Table of contents

Combined with other cosmic microwave background experiments, the Wilkinson Microwave Anisotropy Probe (WMAP) survey provides an accurate estimate of the baryon density of the universe. In the framework of the standard big bang nucleosynthesis (BBN), such a baryon density leads to predictions for the primordial abundances of ⁴He and D in good agreement with observations. However, it also leads to a significant discrepancy between the predicted and observed primordial abundance of ⁷Li. Such a discrepancy is often termed "the lithium problem." In this paper we analyze this problem in the framework of scalar tensor theories of gravity. It is shown that an expansion of the universe slightly slower than in general relativity before BBN, but faster during BBN, solves the lithium problem and leads to ⁴He and D primordial abundances consistent with the observational constraints. This kind of behavior is obtained in numerous scalar tensor models, both with and without a self-interaction potential for the scalar field. In models with a self-interacting scalar field, the convergence toward general relativity is ensured without any condition, thanks to an attraction mechanism that starts to work during the radiation-dominated epoch.

On the one hand, the large-scale structure of matter is arguably scale invariant, and on the other hand, halos and voids are recognized as prominent features of that structure. To unify both approaches, we propose to model the dark matter distribution as a set of fractal distributions of halos of different kinds. This model relies on the concept of a multifractal as the most general scaling distribution and on a plausible notion of a halo as a singular mass concentration in a multifractal. Voids arise as complementary to halos, namely, as formed by regular mass depletions. To provide halos with definite size and masses, we coarse-grain the dark matter distribution using a natural length derived from the lower scaling limit. This allows us to relate the halo mass function to the multifractal spectrum. Hence, we find that a lognormal model of the mass distribution nicely fits in this picture and, moreover, the Press-Schechter mass function can be recovered as a bifractal limit. To support our model of fractal distributions of halos, we perform a numerical study of the distribution produced in cosmological N-body simulations. In the Virgo ΛCDM GIF2 simulation, we indeed find fractal distributions of halos with various dimensions and a halo mass function of bifractal type. However, this mass function is just beyond the Press-Schechter's range, and we interpret it instead as caused by the undersampling of the distribution at the scale of halos, due to discretization.

Based on the Beylkin-Cramer summation rule, we introduce a new fast algorithm that enables us to explore the high-order statistics efficiently in large data sets. Central to this technique is to make decompositions both of fields and operators within the framework of multiresolution analysis and to realize their discrete representations. Accordingly, a homogeneous point process could be equivalently described by the operation of a Toeplitz matrix on a vector, which is accomplished by making use of the fast Fourier transformation. The algorithm could be applied widely in cosmic statistics to tackle large data sets. We demonstrate this novel technique using the spherical, cubic, and cylindrical counts in cells. The numerical test shows that the algorithm produces an excellent agreement with the expected results. Moreover, the algorithm naturally introduces a sharp filter, which is capable of suppressing shot noise in weak signals. In the numerical procedures, the algorithm is somewhat similar to particle-mesh methods in N-body simulations. Since it is scaled with O(N log N), it is significantly faster than the current particle-based methods, and its computational cost does not rely on the shape or size of the sampling cells. In addition, based on this technique, we further propose a simple fast scheme to compute the second statistics for cosmic density fields and justify it using simulation samples. Hopefully, the technique developed here allows us to make a comprehensive study of non-Gaussianity of the cosmic fields in high-precision cosmology. A specific implementation of the algorithm is publicly available on request to the author.

