Table of contents

It has been widely shown that cosmological parameters and dark energy can be constrained by using data from Type Ia supernovae (SNe Ia), the cosmic microwave background (CMB) anisotropy, the baryon acoustic oscillation (BAO) peak from Sloan Digital Sky Survey (SDSS), the X-ray gas mass fraction in clusters, and the linear growth rate of perturbations at z = 0.15 as obtained from the 2dF Galaxy Redshift Survey. Recently, gamma-ray bursts (GRBs) have also been argued to be promising standard candles for cosmography. In this paper, we present constraints on the cosmological parameters and dark energy by combining a recent GRB sample including 69 events with the other cosmological probes. First, we find that for the ΛCDM cosmology this combination makes the constraints stringent, and the best fit is close to the flat universe. Second, we fit the flat Cardassian expansion model and find that this model is consistent with the ΛCDM cosmology. Third, we present constraints on several two-parameter dark energy models and find that these models are also consistent with the ΛCDM cosmology. Finally, we reconstruct the dark energy equation of state parameter w(z) and the deceleration parameter q(z). We see that the acceleration could have started at a redshift from z_t = 0.40 to 0.65. This difference in the transition redshift is due to different dark energy models that we adopt. The most stringent constraint on w(z) lies in the redshift range z ~ 0.3-0.6.

Determination of the cosmic infrared background (CIB) at far-infrared wavelengths using COBE DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Most previous determinations of the far-infrared CIB were based on the detection of residual isotropic emission in sky maps from which the emission from interplanetary dust and the neutral interstellar medium were removed. In this paper we use the Wisconsin Hα Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose DIRBE far-infrared data for five high Galactic latitude regions into H I- and Hα-correlated components and a residual component. We find the Hα-correlated component to be consistent with zero for each region, yielding CIB results that are essentially the same as those previously derived by the COBE DIRBE team: νI_ν(nW m^-2 sr^-1) < 75, <32, =25 ± 8, and =13 ± 3 at 60, 100, 140, and 240 μm, respectively (upper limits are 2 σ). For comparison, the estimated integrated light from galaxies based on Spitzer 160 μm source counts is 13.7 ± 1.7 and 10.7 ± 1.4 nW m^-2 sr^-1 at 140 and 240 μm, respectively. We derive upper limits on the 100 μm emissivity of the ionized medium that are typically about 40% of the 100 μm emissivity of the neutral atomic medium. If Hα is not a reliable tracer of far-infrared emission, we show that our analysis would underestimate the emissivity of the ionized medium and could slightly overestimate the CIB.

The main uncertainty in current determinations of the power spectrum normalization, σ₈, from abundances of X-ray-luminous galaxy clusters arises from the calibration of the mass-temperature relation. We use our weak-lensing mass determinations of 30 clusters from the hitherto largest sample of clusters with lensing masses, combined with X-ray temperature data from the literature, to calibrate the normalization of this relation at a temperature of 8 keV, M_{500c, 8 keV} = (8.7 ± 1.6) h^-1 10¹⁴M_☉. This normalization is consistent with previous lensing-based results based on smaller cluster samples, and with some predictions from numerical simulations, but higher than most normalizations based on X-ray-derived cluster masses. Assuming the theoretically expected slope α = 3/2 of the mass-temperature relation, we derive σ₈ = 0.88 ± 0.09 for a spatially flat ΛCDM universe with Ω_m = 0.3. The main systematic errors on the lensing masses result from extrapolating the cluster masses beyond the field of view used for the gravitational lensing measurements, and from the separation of cluster/background galaxies, contributing each with a scatter of 20%. Taking this into account, there is still significant intrinsic scatter in the mass-temperature relation indicating that this relation may not be very tight, at least at the high-mass end. Furthermore, we find that dynamically relaxed clusters are (75 ± 40)% hotter than nonrelaxed clusters.

In this paper we derive semiempirical Cepheid period-luminosity (P-L) relations in the Sloan ugriz magnitudes by combining the observed BVI mean magnitudes from the Large Magellanic Cloud (LMC) Cepheids and theoretical bolometric corrections. We also constructed empirical gr band P-L relations, using the publicly available Johnson-Sloan photometric transformations, to be compared with our semiempirical P-L relations. These two sets of P-L relations are consistent with each other.

We discuss the link between dark matter halos hosting the first Population III stars and the rare, massive halos that are generally considered to host bright quasars at high redshift (z ≈ 6). The main question that we intend to answer is whether the supermassive black holes powering these QSOs grew out from the seeds planted by the first intermediate-mass black holes created in the universe. This question involves a dynamical range of 10¹³ in mass, and we address it by combining N-body simulations of structure formation to identify the most massive halos at z ≈ 6 with a Monte Carlo method based on linear theory to obtain the location and formation times of the first-light halos within the whole simulation box. We show that the descendants of the first ≈10⁶M_☉ virialized halos do not, on average, end in the most massive halos at z ≈ 6, but rather live in a large variety of environments. The oldest Population III progenitors of the most massive halos at z ≈ 6 form instead from density peaks that are on average 1.5 σ more common than the first Population III star formed in the volume occupied by one bright high-z QSO. The intermediate-mass black hole seeds planted by the very first Population III stars at z ≳ 40 can easily grow to masses m_BH > 10^9.5M_☉ by z = 6 assuming Eddington accretion with radiative efficiency ≲ 0.1. Quenching of the black hole accretion is therefore crucial to avoid an overabundance of supermassive black holes at lower redshift. This can be obtained if the mass accretion is limited to a fraction η ≈ 6 × 10^-3 of the total baryon mass of the halo hosting the black hole. The resulting high-end slope of the black hole mass function at z = 6 is α ≈ -3.7, a value within the 1 σ error bar for the bright-end slope of the observed quasar luminosity function at z = 6.

High-redshift galaxies selected on the basis of strong Lyα emission tend to be young and have small physical sizes. We show this by analyzing the spectral energy distribution of nine Lyα-emitting galaxies (LAEs) at 4.0 < z < 5.7 in the Hubble Ultra Deep Field. Rest-frame UV-to-optical (700 Å < λ < 7500 Å) luminosities, or upper limits, are used to constrain old stellar populations. We derive best-fit, as well as maximally massive and maximally old, properties of all nine objects. We show that these faint and distant objects are all very young, most likely only a few million years old, and not massive, the mass in stars being ≈10⁶-10⁸M_☉. Deep Spitzer Infrared Array Camera observations of these objects, even in cases where the object was not detected, proved crucial in constraining the masses of these objects. The space density of these objects, ≈1.25 × 10^-4 Mpc^-3, is comparable to previously reported space densities of LAEs at moderate-to-high redshifts. These Lyα galaxies show modest star formation rates of ≈8 M_☉ yr^-1, which is nevertheless strong enough to have allowed them to assemble their stellar mass in less than a few million years. These sources appear to have small physical sizes, usually smaller than 1 kpc, and are also rather concentrated. They are likely to be some of the least massive and youngest high-redshift galaxies observed to date.

We calculate the observable properties of the most massive high-redshift galaxies in the hierarchical formation scenario where stellar spheroid and supermassive black hole growth are fueled by gas-rich mergers. Combining high-resolution hydrodynamical simulations of the hierarchical formation of a z ~ 6 quasar, stellar population synthesis models, template active galactic nucleus (AGN) spectra, prescriptions for interstellar and intergalactic absorption, and the response of modern telescopes, the photometric evolution of galaxies destined to host z ~ 6 quasars is modeled at redshifts z ~ 4-14. These massive galaxies, with enormous stellar masses of M_⋆ ~ 10^11.5-10¹²M_☉ and star formation rates of SFR ~ 10³-10⁴M_☉ yr^-1 at z ≳ 7, satisfy a variety of photometric selection criteria based on Lyman break techniques, including V-band dropouts at z ≳ 5, i-band dropouts at z ≳ 6, and z-band dropouts at z ≳ 7. The observability of the most massive high-redshift galaxies is assessed and compared with a wide range of existing and proposed photometric surveys, including the Sloan Digital Sky Survey (SDSS), Great Observatories Origins Deep Survey (GOODS)/Hubble Ultra Deep Field (HUDF), National Optical Astronomy Observatory Deep Wide-Field Survey (NDWFS), UKIRT Infared Deep Sky Survey (UKIDSS), Infrared Array Camera (IRAC) Shallow Survey, Ultradeep Visible and Infrared Survey Telescope for Astronomy (VISTA), Dark Universe Explorer (DUNE), Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), Large Synoptic Survey Telescope (LSST), and Supernova/Acceleration Probe (SNAP). Massive stellar spheroids descended from z ~ 6 quasars will likely be detected at z ~ 4 by existing surveys, but owing to their low number densities the discovery of quasar progenitor galaxies at z > 7 will likely require future surveys of large portions of the sky (≳0.5%) at wavelengths λ ≳ 1 μm. The detection of rare, starbursting, massive galaxies at redshifts z ≳ 6 would provide support for the hierarchical formation of the earliest quasars and characterize the primitive star formation histories of the most luminous elliptical galaxies.

We describe the results of an extremely deep, 0.28 deg² survey for z = 3.1 Lyα emission-line galaxies in the Extended Chandra Deep Field-South. By using a narrowband 5000 Å filter and complementary broadband photometry from the MUSYC survey, we identify a statistically complete sample of 162 galaxies with monochromatic fluxes brighter than 1.5 × 10^-17 ergs cm^-2 s^-1 and observer's frame equivalent widths greater than 80 Å. We show that the equivalent width distribution of these objects follows an exponential with a rest-frame scale length of w₀ = 76 Å. In addition, we show that in the emission line, the luminosity function of Lyα galaxies has a faint-end power-law slope of α = -1.49, a bright-end cutoff of log L* = 42.64, and a space density above our detection thresholds of (1.46 ± 0.12) × 10^-3h galaxies Mpc^-3. Finally, by comparing the emission-line and continuum properties of the Lyα emitters, we show that the star formation rates derived from Lyα are ~3 times lower than those inferred from the rest-frame UV continuum. We use this offset to deduce the existence of a small amount of internal extinction within the host galaxies. This extinction, coupled with the lack of extremely high equivalent width emitters, argues that these galaxies are not primordial Population III objects, although they are young and relatively chemically unevolved.

We present a feedback compression model to describe galactic spheroid formation and its relation with the central nuclear activity. We suggest that the star formation itself can serve as the positive feedback in some extremely dense region to trigger the starburst. The star formation rate, as well as the related stellar feedback-induced turbulence, will be maximized under the regulation of the background dark halo's gravity. There is also stellar feedback acting inward to confine and obscure the central black hole (BH) until the BH grows sufficiently large to satisfy a balance condition between the accretion disk wind and the inward stellar feedback. The extremely vigorous star formation activity, the BH-bulge relations, the maximum velocity dispersion, and the maximum BH mass are investigated on the basis of such a scenario and are found to be consistent with observations.

