates a wealth of magnetoacoustic oscillatory behavior, visible as periodic intensity fluctuations with periods in the range 110–600 s. Almost no propagating waves with periods less than 140 s and 110 s are detected in the observational and simulated data sets, respectively. High concentrations of power are found in highly magnetized regions, such as magnetic bright points and intergranular lanes. Radiative diagnostics of the photospheric simulations replicate our observational results, confirming that the current breed of MHD simulations are able to accurately represent the lower solar atmosphere. All observed oscillations are generated as a result of naturally occurring magnetoconvective processes, with no specific input driver present. Using contribution functions extracted from our numerical simulations, we estimate minimum G-band and 4170 Å continuum formation heights of 100 km and 25 km, respectively. Detected magnetoacoustic oscillations exhibit a dominant phase delay of −8° between the G-band and 4170 Å continuum observations, suggesting the presence of upwardly propagating waves. More than 73% of MBPs (73% from observations and 96% from simulations) display upwardly propagating wave phenomena, suggesting the abundant nature of oscillatory behavior detected higher in the solar atmosphere may be traced back to magnetoconvective processes occurring in the upper layers of the Sun's convection zone.

We investigate a class of axisymmetric magnetohydrodynamic turbulence which satisfies the exact relation for third-order Elsässer structure functions. Following the critical balance conjecture, we assume the existence of a power-law relation between correlation length scales along and transverse to the local mean magnetic field direction. The flow direction of the vector third-order moments F^± is then along axisymmetric concave/convex surfaces, the axis of symmetry being given by the mean magnetic field. Under this consideration, the vector F^± satisfies a simple Kolmogorov law which depends on the anisotropic parameter a^±, which measures the concavity of the surfaces. A comparison with recent in situ multispacecraft solar wind observations is made; it is concluded that the underlying turbulence is very likely convex. A discussion is given about the physical meaning of such an anisotropy.

We present seven newly discovered non-eclipsing short-period binary systems with low-mass companions, identified by the recently introduced BEER algorithm, applied to the publicly available 138-day photometric light curves obtained by the Kepler mission. The detection is based on the beaming effect (sometimes called Doppler boosting), which increases (decreases) the brightness of any light source approaching (receding from) the observer, enabling a prediction of the stellar Doppler radial-velocity (RV) modulation from its precise photometry. The BEER algorithm identifies the BEaming periodic modulation, with a combination of the well-known Ellipsoidal and Reflection/heating periodic effects, induced by short-period companions. The seven detections were confirmed by spectroscopic RV follow-up observations, indicating minimum secondary masses in the range 0.07–0.4 M_☉. The binaries discovered establish for the first time the feasibility of the BEER algorithm as a new detection method for short-period non-eclipsing binaries, with the potential to detect in the near future non-transiting brown-dwarf secondaries, or even massive planets.

Binaries that contain a hot subdwarf (sdB) star and a main-sequence companion may have interacted in the past. This binary population has historically helped determine our understanding of binary stellar evolution. We have computed a grid of binary population synthesis models using different assumptions about the minimum core mass for helium ignition, the envelope binding energy, the common-envelope ejection efficiency, the amount of mass and angular momentum lost during stable mass transfer, and the criteria for stable mass transfer on the red giant branch and in the Hertzsprung gap. These parameters separately and together can significantly change the entire predicted population of sdBs. Nonetheless, several different parameter sets can reproduce the observed subpopulation of sdB + white dwarf and sdB + M dwarf binaries, which has been used to constrain these parameters in previous studies. The period distribution of sdB + early F dwarf binaries offers a better test of different mass transfer scenarios for stars that fill their Roche lobes on the red giant branch.

We present high angular resolution continuum observations of the high-mass protostar NGC 7538 S with BIMA and CARMA at 3 and 1.4 mm, Very Large Array (VLA) observations at 1.3, 2, 3.5, and 6 cm, and archive Infrared Array Camera (IRAC) observations from the Spitzer Space Observatory, which detect the star at 4.5, 5.8, and 8 μm. The star looks rather unremarkable in the mid-IR. The excellent positional agreement of the IRAC source with the VLA free–free emission, the OH, CH₃OH, H₂O masers, and the dust continuum confirms that this is the most luminous object in the NGC 7538 S core. The continuum emission at millimeter wavelengths is dominated by dust emission from the dense cold cloud core surrounding the protostar. Including all array configurations, the emission is dominated by an elliptical source with a size of ∼8'' × 3''. If we filter out the extended emission we find three compact millimeter sources inside the elliptical core. The strongest one, S_A, coincides with the VLA/IRAC source and resolves into a double source at 1.4 mm, where we have subarcsecond resolution. The measured spectral index, α, between 3 and 1.4 mm is ∼2.3, and steeper at longer wavelengths, suggesting a low dust emissivity or that the dust is optically thick. We argue that the dust in these accretion disks is optically thick and estimate a mass of an accretion disk or infalling envelope surrounding S_A to be ∼60 M_☉.

We evaluate the effects of environment and stellar mass on galaxy properties at 0.85 <z < 1.20 using a 3.6 μm-selected spectroscopic sample of 797 cluster and field galaxies drawn from the Gemini Cluster Astrophysics Spectroscopic Survey. We confirm that for galaxies with log M_*/M_☉ > 9.3 the well-known correlations between environment and properties such as star-forming fraction (f_SF), star formation rate (SFR), specific SFR (SSFR), D_n(4000), and color are already in place at z ∼ 1. We separate the effects of environment and stellar mass on galaxies by comparing the properties of star-forming and quiescent galaxies at fixed environment and fixed stellar mass. The SSFR of star-forming galaxies at fixed environment is correlated with stellar mass; however, at fixed stellar mass it is independent of environment. The same trend exists for the D_n(4000) measures of both the star-forming and quiescent galaxies and shows that their properties are determined primarily by their stellar mass, not by their environment. Instead, it appears that environment's primary role is to control the fraction of star-forming galaxies. Using the spectra we identify candidate poststarburst galaxies and find that those with 9.3 < log M_*/M_☉ < 10.7 are 3.1 ± 1.1 times more common in high-density regions compared to low-density regions. The clear association of poststarbursts with high-density regions as well as the lack of a correlation between the SSFRs and D_n(4000)s of star-forming galaxies with their environment strongly suggests that at z ∼ 1 the environmental-quenching timescale must be rapid. Lastly, we construct a simple quenching model which demonstrates that the lack of a correlation between the D_n(4000) of quiescent galaxies and their environment results naturally if self quenching dominates over environmental quenching at z > 1, or if the evolution of the self-quenching rate mirrors the evolution of the environmental-quenching rate at z > 1, regardless of which dominates.

A study is made of deviations from the mean power-law relationship between the Galactocentric distances and the half-light radii of Galactic globular clusters. Surprisingly, deviations from the mean R_h versus R_gc relationship do not appear to correlate with cluster luminosity, cluster metallicity, or horizontal-branch morphology. Differences in orbit shape are found to contribute to the scatter in the R_h versus R_gc relationship of Galactic globular clusters.