We have developed an analytical model to describe the evolution of anisotropic galactic outflows. With it we investigate the impact of varying opening angle on galaxy formation and the evolution of the intergalactic medium. We have implemented this model in a Monte Carlo algorithm to simulate galaxy formation and outflows in a cosmological context. Using this algorithm, we have simulated the evolution of a comoving volume of size (12 h^-1 Mpc)³ in the ΛCDM universe. Starting from a Gaussian density field at redshift z = 24, we follow the formation of ~20,000 galaxies and simulate the galactic outflows produced by these galaxies. When these outflows collide with density peaks, ram pressure stripping of the gas inside the peaks may result. This occurs in around half the cases and prevents the formation of galaxies. Anisotropic outflows follow the path of least resistance and thus travel preferentially into low-density regions, away from cosmological structures (filaments and pancakes) in which galaxies form. As a result, the number of collisions is reduced, leading to the formation of a larger number of galaxies. Anisotropic outflows can significantly enrich low-density systems with metals. Conversely, the cross pollution in metals of objects located in a common cosmological structure, like a filament, is significantly reduced. Highly anisotropic outflows can travel across cosmological voids and deposit metals in other, unrelated cosmological structures.

Gravitational waves emitted by chirping supermassive black hole binaries could in principle be used to obtain very accurate distance determinations. Provided they have an electromagnetic counterpart from which the redshift can be determined, these standard sirens could be used to build a high-redshift Hubble diagram. Errors in the distance measurements will most likely be dominated by gravitational lensing. We show that the (de)magnification due to inhomogeneous foreground matter will increase the scatter in the measured distances by a factor of ~10. We propose to use optical and IR data of the foreground galaxies to minimize the degradation from weak lensing. We find that the net effect of correcting the estimated distances for lensing is comparable to increasing the sample size by a factor of 3 when using the data to constrain cosmological parameters.

We employ N-body, smoothed particle hydrodynamic simulations, including detailed treatment of chemical enrichment, to follow a gas-rich merger that results in a galaxy with disk morphology. We trace the kinematic, structural, and chemical properties of stars formed before, during, and after the merger. We show that such a merger produces two exponential disk components, with the older, hotter component having a scale length 20% larger than the later forming, cold disk. Rapid star formation during the merger quickly enriches the protogalactic gas reservoir, resulting in high metallicities of the forming stars. These stars form from gas largely polluted by Type II supernovae, which form rapidly in the merger-induced starburst. After the merger, a thin disk forms from gas that has had time to be polluted by Type Ia supernovae. Abundance trends are plotted, and we examine the proposal that increased star formation during gas-rich mergers may explain the high α-to-iron abundance ratios that exist in the relatively high-metallicity, thick-disk component of the Milky Way.

With the aid of a simple yet robust approach, we investigate the influence of dissipationless and dissipative merging on galaxy structure and the consequent effects on the scaling laws followed by elliptical galaxies. Our results suggest that elliptical galaxies cannot be originated by parabolic merging of low-mass spheroids only, even in the presence of substantial gas dissipation. However, we also found that scaling laws such as the Faber-Jackson, Kormendy, fundamental plane, and M_BH-σ relations, when considered over the whole mass range spanned by elliptical galaxies in the local universe, are robust against merging. We conclude that galaxy scaling laws, possibly established at high redshift by the fast collapse in preexisting dark matter halos of gas-rich and clumpy stellar distributions, are compatible with a (small) number of galaxy mergers at lower redshift.

We present 0.1'' resolution near-infrared integral field spectroscopy of Hα in a z = 1.4781 star-forming galaxy, Q2343-BM133. These observations were obtained with the OH Suppressing Infra-Red Imaging Spectrograph (OSIRIS) using the W. M. Keck Observatory laser guide star adaptive optics (LGS AO) system. Hα emission is resolved over a 0.8''(6.8 kpc) × 0.5''(4.3 kpc) region with a 0.1'' spatial resolution. We find a global flux of 4.2 ± 0.6 × 10^-16 ergs s^-1 cm^-2, and detect a spatially resolved velocity gradient of ~134 km s^-1 across the galaxy and a global velocity dispersion of 73 ± 9 km s^-1. An upper limit of [N ]/Hα ≲ 0.12 is inferred, which implies that this galaxy is not dominated by an active galactic nucleus and has a metallicity at or below 1/2 solar metallicity. We derive a star formation rate (SFR) of 47 ± 6 M_☉ yr^-1 and a dereddened SFR of 66 ± 9 M_☉ yr^-1. Two-dimensional kinematics for Q2343-BM133 fit well with an inclined disk model, with which we estimate an enclosed mass of 4.3 × 10⁹M_☉ within 5.5 kpc. A possible merger scenario is also presented, and cannot be fully ruled out. We derive a virial mass of 1.1 × 10¹⁰M_☉ for a disk geometry, using the observed velocity dispersion. We propose that Q2343-BM133 is currently at an early stage of disk formation at a look-back time of 9.3 Gyr.