We estimated black hole masses and Eddington ratios for a sample of X-ray-selected active galactic nuclei (AGNs) in the fields covered by the Great Observatory Origins Deep Survey (GOODS). The spanned ranges in redshift (0.4 < z < 1) and hard X-ray luminosity (10⁴² ≲ L_X ≲ 4 × 10⁴³ ergs s^-1) allow us to study a representative subsample of the main contributors to the 2-10 keV X-ray background. Nuclear and bulge magnitudes in four bands have been measured via a two-dimensional decomposition applied to HST ACS images. Using the black hole versus bulge luminosity relation and the intrinsic nuclear emission, we derived the black hole mass and the AGN bolometric luminosity. We find in our sample that (1) the X-ray-to-optical indices are larger than in optically selected QSOs, as expected due to the X-ray selection); (2) the X-ray bolometric corrections are generally small, suggesting a decrease with the nuclear luminosity; (3) the Eddington ratios are about a factor 10 below the values found at higher redshift and luminosity; (4) the central black holes have rather large masses; and (5) at least for z ≲ 0.8, a scarceness of black holes with mass M_BH ≤ 10⁶M_☉ and accretion rate near the Eddington limit: this result could be ascribed to a decline in their number density, or it could suggest a substantial accretion at higher redshift (z ≳ 1) also for these smaller black holes.

We use high-resolution images obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope to determine morphology, nuclear luminosity, and structural parameters of the spheroidal component for a sample of 20 Seyfert galaxies at z = 0.36. We combine these measurements with spectroscopic information from the Keck Telescope to determine the black hole mass-spheroid luminosity relation (M_BH-L_B), the fundamental plane (FP) of the host galaxies, and the black hole mass-spheroid velocity dispersion relation (M_BH-σ). The FP is consistent with that of inactive spheroids at comparable redshifts. Assuming pure luminosity evolution, we find that the host spheroids had smaller luminosity and stellar velocity dispersion than today for a fixed M_BH. The offsets correspond to Δ log L_B,0 = 0.40 ± 0.11 ± 0.15 (Δ log M_BH = 0.51 ± 0.14 ± 0.19) and Δ log σ = 0.13 ± 0.03 ± 0.05 (Δ log M_BH = 0.54 ± 0.12 ± 0.21), respectively, for the M_BH-L and M_BH-σ relations (the double error bars indicate random and systematic uncertainties, respectively). A detailed analysis of known systematic errors and selection effects shows that they cannot account for the observed offset. We conclude that the data are inconsistent with pure luminosity evolution and the existence of universal and tight scaling relations. In order to obey the three local scaling relations by z = 0, assuming no significant black hole growth, the distant spheroids have to grow their stellar mass by approximately 60% (Δ log M_sph = 0.20 ± 0.14) in the next 4 billion years, while preserving their size and holding their stellar mass-to-light ratio approximately constant. The measured evolution can be expressed as M_BH/M_sph ∝ (1 + z)^1.5±1.0, consistent with black holes of a few × 10⁸M_☉ completing their growth before their host galaxies. Based on the disturbed morphologies of a fraction of the sample (6/20), we suggest collisional mergers with disk-dominated systems as the physical mechanism driving the evolution.

We present the first measurement of the BH mass function for broad-line active galaxies in the local universe. Using the ~8500 broad-line active galaxies from SDSS DR4, we construct a broad-line luminosity function that agrees very well with the local soft X-ray luminosity function. Using standard virial relations, we then convert observed broad-line luminosities and widths into BH masses. A mass function constructed in this way has the unique capability to probe the mass region <10⁶M_☉, which, while insignificant in terms of total BH mass density, nevertheless may place important constraints on the mass distribution of seed BHs in the early universe. The characteristic local active BH has a mass of ~10⁷M_☉ radiating at 10% of the Eddington rate. The active fraction is a strong function of BH mass; at both higher and lower masses the active mass function falls more steeply than one would infer from the distribution of bulge luminosity. The deficit of local massive radiating BHs is a well-known phenomenon, while we present the first robust measurement of a decline in the space density of active BHs at low mass.

We present R ~ 600, 10-37 μm spectra of 53 ultraluminous infrared galaxies (ULIRGs), taken using the Infrared Spectrograph on board Spitzer. The spectra show fine-structure emission lines of neon, oxygen, sulfur, silicon, argon, chlorine, iron, and phosphorous; molecular hydrogen lines, and C₂H₂, HCN, and OH^- absorption features. We employ diagnostics based on the fine-structure lines, the polycyclic aromatic hydrocarbon (PAH) features and the 9.7 μm silicate absorption feature, to show that the infrared emission from most ULIRGs is powered mostly by star formation, with only ~20% of ULIRGs hosting an AGN with a greater IR luminosity than the starburst. The detection of [Ne V] λ14.32 in just under half the sample, however, implies that an AGN contributes significantly to the mid-IR flux in ~42% of ULIRGs. The starbursts and AGNs in ULIRGs appear more extincted, and for the starbursts more compact than those in lower luminosity systems. The excitations and electron densities in the narrow-line regions of ULIRGs appear comparable to those of starbursts with L≲10^11.5L_☉, although the NLR gas in ULIRGs may be more dense. We show that the [Ne II] λ12.81 + [Ne III] λ15.56 luminosity correlates with both infrared luminosity and the luminosity of the 6.2 and 11.2 μm PAH features, and derive a calibration between PAH luminosity and star formation rate. Finally, we show that ULIRGs with silicate absorption strengths S_sil of 0.8 ≲ S_sil ≲ 2.4 are likely to be powered mainly by star formation, but that ULIRGs with S_sil ≲ 0.8, and possibly those with S_sil ≳ 2.4, contain an IR-luminous AGN.

We simulate the collapse of isolated dwarf galaxies using SPH + N-body simulations including a physically motivated description of the effects of supernova feedback. As the gas collapses and stars form, the supernova feedback disrupts enough gas to temporarily quench star formation. The gas flows outward into a hot halo, where it cools until star formation can continue once more and the cycle repeats. The star formation histories of isolated Local Group dwarf galaxies exhibit similar episodic bursts of star formation. We examine the mass dependence of the stellar velocity dispersions and find that they are no less than half the velocity of the halos measured at the virial radius.

We present a weak-lensing analysis of 22 early-type (strong) lens galaxies, based on deep HST images obtained as part of the Sloan Lens ACS Survey. Using advanced techniques to control systematic uncertainties, we show that weak-lensing signal is detected out to ~300 h^-1 kpc (at the mean lens redshift z = 0.2). We analyze blank control fields from COSMOS in the same manner, inferring that the residual systematic uncertainty in the tangential shear is less than 0.3%. A joint strong- and weak-lensing analysis shows that the average total mass density profile is consistent with isothermal (i.e., ρ ∝ r^-2) over two decades in radius (3-300 h^-1 kpc, approximately 1-100 effective radii). This finding extends by over an order of magnitude in radius previous results, based on strong lensing and/or stellar dynamics, that luminous and dark components ``conspire'' to form an isothermal mass distribution. In order to disentangle the contributions of luminous and dark matter, we fit a two-component mass model (de Vaucouleurs+NFW) to the weak- and strong-lensing constraints. It provides a good fit to the data with only two free parameters: (1) the average stellar mass-to-light ratio M_*/L_V = 4.48 ± 0.46 hM_☉L (at z = 0.2), in agreement with that expected for an old stellar population; (2) the average virial mass-to-light ratio M_vir/L_V = 246hM_☉L. Taking into account the scatter in the mass-luminosity relation, the latter result is in good agreement with semianalytical models of massive galaxy formation. The dark matter fraction inside the sphere of radius, the effective radius, is found to be 27% ± 4%. Our results are consistent with galaxy-galaxy lensing studies of early-type galaxies that are not strong lenses, in the 30-300 h^-1 kpc radius range. Thus, within the uncertainties, our results are representative of early-type galaxies in general.

Galactic disks in triaxial dark matter halos become deformed by the elliptical potential in the plane of the disk in such a way as to counteract the halo ellipticity. We develop a technique to calculate the equilibrium configuration of such a disk in the combined disk-halo potential, which is based on the method of Jog but accounts for the radial variation in both the halo potential and the disk ellipticity. This crucial ingredient results in qualitatively different behavior of the disk: the disk circularizes the potential at small radii, even for a reasonably low disk mass. This effect has important implications for proposals to reconcile cuspy halo density profiles with low surface brightness galaxy rotation curves using halo triaxiality. The disk ellipticities in our models are consistent with observational estimates based on two-dimensional velocity fields and isophotal axis ratios.

We have identified seven red supergiants (RSGs) in the Large Magellanic Cloud (LMC) and four RSGs in the Small Magellanic Cloud (SMC), all of which have spectral types that are considerably later than the average type observed in their parent galaxy. Using moderate-resolution optical spectrophotometry and the MARCS stellar atmosphere models, we determine their physical properties and place them on the H-R diagram for comparison with the predictions of current stellar evolutionary tracks. The radial velocities of these stars suggest that they are likely all members of the Clouds, rather than foreground dwarfs or halo giants. Their locations in the H-R diagram also show us that these stars are cooler than the current evolutionary tracks allow, appearing to the right of the Hayashi limit, a region in which stars are no longer in hydrostatic equilibrium. These stars exhibit considerable variability in their V magnitudes, and three of these stars also show changes in their effective temperatures (and spectral types), with respective variations of over a magnitude and 3%-4% on the timescales of months. One of these stars, [M2002] SMC 055188, was caught in an M4.5 I state, as late as that seen in HV 11423 at its recent extreme: considerably later, and cooler, than any other supergiant in the SMC. In addition, we find evidence of variable extinction due to circumstellar dust and changes in the stars' luminosities, also consistent with our recent findings for HV 11423—when these stars are hotter, they are also dustier and more luminous. We suggest that these stars have unusual properties because they are in an unstable (and short lived) evolutionary phase.

The Gould Belt (GB) is a system of gas and young, bright stars distributed along a plane that is inclined with respect to the main plane of the Milky Way. Observational evidence suggests that the GB is our closest star formation complex, but its true nature and origin remain rather controversial. In this work we analyze the fractal structure of the stellar component of the GB. In order to do this, we tailor and apply an algorithm that estimates the fractal dimension in a precise and accurate way, avoiding both boundary and small-data set problems. We find that early OB stars (of spectral types earlier than B4) in the GB have a fractal dimension very similar to that of the gas clouds in our Galaxy. On the contrary, stars in the GB of later spectral types show a larger fractal dimension, similar to that found for OB stars of both age groups in the local Galactic disk (LGD). This result seems to indicate that while the younger OB stars in the GB preserve the memory of the spatial structure of the cloud where they were born, older stars are distributed following a similar morphology as that found for the LGD stars. The possible causes for these differences are discussed.