Using ~300,000 photometrically classified quasars, by far the largest quasar sample ever used for such analyses, we study the redshift and luminosity evolution of quasar clustering on scales of ~50 h^-1 kpc to ~20 h^-1 Mpc from redshifts of ~ 0.75-2.28. We parameterize our clustering amplitudes using realistic dark matter models and find that a ΛCDM power spectrum provides a superb fit to our data with a redshift-averaged quasar bias of b = 2.41 ± 0.08 (P_<χ² = 0.847) for σ₈ = 0.9. This represents a better fit than the best-fit power-law model [ω = (0.0493 ± 0.0064) θ^{-0.928±0.055}; P_<χ² = 0.482]. We find b_Q increases with redshift. This evolution is significant at >99.6% using our data set alone, increasing to >99.9999% if stellar contamination is not explicitly parameterized. We measure the quasar classification efficiency across our full sample as a = 95.6 ± %, a star-quasar separation comparable to the star-galaxy separation in many photometric studies of galaxy clustering. We derive the mean mass of the dark matter halos hosting quasars as M_DMH = (5.2 ± 0.6) × 10¹²h^-1M_☉. At ~ 1.9 we find a 1.5 σ deviation from luminosity-independent quasar clustering; this suggests that increasing our sample size by a factor of ~1.8 could begin to constrain any luminosity dependence in quasar bias at z ~ 2. Our results agree with recent studies of quasar environments at z < 0.4, which detected little luminosity dependence to quasar clustering on proper scales ≳50 h^-1 kpc. At z < 1.6, our analysis suggests that b_Q is constant with luminosity to within Δb_Q ~ 0.6, and that, for g < 21, angular quasar autocorrelation measurements are unlikely to have sufficient statistical power at z ≲ 1.6 to detect any luminosity dependence in quasars' clustering.

We study quasar clustering on small scales, modeling clustering amplitudes using halo-driven dark matter descriptions. From 91 pairs on scales <35 h^-1 kpc, we detect only a slight excess in quasar clustering over our best-fit large-scale model. Integrated across all redshifts, the implied quasar bias is b_Q = 4.21 ± 0.98 (b_Q = 3.93 ± 0.71) at ~18 h^-1 kpc (~28 h^-1 kpc). Our best-fit (real space) power index is ~-2 [i.e., ξ(r) ∝ r^-2], implying steeper halo profiles than currently found in simulations. Alternatively, quasar binaries with separation <35 h^-1 kpc may trace merging galaxies, with typical dynamical merger times t_d ~ (610 ± 260)m^-1/2h^-1 Myr, for quasars of host halo mass m × 10¹²h^-1M_☉. We find that UV-excess quasars at ~28 h^-1 kpc cluster >5 times higher at z > 2 than at z < 2, at the 2.0 σ level. However, as the space density of quasars declines as z increases, an excess of quasar binaries (over expectation) at z > 2 could be consistent with reduced merger rates at z > 2 for the galaxies forming UV-excess quasars. Comparing our clustering at ~28 h^-1 kpc to a ξ(r) = (r/4.8 h^-1 Mpc)^-1.53 power law, we find an upper limit on any excess of a factor of 4.3 ± 1.3, which, noting some caveats, differs from large excesses recently measured for binary quasars, at 2.2 σ. We speculate that binary quasar surveys that are biased to z > 2 may find inflated clustering excesses when compared to models fit at z < 2. We provide details of 111 photometrically classified quasar pairs with separations <0.1'. Spectroscopy of these pairs could significantly constrain quasar dynamics in merging galaxies.