We present Spitzer Space Telescope and Chandra X-Ray Observatory observations of the composite Galactic supernova remnant Kes 75 (G29.7-0.3). We use the detected flux at 24 μm and hot gas parameters from fitting spectra from new, deep X-ray observations to constrain models of dust emission, obtaining a dust-to-gas mass ratio M_dust/M_gas ~ 10^-3. We find that a two-component thermal model, nominally representing shocked swept-up interstellar or circumstellar material and reverse-shocked ejecta, adequately fits the X-ray spectrum, albeit with somewhat high implied densities for both components. We surmise that this model implies a Wolf-Rayet progenitor for the remnant. We also present infrared flux upper limits for the central pulsar wind nebula.

Mass loss from massive stars leads to the formation of circumstellar wind-blown bubbles surrounding the star, bordered by a dense shell. When the star ends its life in a supernova (SN) explosion, the resulting shock wave expands within this modified medium. Following up on an introductory paper (Dwarkadas), herein we study the evolution of a SN in the bubble formed by a 35 M_☉ star that evolves through the phases O star, red supergiant, and Wolf-Rayet star. We model the evolution of the circumstellar medium, and the expansion of the SN shock wave within this medium. Our multidimensional simulations clearly reveal density and pressure fluctuations within the surrounding medium, the presence of hydrodynamic instabilities, the growth of vorticity, and the onset of turbulence. The SN shock interaction with this medium, and then with the dense shell, gives rise to transmitted and reflected shocks. Their effect on the X-ray emission is examined. In this particular case the shock wave is trapped in the dense shell for several doubling times. The turbulent interior, coupled with the density and pressure fluctuations, lead to a corrugated SN shock that impacts the dense shell. The impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before others. As each interaction is accompanied by an increase in the X-ray and optical emission, different parts of the shell will "light up" at different times. The situation is resemblant of the scenario in SN 1987A. The reflected shock formed upon shell impact comprises several smaller shocks with different velocities, which are not necessarily moving radially inward. The spherical symmetry of the initial shock wave is completely destroyed.

We present new λ = 6 cm radio observations (Stokes I, Q, and U and hydrogen recombination line) of the Galactic object G84.9+0.5, previously classified as a supernova remnant. Radio recombination line (RRL) emission near 6 cm is detected in deep GBT observations, and we are able to separate the 7.6 mK line detected from this object (appearing at v_LSR = -40 km s^-1) from the line emitted by ionized gas of W80 in the foreground (T_l = 5.4 mK; v_LSR ~ 0 km s^-1) along the same line of sight (LOS). Detection of RRL emission from G84.9+0.5 and the absence of polarized emission at 6 cm imply that this object is an H II region. Rather than a Gaussian, a Voigt function better describes the extended line profile of G84.9+0.5, which has a low-level "wing" extending into its negative-velocity end. A Monte Carlo analysis of noisy synthetic spectra is presented, and it is concluded the wing is not spurious. Two physical explanations for the wing (pressure broadening and an outflow of gas) are considered. We favor that of a champagne-type outflow in the gas flowing along the inside wall of a known molecular cloud in the vicinity of the nebula (at -40 km s^-1), making G84.9+0.5 a "blister" type H II region viewed face-on. We find T_e = 9900 K and n_e = 20 cm^-3 from a non-LTE analysis of the peak toward the RRL, and a total H II mass of 440 M_☉. A distance of 4.9 kpc is determined for this object. An IR analysis using MSX and 2MASS data is presented, showing H II region colors for G84.9+0.5 and identifying a possible exciting star for this H II region.

The Sh 2-158 gas complex kinematics is analyzed using four lines from three different ions (Hα, [O III] λ5007, and [S II] λλ6727, 6731) and the CO 1-0 line. The O⁺⁺ and S⁺ data cubes were obtained using MOS FP at the CFHT, while the H⁺ data cube was obtained using FaNTOmM at the Observatoire du mont Mégantic. More than 200,000 spectra (S/N ≥ 5) were obtained. Maps of the radial velocity fields, the velocity line width field, and the electronic density field are discussed. All ionic mean radial velocities are blueshifted with respect to the molecular cloud (V_LSR = -55.16 ± 0.02 km s^-1), more so as one goes from [S II] to Hα to [O III]. Two flows originating from the molecular cloud are identified. The encounter of the two flows, and possibly stellar winds, induces turbulence near the stars, causing larger line widths (≈10 km s^-1) than elsewhere in the field. The mean [S II] line width is smaller than the mean [O III] line width, which is smaller than the mean Hα line width. Those differences between the ions are explained by the smaller [O III] Strömgren sphere compared to the Hα Strömgren sphere and the restriction of [S II] to a shell of gas near the molecular cloud. The most probable density value is 225 ± 25 cm^-3. The observations are mostly in agreement with the Champagne model. A geometrical model is proposed for Sh 2-158.

We present calculations of the continuum ultraviolet radiation field (91.2 nm < λ < 550 nm) penetrating both uniform and clumpy (3D turbulent supersonic magnetohydrodynamic) starless molecular gas layers. We find that despite the self-shielding of clumps, pristine (i.e., unreddened) radiation penetrates deeply both the cloud's volume and its mass, resulting in a brighter and bluer intracloud radiation field compared to that in an equivalent uniform cloud. Motivated by these results, we construct and test a toy model ray-tracing scheme for the radiative transfer that fits the UV-visible spectral range with a three-parameter function. We calculate the photoionization rates, Γ, of the elements C, Na, Mg, Si, S, and Fe as functions of the visual extinction A_V along lines of sight. Typically, the difference in Γ(A_V) between the clumpy and uniform clouds increases to orders of magnitude at even modest extinctions (A_V ~ 2). Photoionization in the clumpy model extends 2-3 times deeper than in the uniform case, and it dominates cosmic-ray ionization throughout almost the entire volume. We encapsulate these average results in a parameterized form appropriate for when an approximate treatment of the effects of clumpiness is desired. However, the large point-to-point variance in this behavior suggests that uncertainties may arise when using mean values to model particular lines of sight in detail. Ideally, these new results would be used in conjunction with established results for homogeneous clouds in order to span a range of behavior that arises due to cloud inhomogeneities. We briefly explore the importance of the adopted dust properties, characterized by the selective extinction R_V and the scattering parameter g. We find that the UV field is considerably less sensitive to these dust properties in clumpy clouds, emphasizing the preeminence of geometry.

We present maps of 7.78 deg² of the Lupus molecular cloud complex at 24, 70, and 160 μm. They were made with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the Spitzer Legacy Program "From Molecular Cores to Planet-Forming Disks" (c2d). The maps cover three separate regions in Lupus, denoted I, III, and IV. We discuss the c2d pipeline and how our data processing differs from it. We compare source counts in the three regions with two other data sets and predicted star counts from the Wainscoat model. This comparison shows the contribution from background galaxies in Lupus I. We also create two color-magnitude diagrams using the 2MASS and MIPS data. From these results, we can identify background galaxies and distinguish them from probable young stellar objects. The sources in our catalogs are classified based on their spectral energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample of young stellar object candidates. From 2MASS data, we create extinction maps for each region and note a strong correspondence between the extinction and the 160 μm emission. The masses we derived in each Lupus cloud from our extinction maps are compared to masses estimated from ¹³CO and C¹⁸ O and found to be similar to our extinction masses in some regions, but significantly different in others. Finally, based on our color-magnitude diagrams, we selected 12 of our reddest candidate young stellar objects for individual discussion. Five of the 12 appear to be newly discovered YSOs.

We report the first detection of 3 μm water ice absorption in a protoplanetary disk. Low-resolution spectroscopy with Subaru IRCS was carried out for two T Tauri stars with an edge-on disk, HK Tau B and HV Tau C. A 3 μm deep water ice absorption (τ ≥ 1) toward both objects was detected. Contribution by foreground cloud material to the ice absorption should be small, since A_V ≤ 3 toward HK Tau A and HV Tau A, HV Tau B. Although HV Tau C is reported to have a small amount of envelope material, its mass is insufficient to produce the large optical depth of the detected water ice. In addition, HK Tau B does not have any significant envelope mass. Therefore, the water ice exists inside the disks of these objects. The optical depth profile of the water ice absorption in the protoplanetary disks does not show any significant difference from those of protostellar sources. The water ice optical depth for HV Tau C showed a large variation (Δτ = 0.59) in two observing epochs separated by 2.32 yr. Assuming the ice absorption comes from a spherical cloud at 100 AU and Keplerian rotation, it suggests that a Pluto mass gas and dust cloud with a size of 1.4 AU may have passed by the line of sight. The lack of variability of the continuum level of HV Tau C at the two epochs implies that the dust grains with an icy mantle are segregated from the grains without an icy mantle.

One of the central goals of the Spitzer Legacy Project ``From Cores to Disks'' (c2d) is to determine the frequency of circumstellar disks around weak-line T Tauri stars (WTTSs) and to study the properties and evolutionary status of these disks. Here we present a census of disks for a sample of over 230 WTTSs located in the c2d IRAC and MIPS maps of the Ophiuchus, Lupus, and Perseus Molecular Clouds. We find that ~20% of the WTTSs in a magnitude-limited subsample have IR excesses at IRAC wavelengths. These disks frequencies are ~3-6 times larger than that recently found for a sample of relatively isolated WTTSs located outside the highest extinction regions covered by the c2d maps. The disk fractions we find are more consistent with those obtained in recent Spitzer studies of WTTSs in young clusters such as IC 348 and Tr 37. According to their location in the H-R diagram, the WTTSs with excesses in our sample are among the younger part of the age distribution. Still, up to ~50% of the apparently youngest stars in the sample show no evidence of IR excess, suggesting that the circumstellar disks of a sizable fraction of pre-main-sequence stars dissipate in a timescale of ~1 Myr. We also find that none of the stars in our sample apparently older than ~10 Myr have detectable circumstellar disks at wavelengths <24 μm. The WTTS disks in our sample exhibit a wide range of properties (SED morphology, inner radius, L_disk/L_*, etc.) that bridge the gaps observed between the CTTSs and the debris disk regimes.

Observations by the Cores to Disk Legacy Team with the Spitzer Space Telescope have identified a low-luminosity, mid-infrared source within the dense core, Lynds 1014, which was previously thought to harbor no internal source. Follow-up near-infrared and submillimeter interferometric observations have confirmed the protostellar nature of this source by detecting scattered light from an outflow cavity and a weak molecular outflow. In this paper, we report the detection of centimeter continuum emission with the VLA. The emission is characterized by a quiescent, unresolved 90 μJy 6 cm source within 0.2'' of the Spitzer source. The spectral index of the quiescent component is α = 0.37 ± 0.34 between 6 and 3.6 cm. A factor of 2 increase in 6 cm emission was detected during one epoch and circular polarization was marginally detected at the 5 σ level with Stokes V/I = 48% ± 16%. We have searched for 22 GHz H₂O maser emission toward L1014-IRS, but no masers were detected during seven epochs of observations between 2004 June and 2006 December. L1014-IRS appears to be a low-mass, accreting protostar, which exhibits centimeter emission from a thermal jet or a wind, with a variable nonthermal emission component. The quiescent cm radio emission is noticeably above the correlation of 3.6 and 6 cm luminosity versus bolometric luminosity, indicating more radio emission than expected. In this paper, we characterize the centimeter continuum emission in terms of observations of other low-mass protostars, including updated correlations of centimeter continuum emission with bolometric luminosity and outflow force, and discuss the implications of recent larger distance estimates on the physical attributes of the protostar and dense molecular core.

We propose a new model within the "quark nova" scenario to interpret the recent observations of early afterglows of long gamma-ray bursts (GRBs) with the Swift satellite. This is a three-stage model within the context of a core-collapse supernova. Stage 1 is an accreting (proto-)neutron star leading to a possible delay between the core collapse and the GRB. Stage 2 is an accreting quark star, generating the prompt GRB. Stage 3, which occurs only if the quark star collapses to form a black hole, consists of an accreting black hole. The jet launched in this accretion process interacts with the ejecta from stage 2, and could generate the flaring activity frequently seen in X-ray afterglows. This model may be able to account for both the energies and the timescales of GRBs, in addition to the newly discovered early X-ray afterglow features.

We show that the prompt and afterglow X-ray emission of GRB 060218, as well as its early (t ≲ 1 day) optical-UV emission, can be explained by a model in which a radiation-mediated shock propagates outward from a compact progenitor star into a dense wind. The prompt thermal X-ray emission is produced in this model when the mildly relativistic shock, β ≈ 0.85, carrying a few times 10⁴⁹ erg, reaches the wind (Thomson) photosphere, where the postshock thermal radiation is released and the shock becomes collisionless. Adopting this interpretation of the thermal X-ray emission, we predict a subsequent X-ray afterglow, due to synchrotron emission and inverse Compton scattering of supernova UV photons by electrons accelerated in the collisionless shock. Early optical-UV emission is also predicted, due to the cooling of the outer δM ~ 10^-3M_☉ envelope of the star, which was heated to high temperature during the shock passage. The observed X-ray afterglow and the early optical-UV emission are both consistent with those expected in this model. Detailed analysis of the early optical-UV emission may provide detailed constraints on the density distribution near the stellar surface.

During its first data cycle, between 2005 and the beginning of 2006, the fast repositioning system of the MAGIC telescope allowed the observation of nine different gamma-ray bursts as possible sources of very high energy γ-rays. These observations were triggered by alerts from Swift, HETE-2, and INTEGRAL; they started as quickly as possible after the alerts and lasted for several minutes, with an energy threshold varying between 80 and 200 GeV, depending on the zenith angle of the burst. No evidence for gamma signals was found, and upper limits for the flux were derived for all events using the standard analysis chain of MAGIC. For the bursts with measured redshifts, the upper limits are compatible with a power-law extrapolation, when the intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the metagalactic radiation field.

We prescribe a pseudo-Newtonian vector potential for studying accretion disks around Kerr black holes. The potential is useful for studying the inner properties of a disk not confined to the equatorial plane where general relativistic effects are indispensable. Therefore, we incorporate the essential properties of the metric at the inner radii through the pseudo-Newtonian potential derived from the general Kerr spacetime. The potential, reproducing most of the salient features of general relativity, is valid for the entire regime of the Kerr parameter. It reproduces the last stable circular orbit exactly as that in the Kerr geometry. It also reproduces the last bound orbit and energy at the last stable circular orbit with a maximum error ~7% and ~15%, respectively, up to an orbital inclination 30°.

We present the results of numerical experiments, in which we have investigated the influence of the inelastic neutrino-helium interactions on the standing accretion shock instability supposed to occur in the postbounce supernova core. The axisymmetric hydrodynamical simulations of accretion flows through the standing accretion shock wave onto the proto-neutron star show that the interactions are relatively minor and the linear growth of the shock instability is hardly affected. The extra heating given by the inelastic reactions becomes important for the shock revival after the instability enters the nonlinear regime, but only when the neutrino luminosity is very close to the critical value at which the shock would be revived without the interactions. We have also studied the dependence of the results on the initial amplitudes of perturbation and the temperatures of mu and tau neutrinos.

We study black hole formation and the neutrino signal from the gravitational collapse of a nonrotating massive star of 40 M_☉. Adopting two different sets of realistic equations of state (EOSs) for dense matter, we perform numerical simulations of general relativistic ν-radiation hydrodynamics under spherical symmetry. We make comparisons of core bounce, shock propagation, evolution of nascent proto-neutron stars, and the resulting recollapse to a black hole to reveal the influence of EOSs. We also explore the influence of EOSs on neutrino emission during the evolution toward black hole formation. We find that the speed of contraction of the nascent proto-neutron star, whose mass increases quickly due to the intense accretion, is different depending on the EOS and that the resulting profiles of density and temperature differ significantly. The black hole formation occurs at 0.6-1.3 s after bounce, when the proto-neutron star exceeds its maximum mass, which is crucially determined by the EOS. We find that the average energies of neutrinos increase after bounce because of rapid temperature increase, but at different speeds depending on the EOS. The duration of neutrino emission up to black hole formation is found to be different according to different recollapse timing. These characteristics of neutrino signatures are distinguishable from those for ordinary proto-neutron stars in successful core-collapse supernovae. We discuss the idea that a future detection of neutrinos from a black hole-forming collapse will contribute to revealing the black hole formation and to constraining the EOS at high density and temperature.

The nature of ultraluminous X-ray sources (ULXs) in nearby galaxies is one of the major open questions in modern X-ray astrophysics. One possible explanation for these objects is an inhomogeneous, radiation-dominated accretion disk around a ~10 M_☉ black hole, the so-called photon bubble model. While previous studies of this model have focused primarily on its radiation hydrodynamics aspects, in this paper, we provide an analysis of its X-ray spectral (continuum and possible edge and line) characteristics. Compton reflection between high- and low-density regions in the disk may provide the key to distinguishing this model from others, such as accretion onto an intermediate-mass black hole. We couple a Monte Carlo-Fokker-Planck radiation transport code with the XSTAR code for reflection to simulate the photon spectra produced in a photon bubble model for ULXs. We find that reflection components tend to be very weak and in most cases not observable, and we make predictions for the shape of the high-energy Comptonizing spectra. In many cases, the Comptonization dominates the spectra even down to approximately a few keV. In one simulation, a ~9 keV feature was found, which may be considered a signature of photon bubbles in ULXs; furthermore, we make predictions of high-energy power laws which may be observed by future instruments.

Correlations between the quasi-periodic oscillations (QPOs) and the spectral power-law index have been reported for a number of black hole candidate sources and for four neutron star (NS) sources, 4U 0614+09, 4U 1608-52, 4U 1728-34, and Sco X-1. An examination of QPO frequencies and index relationship in Cyg X-2 is reported herein. The RXTE spectrum of Cyg X-2 can be adequately represented by a simple two-component model of Compton upscattering with a soft photon electron temperature of about 0.7 keV and an iron K line. Inferred spectral power-law index shows correlation with the low QPO frequencies. We find that the Thomson optical depth of the Compton cloud (CC) τ, in framework of spherical geometry, is in the range of ~4-6, which is consistent with the surface of the neutron star (NS) being obscured. The NS high-frequency pulsations are presumably suppressed as a result of photon scattering off CC electrons because of such high values of τ. We also point out a number of similarities in terms of timing (presence of low- and high-frequency QPOs) and spectral (high CC optical depth and low CC plasma temperature) appearances between Cyg X-2 and Sco X-1.

We analyze a large collection of RXTE archive data from 1997 April to 2003 August of the bright X-ray source Scorpius X-1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by studying energy spectra from selected regions in the Z track of its color-color diagram (CD). A two-component model, consisting of a soft thermal component interpreted as thermal emission from an accretion disk and a thermal Comptonization component, is unable to fit the whole 3-200 keV energy spectrum at low accretion rates. Strong residuals in the highest energy band of the spectrum require the addition of a third component that can be fitted with a power-law component, which could represent a second thermal Comptonization from a much hotter plasma, or a hybrid thermal/nonthermal Comptonization. The presence of this hard emission in Sco X-1 has been previously reported, however, without a clear relation with the accretion rate. We show, for the first time, that there exists a common trend in the spectral evolution of the source, where the spectral parameters change in correlation with the position of the source in the CD. In particular, using a hybrid Comptonization model, we show that the power supplied to the nonthermal distribution can be as high as half of the total hard power injected in heating the electron distribution. We discuss the physical implications derived from the results of our analysis, with a particular emphasis on the hardest part of the X-ray emission and its possible origins.

We present XMM-Newton observations of the black hole X-ray nova V404 Cyg in quiescence. Its quiescent spectrum can be best fitted by a simple power law with slope Γ ~ 2. The spectra are consistent with that expected for the advection-dominated accretion flow (ADAF). V404 Cyg was roughly equal in luminosity compared to the previous observation of Chandra. We see variability of a factor of 4 during the observation. We find no evidence for the presence of fluorescent or H-like/He-like iron emission, with upper limits of 52 and 110 eV, respectively. The limit on the fluorescent emission is improved by a factor of 15 over the previous estimate, and the restriction on H-like/He-like emission is lower than predicted from models by a factor of roughly 2.

We report the discovery of two new accreting pulsating white dwarf stars among the cataclysmic variables of the Sloan Digital Sky Survey: SDSS J074531.91+453829.5 and SDSS J091945.10+085710.0. We observe high-amplitude nonsinusoidal variations of 4.5%-7% at a period close to 1230 s in the optical light curves of SDSS J074531.91+453829.5 and a low-amplitude variation of 0.7%-1.6% near 260 s in the light curves of SDSS J091945.10+085710.0. We infer that these optical variations are a consequence of nonradial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. However, we cannot rule out the remote possibility that the 260 s period could be the spin period of the accreting white dwarf SDSS J091945.10+085710.0. We also uncovered a nonvariable, SDSS J171145.08+301320.0, during our search; our two observing runs exclude any pulsation-related periodicities in the range 85-1400 s with an amplitude ≥0.5%. This discovery paper brings the total number of known accreting white dwarf pulsators to 11.

We present phase-resolved spectroscopy of the short-period cataclysmic variable WZ Sge obtained with the Hubble Space Telescope. We were able to resolve the orbital motion of a number of absorption lines that likely probe the environment near the accreting white dwarf. The radial velocities derived from simultaneous fits to 13 absorption lines indicate an orbital velocity semi-amplitude of K_UV = km s^-1. However, we find that the phase zero is offset from the white dwarf ephemeris by +0.1. Our offset and velocity amplitude are very similar to constraints derived from optical emission lines from the quiescent accretion disk, despite the fact that we are probing material much closer to the primary. If we associate the UV amplitude with K₁, our dynamical constraints together with the published K₂ estimates and the known binary inclination of i = 77 ± 2 imply 0.88 M_☉ < M₁ < 1.53 M_☉, 0.078 M_☉ < M₂ < 0.13 M_☉, and 0.075 < q = M₂/M₁ < 0.101. If we interpret the mean velocity of the UV lines [- km s^-1] as being due to the gravitational redshift caused in the high-g environment near the white dwarf, we find v_grav = km s^-1, which provides an independent estimate on the mass of the primary of M₁ = M_☉ when coupled with a mass-radius relation. Our primary mass estimates are in excellent agreement and are also self-consistent with spectrophotometric fits to the UV fluxes despite the observed phase offset. It is at this point unclear what causes the observed phase offset in the UV spectra and by how much it distorts the radial velocity signature from the underlying white dwarf.

We describe the results of 3D numerical simulations of oxygen shell burning and hydrogen core burning in a 23 M_☉ stellar model. A detailed comparison is made to stellar mixing-length theory (MLT) for the shell-burning model. Simulations in 2D are significantly different from 3D, in terms of both flow morphology and velocity amplitude. Convective mixing regions are better predicted using a dynamic boundary condition based on the bulk Richardson number than by purely local, static criteria like Schwarzschild or Ledoux. MLT gives a good description of the velocity scale and temperature gradient for shell convection; however, there are other important effects that it does not capture, mostly related to the dynamical motion of the boundaries between convective and nonconvective regions. There is asymmetry between upflows and downflows, so the net kinetic energy flux is not zero. The motion of convective boundaries is a source of gravity waves; this is a necessary consequence of the deceleration of convective plumes. Convective "overshooting" is best described as an elastic response by the convective boundary, rather than ballistic penetration of the stable layers by turbulent eddies. The convective boundaries are rife with internal and interfacial wave motions, and a variety of instabilities arise that induce mixing through a process best described as turbulent entrainment. We find that the rate at which material entrainment proceeds at the boundaries is consistent with analogous laboratory experiments and simulation and observation of terrestrial atmospheric mixing. In particular, the normalized entrainment rate E = u_E/σ_H is well described by a power-law dependence on the bulk Richardson number Ri_B = ΔbL/σ for the conditions studied, 20 ≲ Ri_B ≲ 420. We find E = ARi, with best-fit values log A = 0.027 ± 0.38 and n = 1.05 ± 0.21. We discuss the applicability of these results to stellar evolution calculations.

Iron and neighboring nuclei are formed in massive stars shortly before core collapse and during their supernova outbursts, as well as during thermonuclear supernovae. Complete and incomplete silicon burning are responsible for the production of a wide range of nuclei with atomic mass numbers from 28 to 64. Because of the large number of nuclei involved, accurate modeling of silicon burning is computationally expensive. However, examination of the physics of silicon burning has revealed that the nuclear evolution is dominated by large groups of nuclei in mutual equilibrium. We present a new hybrid equilibrium-network scheme which takes advantage of this quasi-equilibrium in order to reduce the number of independent variables calculated. This allows accurate prediction of the nuclear abundance evolution, deleptonization, and energy generation at a greatly reduced computational cost when compared to a conventional nuclear reaction network. During silicon burning, the resultant QSE-reduced network is approximately an order of magnitude faster than the full network it replaces and requires the tracking of less than a third as many abundance variables, without significant loss of accuracy. These reductions in computational cost and the number of species evolved make QSE-reduced networks well suited for inclusion within hydrodynamic simulations, particularly in multidimensional applications.

The concomitant overabundances of C, N, and s-process elements are commonly ascribed to the complex interplay of nucleosynthesis, mixing, and mass loss taking place in asymptotic giant branch (AGB) stars. At low metallicity, the enhancement of C and/or N can be up to 1000 times larger than the original iron content and significantly affects the stellar structure and its evolution. For this reason, the interpretation of the already available and still growing amount of data concerning C-rich metal-poor stars belonging to our Galaxy as well as to dwarf spheroidal galaxies would require reliable AGB stellar models for low and very low metallicities. In this paper we address the question of calculation and use of appropriate opacity coefficients, which take into account the C enhancement caused by the third dredge-up. A possible N enhancement, caused by the cool bottom process or by the engulfment of protons into the convective zone generated by a thermal pulse and the subsequent huge third dredge-up, is also considered. Based on up-to-date stellar models, we illustrate the changes induced by the use of these opacity coefficients on the physical and chemical properties expected for these stars.

The B[e] phenomenon is defined as the simultaneous presence of low-excitation forbidden line emission and strong infrared excess in the spectra of early-type stars. It was discovered in our Galaxy 30 years ago in the course of the early exploration of the infrared sky and initially identified in 65 Galactic objects, of which nearly half remained unclassified. The phenomenon is associated with objects at different evolutionary stages, ranging from the pre-main-sequence to the planetary nebula stage. We review the studies of both the original 65 and subsequently identified Galactic stars with the B[e] phenomenon. A new classification is proposed for stars with the B[e] phenomenon based on the time of dust formation in their environments. Properties of the unclassified Galactic B[e] stars are analyzed. We propose that these objects are binary systems that are currently undergoing or have recently undergone a phase of rapid mass exchange, associated with a strong mass loss and dust formation. A new name, FS CMa stars, and classification criteria are proposed for the unclassified B[e] stars.

The massive interacting binary RY Scuti is an important representative of an active mass-transferring system that is changing before our eyes and which may be an example of the formation of a Wolf-Rayet star through tidal stripping. Utilizing new and previously published spectra, we present examples of how a number of illustrative absorption and emission features vary during the binary orbit. We identify spectral features associated with each component, calculate a new, double-lined spectroscopic binary orbit, and find masses of 7.1 ± 1.2 M_☉ for the bright supergiant and 30.0 ± 2.1 M_☉ for the hidden massive companion. Through tomographic reconstruction of the component spectra from the composite spectra, we confirm the O9.7 Ibpe spectral class of the bright supergiant and discover a B0.5 I spectrum associated with the hidden massive companion; however, we suggest that the latter is actually the spectrum of the photosphere of the accretion torus immediately surrounding the massive companion. We describe the complex nature of the mass-loss flows from the system in the context of recent hydrodynamical models for β Lyr, leading us to conclude RY Scuti has matter leaving the system in two ways: (1) a bipolar outflow from winds generated by the hidden massive companion, and (2) an outflow from the bright O9.7 Ibpe supergiant in the region near the L2 point to fill out a large, dense circumbinary disk. This circumbinary disk (radius ≈1 AU) may feed the surrounding double-toroidal nebula (radius ≈2000 AU).

The results of the Königstuhl survey in the Southern Hemisphere are presented. I have searched for common proper motion companions to 173 field very low mass stars and brown dwarfs with spectral types >M5.0 V and magnitudes J ≲ 14.5 mag. I have measured for the first time the common proper motion of two new wide systems containing very low mass components, Königstuhl 2 AB and 3 A-BC. Together with Königstuhl 1 AB and 2M 0126-50 AB, they are among the widest systems in their respective classes (r = 450-11,900 AU). I have determined the minimum frequency of field wide multiples (r > 100 AU) with late-type components at 5.0% ± 1.8% and the frequency of field wide late-type binaries with mass ratios q > 0.5 at 1.2% ± 0.9%. These values represent a key diagnostic of evolution history and low-mass star and brown dwarf formation scenarios. In addition, the proper motions of 62 field very low mass dwarfs are measured here for the first time.

We report the mid- and far-infrared properties of nearby M dwarfs. Spitzer MIPS measurements were obtained for a sample of 62 stars at 24 μm, with subsamples of 41 and 20 stars observed at 70 and 160 μm, respectively. We compare the results with current models of M star photospheres and look for indications of circumstellar dust in the form of significant deviations of K-[24 μm] colors and 70 μm/24 μm flux ratios from the average M star values. At 24 μm, all 62 of the targets were detected; 70 μm detections were achieved for 20 targets in the subsample observed, and no detections were seen in the 160 μm subsample. No clear far-infrared excesses were detected in our sample. The average far-infrared excess relative to the photospheric emission of the M stars is at least 4 times smaller than the similar average for a sample of solar-type stars. However, this limit allows the average fractional infrared luminosity in the M-star sample to be similar to that for more massive stars. We have also set low limits (10^-4 to 10^-9M_⊕ depending on location) for the maximum mass of dust possible around our stars.

We use newly observed and published near-infrared spectra, together with synthetic spectra obtained from model atmospheres, to derive physical properties of three of the latest type T dwarfs. A new R ≈ 1700 spectrum of the T7.5 dwarf HD 3651B, together with existing data, allows a detailed comparison to the well-studied and very similar dwarf Gl 570D. We find that HD 3651B has both higher gravity and higher metallicity than Gl 570D, with best-fit atmospheric parameters of T_eff = 820-830 K, log g = 5.4-5.5, [m/H] = +0.2, and K_zz = 10⁴ cm² s^-1. Its age is 8-12 Gyr, and its implied mass is 60-70 M_J. We perform a similar analysis of the T8 and T7.5 dwarfs 2MASS J09393548-2448279 and 2MASS J11145133-2618235 using published data, comparing them to the well-studied T8, 2MASS J04151954-0935066. We find that these two dwarfs have effectively the same T_eff as the reference dwarf, and similar or slightly higher gravities, but lower metallicities. The derived parameters are T_eff = 725-775 K and [m/H] = -0.3; log g = 5.3 - 5.45 for 2MASS J09393548-2448279 and log g = 5.0 - 5.3 for 2MASS J11145133-261823. The age and mass are ~10 Gyr and 60 M_J for 2MASS J09393548-2448279, and ~5 Gyr and 40 M_J for 2MASS J11145133-261823. A serious limitation to such analyses is the incompleteness of the line lists for transitions of CH₄ and NH₃ at λ ≤ 1.7 μm, which are also needed for synthesizing the spectrum of the later, cooler, Y type. Spectra of Saturn and Jupiter, and of laboratory CH₄ and NH₃ gas, suggest that NH₃ features in the Y and J bands may be useful as indicators of the next spectral type, and not features in the H and K bands, as previously thought. However, until cooler objects are found, or the line lists improve, large uncertainties remain, as the abundance of NH₃ is likely to be significantly below the chemical equilibrium value. Moreover, inclusion of laboratory NH₃ opacities in our models predicts band shapes that are discrepant with existing data. It is possible that the T spectral class will have to be extended to temperatures around 400 K, when water clouds condense in the atmosphere and dramatically change the spectral energy distribution of the brown dwarf.

We report 35 radial velocity measurements of HD 149026 taken with the Keck Telescope. Of these measurements, 15 were made during the transit of the companion planet HD 149026b, which occurred on 2005 June 25. These velocities provide a high-cadence observation of the Rossiter-McLaughlin effect, the shifting of photospheric line profiles that occurs when a planet occults a portion of the rotating stellar surface. We combine these radial velocities with previously published radial velocity and photometric data sets and derive a composite best-fit model for the star-planet system. This model confirms and improves previously published orbital parameters, including the remarkably small planetary radius, the planetary mass, and the orbital inclination, found to be R_p/R_Jup = 0.718 ± 0.065, M_p/M_Jup = 0.352 ± 0.025, and I = 86.1° ± 1.4°, respectively. Together the planetary mass and radius determinations imply a mean planetary density of 1.18 g cm^-3. The new data also allow for the determination of the angle between the apparent stellar equator and the orbital plane, which we constrain to be λ = -12° ± 15°.

We construct an analytic model for the gas accretion rate onto planets embedded in protoplanetary disks as a function of planetary mass, viscosity, scale height, and unperturbed surface density, and systematically study the long-term accretion and final masses of gas giant planets. We first derive an analytical formula for the surface density profile near the planetary orbit from considerations of the balance of force and dynamical stability. Using it in the empirical formula of normalized gas accretion rate that is derived based on hydrodynamic simulations, we then simulate the mass evolution of gas giant planets in viscously evolving disks. We finally determine the final mass as a function of semimajor axis of the planet. We find that the disk can be divided into three regions characterized by different processes by which the final mass is determined. In the inner region, the planet grows quickly and forms a deep gap to suppress the growth by itself before disk dissipation. The final mass shows the same trend as the mass determined by the viscous condition for gap opening, but is about 10 times larger than that. In the intermediate region, the disk's viscous diffusion limits gas accretion onto planets before deep gap formation. The final mass can be up to the disk mass, when the disk's viscous evolution occurs faster than disk evaporation. In the outer region, planets capture only tiny amounts of gas within the disk lifetime to form Neptune-like planets. We also derive analytic formulae for the final masses in the different regions and the locations of the boundaries, which are helpful to gain a systematic understanding of the masses of gas giant planets.

We measure the relation between divergence and vorticity of subsurface horizontal flows as a function of unsigned surface magnetic flux. Observations from the Michelson Doppler Imager (MDI) Dynamics Program and Global Oscillation Network Group (GONG) have been analyzed with a standard ring-diagram technique to measure subsurface horizontal flows from the surface to a depth of about 16 Mm. We study residual horizontal flows after subtracting large-scale trends (low-order polynomial fits in latitude) from the measured velocities. On average, quiet regions are characterized by weakly divergent horizontal flows and small anticyclonic vorticity (clockwise in the northern hemisphere), while locations of high activity show convergent horizontal flows combined with cyclonic vorticity (counterclockwise in the northern hemisphere). Divergence and vorticity of horizontal flows are anticorrelated (correlated) in the northern (southern) hemisphere. This is especially noticeable at greater depth, where the relation between divergence and vorticity of horizontal flows is nearly linear. These trends show a slight reversal at the highest levels of magnetic flux; the vorticity amplitude decreases at the highest flux levels, while the divergence changes sign at depths greater than about 10 Mm. The product of divergence and vorticity of the horizontal flows, a proxy of the vertical contribution to the kinetic helicity density, is on average negative (positive) in the northern (southern) hemisphere. The helicity proxy values are greater at locations of high magnetic activity than at quiet locations.

Different life spans of sunspots suggest their origin at different depths, and by measuring magnetic fluxes from their first observation on the surface, one can estimate the strength of magnetic flux at different anchoring depths. From SOHO MDI magnetograms, we infer the strength of magnetic flux and rate of emergence of magnetic flux at different anchoring depths in the solar convective envelope by measuring initial magnetic fluxes of the well-developed sunspots on the surface. Important findings are: (1) the majority of the spot groups that have first observation on the surface are bipolar; (2) irrespective of their sizes, the bipolar spots with different life spans have average magnetic field strengths of ~500 G during their first observation; (3) the average field strength at the site of anchoring depths of the sunspots is estimated to be ~10⁶ G near the base of the convective envelope and ~10⁴ G near the surface; (4) the dynamo—a source of sunspot activity—is distributed throughout the convective envelope; and (5) the rate of emergence of initial magnetic flux of such a distributed dynamo near the base of the convection zone is ~6 × 10¹⁹ Mx day^-1 and is 40% higher than the rate of emergence of initial magnetic flux near the surface.

The highly suppressed thermal transport across the magnetic field in the solar corona makes the determination of the cross-field thermal distribution within coronal loops a powerful diagnostic of the properties of the heating process itself. The cross-field thermal structure is currently being strongly debated. Spectroscopic observations with high temperature fidelity but low spatial resolution indicate that some observed loops are multithermal, whereas imaging observations with high spatial resolution but low temperature fidelity indicate more isothermal conditions. We report here on triple filter observations of coronal loops made by the Transition Region and Coronal Explorer (TRACE), which has the best spatial resolution currently available. We tested the isothermal hypothesis using the emission measure loci technique and found that the loops are consistent with an isothermal plasma near 1.5 MK only if a generous estimate of the photometric uncertainties is used. A more restrictive estimate based on discussions with the TRACE experimenters rules out the isothermal hypothesis. The observations are much better explained by a multithermal plasma with significant emission measure throughout the range 1-3 MK. The details of the emission measure distribution are not well defined, however. Future subarcsecond spectroscopic observations covering a wide range of temperatures are the most promising means of unlocking the thermal structure of the corona.

We describe a new modeling approach to develop a more quantitative understanding of the charge state distributions of the ions of various elements detected in situ during halo coronal mass ejection (CME) events by the Advanced Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution based on observations of CMEs propagating in the plane of the sky and on theoretical models, we integrate time-dependent equations for the ionization balance of various elements to compare with ACE data. We find that plasma in the CME "core" typically requires further heating following filament eruption, with thermal energy input similar to the kinetic energy input. This extra heating is presumably the result of posteruptive reconnection. Plasma corresponding to the CME "cavity" is usually not further ionized, since whether heated or not, the low density gives freeze-in close the Sun. The current analysis is limited by ambiguities in the underlying model CME evolution. Such methods are likely to reach their full potential when applied to data to be acquired by STEREO when at optimum separation. CME evolution observed with one spacecraft may be used to interpret CME charge states detected by the other.

Two coronal mass ejections (CMEs) are presented which were tracked through the LASCO field of view (FOV) within 30 R_☉ and later as interplanetary CMEs (ICMEs) through the SMEI FOV from 80 to 150 R_☉. They were also associated with erupting filaments observed by EIT, providing information on trajectory of propagation. This allowed three-dimensional reconstructions of CME/ICME geometry, along with corrected (not sky plane projected) measurements of distance-time (DT) plots for each event to ~0.5 AU. An investigation of morphology was conducted. The results suggest that fine structures of the CMEs are eroded by the solar wind, and curvature becomes more sharply convex outward, suggesting that ICME footpoints remain fixed to the Sun even at 0.5 AU. We also present two models describing the evolution of CMEs/ICMEs at large distances from the Sun (far from the launch mechanism and effects of gravity and solar pressure) and consider two drag models: aerodynamic drag and snowplow. There was little difference between these, and their DT profiles matched well with the SMEI data for event 1. Event 2 showed a net acceleration between the LASCO and SMEI FOVs and we could match the data for this event well by introducing a driving Lorentz force. ICME mass almost doubled as a result of swept-up solar wind material from the snowplow model. Finally, we compared the geometry and kinematics of the ICME with that produced by the HAFv2 model and found that the model reasonably matched the geometry, but overestimated the ICME speed.

We analyze the mixed-frame equations of radiation hydrodynamics under the approximations of flux-limited diffusion and a thermal radiation field and derive the minimal set of evolution equations that includes all terms that are of leading order in any regime of nonrelativistic radiation hydrodynamics. Our equations are accurate to first order in v/c in the static diffusion regime. In contrast, we show that previous lower order derivations of these equations omit leading terms in at least some regimes. In comparison to comoving-frame formulations of radiation hydrodynamics, our equations have the advantage that they manifestly conserve total energy, making them very well suited to numerical simulations, particularly with adaptive meshes. For systems in the static diffusion regime, our analysis also suggests an algorithm that is both simpler and faster than earlier comoving-frame methods. We implement this algorithm in the Orion adaptive mesh refinement code and show that it performs well in a range of test problems.

Notwithstanding the advent of the Gamma-ray Large Area Space Telescope, theoretical models predict that a significant fraction of the cosmic γ-ray background (CGB), at a level of 20% of the currently measured value, will remain unresolved. The angular power spectrum of intensity fluctuations of the CGB contains information on its origin. We show that probing the latter on scales from a few tens of arcminutes to several degrees, together with complementary GLAST observations of γ-ray emission from galaxy clusters and the blazar luminosity function, can discriminate between a background that originates from unresolved blazars or cosmic rays accelerated at structure formation shocks.

Using three-dimensional hydrodynamic simulations, we investigate heating and turbulence driving in an intracluster medium (ICM) by orbital motions of galaxies in a galaxy cluster. We consider N_g member galaxies on isothermal and isotropic orbits through an ICM typical of rich clusters. An introduction of the galaxies immediately produces gravitational wakes, providing perturbations that can potentially grow via resonant interaction with the background gas. When NM₁₁ ≲ 100, where M₁₁ is each galaxy mass in units of 10¹¹M_☉, the perturbations are in the linear regime and the resonant excitation of gravity waves is efficient in generating kinetic energy in the ICM, resulting in the velocity dispersion σ_v ~ 2.2NM₁₁ km s^-1. When NM₁₁ ≳ 100, on the other hand, nonlinear fluctuations of the background ICM destroy galaxy wakes and thus render resonant excitation weak or absent. In this case, the kinetic energy saturates at the level corresponding to σ_v ~ 220 km s^-1. The angle-averaged velocity power spectra of turbulence driven in our models have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of resonant excitation, none of the cooling models considered are able to halt the cooling catastrophe, suggesting that the galaxy motions alone are unlikely to solve the cooling flow problem.

We present the IR luminosity function derived from ultradeep 70 μm imaging of the GOODS-North field. The 70 μm observations are longward of the PAH and silicate features which complicate work in the MIR. We derive far-infrared luminosities for the 143 sources with S₇₀ > 2 mJy (S/N > 3 σ). The majority (81%) of the sources have spectroscopic redshifts, and photometric redshifts are calculated for the remainder. The IR luminosity function at four redshifts (z ~ 0.28, 0.48, 0.78, and 0.97) is derived and compared to the local one. There is considerable degeneracy between luminosity and density evolution. If the evolving luminosity function is described as ρ(L, z) = (1 + z)^qρ(L/(1 + z)^p, 0), we find q = -2.19p + 6.09. In the case of pure luminosity evolution, we find a best fit of p = 2.78. This is consistent with the results from 24 μm and 1.4 GHz studies. Our results confirm the emerging picture of strong evolution in LIRGs and ULIRGs at 0.4 < z < 1.1, but we find no evidence of significant evolution in the sub-LIRG (L < 10¹¹L_☉) population for z < 0.4.

We correlate the positions of 13,240 brightest cluster galaxies (BCGs) with 0.1 ≤ z ≤ 0.3 from the maxBCG catalog with radio sources from the FIRST survey to study the sizes and distributions of radio AGNs in galaxy clusters. We find that 19.7% of our BCGs are associated with FIRST sources, and this fraction depends on the stellar mass of the BCG, and to a lesser extent on the richness of the parent cluster (in the sense of increasing radio-loudness with increasing mass). The intrinsic size of the radio emission associated with the BCGs peaks at 55 kpc, with a tail extending to 200 kpc. The radio power of the extended sources places them on the divide between FR I and FR II type sources, while sources compact in the radio tend to be somewhat less radio-luminous. We also detect an excess of radio sources associated with the cluster, instead of with the BCG itself, extending out to ~1.4 Mpc.

Recent Spitzer observations have revealed a substantial population of z ~ 2 ultraluminous infrared galaxies (ULIRGs) with deep silicate absorption (τ_9.7 > 1). This paper reports a 20 cm radio study of such a sample to elucidate their physical nature. We discover that a substantial fraction (40%) of deep silicate absorption ULIRGs at z ~ 2 are moderately radio-loud, with L_1.4GHz = 10²⁵-10²⁶ W Hz^-1. This is in strong contrast with z ≲ 1 radio galaxies and radio-loud quasars where none of the sources with available IRS spectra have τ_9.7 > 1. In addition, we observe radio jets in two of our sources, with one having a double lobe structure ~200 kpc in extent and the other showing a one-sided jet extending ~90 kpc from the nucleus. The likely high inclination of the latter, coupled with its deep silicate absorption, implies the mid-IR obscuration does not share an axis with the radio jets. These sources are highly obscured quasars, observed in the transition stage after the birth of the radio source, but before feedback effects dispel the interstellar medium and halt the black hole accretion and starburst activity.

We report on the discovery of very high energy (VHE) γ-ray emission from the BL Lacertae object 1ES 1011+496. The observation was triggered by an optical outburst in 2007 March and the source was observed with the MAGIC telescope from 2007 March to May. Observing for 18.7 hr, we find an excess of 6.2 σ with an integrated flux above 200 GeV of (1.58 ± 0.32) × 10^-11 photons cm^-2 s^-1. The VHE γ-ray flux is >40% higher than in 2006 March-April (reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES 1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z = 0.212 makes 1ES 1011+496 the most distant source observed to emit VHE γ-rays to date.

We employ X-ray stacking techniques to examine the contribution from X-ray-undetected, mid-infrared-selected sources to the unresolved, hard (6-8 keV) cosmic X-ray background (CXB). We use the publicly available, 24 μm Spitzer Space Telescope MIPS catalogs from the Great Observatories Origins Deep Survey (GOODS)-North and South fields, which are centered on the 2 Ms Chandra Deep Field-North and 1 Ms Chandra Deep Field-South, to identify bright (S_{24 μm} > 80 μJy) mid-infrared sources that may be powered by heavily obscured AGNs. We measure a significant stacked X-ray signal in all of the X-ray bands examined, including, for the first time, a significant (3.2 σ) 6-8 keV stacked X-ray signal from an individually undetected X-ray source population. We find that the X-ray-undetected MIPS sources make up ≈2% (or less) of the total CXB below 6 keV, but ≈6% in the 6-8 keV band. The 0.5-8 keV stacked spectrum is consistent with a hard power law (Γ = 1.44 ± 0.07), with the spectrum hardening at higher X-ray energies. Our findings show that these bright MIPS sources do contain obscured AGNs, but are not the primary source of the unresolved ~40% of 6-8 keV CXB. Our study rules out obscured, luminous quasars as a significant source of the remaining unresolved CXB and suggests that it most likely arises from a large population of obscured, high-redshift (z ≳ 1), Seyfert-luminosity AGNs.

The observed spectra of blazars, their intrinsic emission, and the underlying populations of radiating particles are intimately related. The use of these sources as probes of the extragalactic infrared background, a prospect propelled by recent advances in TeV-band telescopes, soon to be augmented by observations by NASA's upcoming Gamma-Ray Large Area Space Telescope, has been a topic of great recent interest. Here, it is demonstrated that if particles in blazar jets are accelerated at relativistic shocks, then γ-ray spectra with indices less than 1.5 can be produced. This, in turn, loosens the upper limits on the near-infrared extragalactic background radiation previously proposed. We also show evidence hinting that TeV blazars with flatter spectra have higher intrinsic TeV γ-ray luminosities, and we indicate that there may be a correlation of flatness and luminosity with redshift.

We have studied the location of narrow-line Seyfert 1 (NLS1) galaxies and broad-line Seyfert 1 (BLS1) galaxies on the M_BH-σ relation of nonactive galaxies. We find that NLS1 galaxies as a class—as well as the BLS1 galaxies of our comparison sample—do follow the M_BH-σ relation of nonactive galaxies if we use the width of the [S II] λλ6716, 6731 emission lines as a surrogate for stellar velocity dispersion, σ_*. We also find that the width of [O III] λ5007 is a good surrogate for σ_*, but only after (1) removal of asymmetric blue wings and, more importantly, after (2) excluding core [O III] lines with strong blueshifts (i.e., excluding galaxies which have their [O III] velocity fields dominated by radial motions, presumably outflows). The same galaxies which are extreme outliers in [O III] still follow the M_BH-σ relation in [S II]. We systematically investigate the influence of several parameters on the NSL1 galaxies' location on the M_BH-σ plane: [O III]_core blueshift, L/L_Edd, intensity ratio Fe II/Hβ, NLR density, and absolute magnitude. Implications for NLS1 models and for their evolution along the M_BH-σ relation are discussed.

Recent studies indicate that Type Ia supernovae (SNe Ia) consist of two groups—a "prompt" component whose rates are proportional to the host galaxy star formation rate, whose members have broader light curves and are intrinsically more luminous, and a "delayed" component whose members take several Gyr to explode, have narrower light curves, and are intrinsically fainter. As cosmic star formation density increases with redshift, the prompt component should begin to dominate. We use a two-component model to predict that the average light curve width should increase by 6% from z = 0 to 1.5. Using data from various searches, we find an 8.1% ± 2.7% increase in average light curve width for non-subluminous SNe Ia from z = 0.03 to 1.12, corresponding to an increase in the average intrinsic luminosity of 12%. To test whether there is any bias after supernovae are corrected for light curve shape we use published data to mimic the effect of population evolution and find no significant difference in the measured dark energy equation of state parameter, w. However, future measurements of time-variable w will require standardization of SN Ia magnitudes to 2% up to z = 1.7, and it is not yet possible to assess whether light curve shape correction works at this level of precision. Another concern at z = 1.5 is the expected order-of-magnitude increase in the number of SNe Ia that cannot be calibrated by current methods.

We studied the properties of the intracluster medium (ICM) in two clusters of galaxies (AWM 7 and Abell 1060) and two groups (HCG 62 and NGC 507) with the X-ray observatory Suzaku. Based on spatially resolved energy spectra, we measured for the first time precise cumulative ICM metal masses within 0.1 and ~0.3r₁₈₀. Comparing our results with supernova nucleosynthesis models, the number ratio of Type II (SNe II) to Type Ia (SNe Ia) is estimated to be ~3.5, assuming the metal mass in the ICM is represented by the sum of products synthesized in SNe Ia and SNe II. Normalized by the K-band luminosities of present galaxies, and including the metals in stars, the integrated number of past SN II explosions is estimated to be close to or somewhat higher than the star formation rate determined from Hubble Deep Field observations.

I consider in light of MOND the three debris galaxies discussed recently by Bournaud et al. These exhibit mass discrepancies of a factor of a few within several scale lengths of the visible galaxy, which, arguably, is contrary to the expectations from the cold dark matter paradigm. I show here that the rotational velocities predicted by MOND agree well with the observed velocities for each of the three galaxies, with only the observed baryonic matter as the source of gravity. There is thus no need to invoke a new form of baryonic, yet-undetected matter that dominates the disk of spiral galaxies, as advocated by Bournaud et al. I argue on other grounds that the presence of such ubiquitous disk dark matter, in addition to cold dark matter, is not likely.

We use the Hubble Space Telescope ACS to study the resolved stellar populations of the nearby, nearly edge-on galaxy NGC 4244 across its outer disk surface density break. The stellar photometry allows us to study the distribution of different stellar populations and reach very low equivalent surface brightnesses. We find that the break occurs at the same radius for young, intermediate-age, and old stars. The stellar density beyond the break drops sharply by a factor of at least 600 in 5 kpc. The break occurs at the same radius independent of height above the disk, but is sharpest in the midplane and nearly disappears at large heights. These results make it unlikely that truncations are caused by a star formation threshold alone: the threshold would have to keep the same radial position from less than 100 Myr to 10 Gyr ago, in spite of potential disturbances such as infall and redistribution of gas by internal processes. A dynamical interpretation of truncation formation is more likely, such as due to angular momentum redistribution by bars or density waves, or heating and stripping of stars caused by the bombardment of dark matter subhalos. The latter explanation is also in quantitative agreement with the small diffuse component we see around the galaxy.

We present stellar velocity dispersion profiles for seven Milky Way dwarf spheroidal (dSph) satellite galaxies. We have measured 8394 line-of-sight velocities (±2.5 km s^-1) for 6804 stars from high-resolution spectra obtained at the Magellan and MMT telescopes. We combine these new data with previously published velocities to obtain the largest available kinematic samples, which include more than 5500 dSph members. All the measured dSphs have stellar velocity dispersion of order 10 km s^-1 that remains approximately constant with distance from the dSph center, out to and in some cases beyond the radius at which the mean surface brightness falls to the background level. Assuming dSphs reside within dark matter halos characterized by the NFW density profile, we obtain reasonable fits to the empirical velocity dispersion profiles. These fits imply that, among the seven dSphs, M_vir ~ 10⁸-10⁹M_☉. The mass enclosed at a radius of 600 pc, the region common to all data sets, lies in the range (2-7) × 10⁷M_☉.

As part of the ACS Survey of Galactic Globular Clusters, we present new Hubble Space Telescope photometry of the massive globular cluster M54 (NGC 6715) and the superposed core of the tidally disrupted Sagittarius (Sgr) dSph galaxy. Our deep (F606W ~ 26.5), high-precision photometry yields an unprecedentedly detailed color-magnitude diagram showing the extended blue horizontal branch and multiple main sequences of the M54+Sgr system. The distance and reddening to M54 are revised using both isochrone and main-sequence fitting to (m - M)₀ = 17.27 and E(B - V) = 0.15. Preliminary assessment finds the M54+Sgr field to be dominated by the old metal-poor populations of Sgr and the globular cluster. Multiple turnoffs indicate the presence of at least two intermediate-aged star formation epochs with 4 and 6 Gyr ages and [Fe/H] = -0.4 to -0.6. We also clearly show, for the first time, a prominent, ~2.3 Gyr old Sgr population of near-solar abundance. A trace population of even younger (~0.1-0.8 Gyr old), more metal-rich ([Fe/H] ~ 0.6) stars is also indicated. The Sgr age-metallicity relation is consistent with a closed-box model and multiple (4-5) star formation bursts over the entire life of the satellite, including the time since Sgr began disrupting.

We present a new, deep (V ~ 26) study of the Galactic globular cluster NGC 2419 based on B, V, I time-series CCD photometry over about 10 years and extending beyond the cluster published tidal radius. We have identified 101 variable stars, of which 60 are new discoveries, doubling the known RR Lyrae stars and including 12 SX Phoenicis stars. The average period of the RR Lyrae stars (⟨P_ab⟩ = 0.662 days and ⟨P_c⟩ = 0.366 days, for fundamental-mode—RRab—and first-overtone pulsators, respectively) and the position in the period-amplitude diagram both confirm that NGC 2419 is an Oosterhoff II cluster. The average apparent magnitude of the RR Lyrae stars is ⟨V⟩ = 20.31 ± 0.01 (σ = 0.06, 67 stars) and leads to the distance modulus μ₀ = 19.60 ± 0.05. The color-magnitude diagram, reaching about 2.6 mag below the cluster turnoff, does not show clear evidence of multiple stellar populations. Cluster stars are found until r ~ 10.5', and possibly as far as r ~ 15', suggesting that the literature tidal radius might be underestimated. No extratidal structures are clearly detected in the data. NGC 2419 has many blue stragglers and a well-populated horizontal branch extending from the RR Lyrae stars down to an extremely blue tail ending with the "blue hook," for the first time recognized in this cluster. The red giant branch is narrow, ruling out significant metallicity spreads. Our results seem to disfavor the interpretation of NGC 2419 as either having an extragalactic origin or being the relict of a dwarf galaxy tidally disrupted by the Milky Way.

We have detected the J = 7-6, 8-7, and 15-14 lines of C₆H^- toward a low-mass star-forming region of L1527. We have also detected the J = 15/2-13/2 and 33/2-31/2 lines of the corresponding neutral species, C₆H, and the 8_1,8-7_1,7 line of C₆H₂ in L1527. This is the first detection of these three species in star-forming regions. The column density of C₆H^- is (5.8 ± 1.8) × 10¹⁰ cm^-2, which is comparable to that in TMC-1, although the column density of C₆H in L1527 is about 1/5 of that in TMC-1. Hence, the N(C₆H^-)/N(C₆H) ratio is 0.093 ± 0.029, which is higher than that in TMC-1 by a factor of 4. This high anion-to-neutral ratio is discussed in terms of a simplified chemical model.

Pulsar emission should come primarily from the magnetic separatrix. Combining theory and observations, we show that force-free electrodynamics (FFE) gives an accurate description of the large-scale electromagnetic field in the magnetospheres of Crab-like pulsars. A robust prediction of FFE is the existence and stability of a singular current layer on the magnetic separatrix. We argue that most of the observed pulsar emission comes from this singular current layer.

Anomalous X-ray pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spin-downs. However, an unambiguous measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report a spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling, B = (2.72 ± 0.03) × 10¹⁴ G, is remarkably close to the value inferred from the rate of spin-down of this source and remains nearly constant during numerous observations spanning over an order of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behavior of AXPs.

PSR B0540-69 is the Crab twin in the Large Magellanic Cloud. The age and energetic and overall behavior of the two pulsars are very similar. The same is true for the general appearance of their pulsar wind nebulae (PWNe). Analysis of Hubble Space Telescope images spanning 10 yr unveiled significant variability in the PWN surrounding PSR B0540-69, with a hot spot moving at ~0.04c. Such behavior, reminiscent of the variability observed in the Crab Nebula along the counterjet direction, may suggest an alternative scenario for the geometry of the system. The same data were used to assess the pulsar proper motion. The null displacement recorded over 10 yr allowed us to set a 3 σ upper limit of 290 km s^-1 to the pulsar velocity.

The fluorine abundance of the carbon-enhanced metal-poor (CEMP) star HE 1305+0132 has been derived by analysis of the molecular HF (1-0) R9 line at 2.3357 μm in a high-resolution (R = 50,000) spectrum obtained with the Phoenix spectrometer and Gemini-South telescope. Our abundance analysis makes use of a CNO-enhanced ATLAS12 model atmosphere characterized by a metallicity and CNO enhancements determined utilizing medium-resolution (R = 3000) optical and near-IR spectra. The effective iron abundance is found to be [Fe/H] = -2.5, making HE 1305+0132 the most Fe-deficient star, by more than an order of magnitude, for which the abundance of fluorine has been measured. Using spectral synthesis, we derive a supersolar fluorine abundance of A(¹⁹F) = 4.96 ± 0.21, corresponding to a relative abundance of [F/Fe] = +2.90. A single line of the Phillips C₂ system is identified in our Phoenix spectrum, and along with multiple lines of the first-overtone vibration-rotation CO (3-1) band head, C and O abundances of A(¹²C) = 8.57 ± 0.11 and A(¹⁶O) = 7.04 ± 0.14 are derived. We consider the striking fluorine overabundance in the framework of the nucleosynthetic processes thought to be responsible for the C-enhancement of CEMP stars and conclude that the atmosphere of HE 1305+0132 was polluted via mass transfer by a primary companion during its asymptotic giant branch phase. This is the first study of fluorine in a CEMP star, and it demonstrates that this rare nuclide can be a key diagnostic of nucleosynthetic processes in the early Galaxy.

Using the Spitzer IRAC camera we have obtained mid-IR photometry of the red giant branch stars in the Galactic globular cluster 47 Tuc. About 100 stars show an excess of mid-IR light above that expected from their photospheric emission. This is plausibly due to dust formation in mass flowing from these stars. This mass loss extends down to the level of the horizontal branch and increases with luminosity. The mass loss is episodic, occurring in only a fraction of stars at a given luminosity. Using a simple model and our observations we derive mass-loss rates for these stars. Finally, we obtain the first empirical mass-loss formula calibrated with observations of Population II stars. The dependence on luminosity of our mass-loss rate is considerably shallower than the widely used Reimers law. The results presented here are the first from our Spitzer survey of a carefully chosen sample of 17 Galactic globular clusters, spanning the entire metallicity range from about one hundredth up to almost solar.

Using the HiVIS spectropolarimeter built for the Haleakala 3.7 m AEOS telescope, we have obtained a large number of high-precision spectropolarimetrc observations (284) of Herbig AeBe stars collected over 53 nights totaling more than 300 hr of observing. Our sample of five HAeBe stars, AB Aurigae, MWC 480, MWC 120, MWC 158, and HD 58647, all show systematic variations in the linear polarization amplitude and direction as a function of time and wavelength near the Hα line. In all our stars, the Hα line profiles show evidence of an intervening disk or outflowing wind, evidenced by strong emission with an absorptive component. The linear polarization varies by 0.2%-1.5% with the change typically centered in the absorptive part of the line profile. These observations are inconsistent with a simple disk-scattering model or a depolarization model that produce polarization changes centered on the emissive core. We speculate that polarized absorption via optical pumping of the intervening gas may be the cause.

A nonlocal cascade model for anisotropic magnetohydrodynamic (MHD) turbulence in the presence of a uniform magnetic field B is proposed. The model takes into account that (1) energy cascades in an anisotropic manner, and as a result a different estimate for the cascade rate in the direction parallel and perpendicular to the B field is made, and (2) the interactions that result in the cascade are between different scales. Eddies with wavenumbers k_∥ and k_⊥ interact with eddies with wavenumbers q_∥, q_⊥ such that a resonance condition between the wavenumbers q_∥, q_⊥ and k_∥, k_⊥ holds. As a consequence, energy from the eddy with wavenumbers k_∥ and k_⊥ cascades due to interactions with eddies located in the resonant manifold whose wavenumbers are determined by q_∥ ≃ ^1/3k/B and q_⊥ ≃ k_⊥, and energy will cascade along the lines k_∥ ≃ k₀ + k^1/3/B. For a uniform energy injection rate in the parallel direction, the resulting energy spectrum is E(k_∥,k_⊥) ≃ ^2/3kk. For a general forcing, however, the model suggests a nonuniversal behavior. The connections with previous models, numerical simulations and weak turbulence theory are discussed.

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and IMF, providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

With the assumption of radial motion and uniform longitudinal distribution of coronal mass ejections (CMEs), we propose a method to eliminate projection effects from the apparent observed CME latitude distribution. This method has been applied to SOHO LASCO data from 1996 January to 2006 December. As a result, we find that the real CME latitude distribution had the following characteristics: (1) High-latitude CMEs (θ > 60°, where θ is the latitude) constituted 3% of all CMEs and mainly occurred during the time when the polar magnetic fields reversed sign. The latitudinal drift of the high-latitude CMEs was correlated with that of the heliospheric current sheet. (2) Four percent of all CMEs occurred in the range 45° ≤ θ ≤ 60°. These midlatitude CMEs occurred primarily in 2000, near the middle of 2002, and in 2005, forming a prominent three-peak structure. (3) The highest occurrence probability of low-latitude (θ < 45°) CMEs was at the minimum and during the declining phase of the solar cycle. However, the highest occurrence rate of low-latitude CMEs was at the maximum and during the declining phase of the solar cycle. The latitudinal evolution of low-latitude CMEs did not follow the Spörer sunspot law, which suggests that many CMEs originated outside of active regions.

For the first time, we present a rare observation of direct magnetic interaction between an erupting filament and a coronal hole (CH). The small active region filament obliquely erupted toward the CH getting in the way, met and interacted with it, and then was deflected back. The erupting filament thus underwent a distinct to-and-fro motion in the visible disk, while the CH was clearly disturbed by the interaction. Brightenings in Hα and EUV and darkenings in He I 10830 Å appeared at the boundaries and in the interior of the CH. This eruption was closely associated with the initiation of a halo-type coronal mass ejection (CME). The direction of the CME, despite being greatly different from that of the initial filament eruption, was consistent with that of the reflected filament. Moreover, when the CME was seen in the limb, the filament was still in the process of the return journey in the visible disk. Therefore, it appears that the large-scale structure of the CME was bounced against and then reflected away from the CH along with the filament, and the eruptive filament represented only a very small part in the CME.

We discuss nonthermal velocities in an active region as revealed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The velocities are derived from spectral line profiles in the extreme-ultraviolet (EUV) from a strong line of Fe XII at 195.12 Å by fitting each line profile to a Gaussian function. We compare maps of the full width at half-maximum values, the Fe XII spectral line intensity, the Fe XII Doppler shift, the electron temperature, and electron density. We find that the largest widths in the active region do not occur in the most intense regions, but seem to concentrate in less intense regions, some of which are directly adjacent to coronal loops, and some of which concentrate in regions which also exhibit relative Doppler outflows. The increased widths can also occur over extended parts of the active region.

This Letter discusses the role of a weak toroidal magnetic field in modifying the turbulent transport properties of stably stratified rotating turbulence in the tachocline. A local two-dimensional β-plane model is investigated numerically. In the absence of magnetic fields, nonlinear interactions of Rossby waves lead to the formation of strong mean zonal flows. However, the addition of even a very weak toroidal field suppresses the generation of mean flows. We argue that this has serious implications for angular momentum transport in the lower tachocline.