A recent study suggests that the quasar HE 0450-2958 is hosted by a galaxy substantially fainter than that inferred from the correlation between black hole mass and bulge luminosity. As this result has significant bearings on galaxy and black hole evolution, we revisit the issue by performing an independent analysis of the data, using a two-dimensional image fitting technique. We indeed find no evidence of a host galaxy either, but due to the brightness of the quasar and uncertainties in the point-spread function, the limits are fairly weak. To derive an upper limit on the host galaxy luminosity, we perform simulations to deblend the quasar from the host under conditions similar to those actually observed. We find that the host galaxy has an absolute magnitude upper limit of -20 ≲ M_V ≲ -21, in good agreement with the previous determination. Since this limit is consistent with the value predicted from the current best estimate of the black hole mass, there is no compelling evidence that the quasar HE 0450-2958 has an abnormally underluminous host galaxy. We also show that, contrary to previous claims, the companion galaxy to HE 0450-2958 should not be regarded as an ultraluminous infrared galaxy.

A magnetic field dynamo in the inner regions of the accretion disk surrounding the supermassive black holes in AGNs may be the mechanism that generates magnetic fields in galaxies and in extragalactic space. We argue that the two coherent motions produced by (1) the Keplerian motion and (2) star-disk collisions, numerous in the inner region of AGN accretion disks, are both basic to the formation of a robust, coherent dynamo and consequently to the generation of large-scale magnetic fields. Star-disk collisions are frequent enough to account for an integrated dynamo gain, e¹⁰⁹ at 100 gravitational radii of a central black hole, many orders of magnitude greater than what is required to amplify any seed field, no matter how small. The existence of extragalactic, coherent, large-scale magnetic fields whose energies greatly exceed all but massive black hole energies is recognized. In Paper II we argue that in order to produce a dynamo that can access the free energy of black hole formation and produce all the magnetic flux in a coherent fashion, the existence of these two coherent motions in a conducting fluid is required. The differential winding of Keplerian motion is obvious; the counter-rotation of driven plumes in a rotating frame is less well known, but has been previously demonstrated in laboratory modeling. The disk structure depends on the model of α, the transport coefficient of angular momentum chosen, but fortunately the magnetic effect is independent of the disk model. Both motions are discussed in this paper. The description is preliminary to two theoretical derivations and one numerical simulation of the α-ω dynamo in Paper II.

We show that a dynamo can be produced in an active galactic nucleus (AGN) accretion disk by the Keplerian shear and the helical motions of expanding and twisting plumes of plasma heated by many star passages through the disk. Each plume rotates a fraction of the toroidal flux into poloidal flux, always in the same direction, through a finite angle, and proportional to its diameter. The predicted growth rate of poloidal magnetic flux, based on two analytic approaches and numerical simulations, leads to a rapid exponentiation of a seed field, ~0.1 to ~0.01 per Keplerian period at the inner part of the disk. The initial value of the seed field may therefore be arbitrarily small, yet through dynamo gain reach saturation very early in the disk history. Because of tidal disruption of stars close to the black hole, the maximum growth rate occurs at a radius of about 100 gravitational radii from the central object. The generated mean magnetic field, a quadrupole field, has predominantly even parity, so that the radial component does not reverse sign across the midplane. The linear growth is predicted to be the same by three different theoretical analyses: the flux conversion model, the mean field approach, and numerical modeling. The common feature is the conducting fluid flow (considered in Paper I), where two coherent large-scale flows occur naturally, the differential winding of Keplerian motion and differential rotation of expanding plumes.

We present a statistical analysis of the photometric properties and spatial distribution of more than 2800 Mg II absorbers with 0.37 < z < 1 and rest equivalent width W₀(λ2796) > 0.8 Å detected in SDSS quasar spectra. Using an improved image-stacking technique, we measure the cross-correlation between Mg II gas and light (in the g, r, i and z bands) from 10 to 200 kpc and infer the light-weighted impact parameter distribution of Mg II absorbers. This quantity is well described by a power law with an index that strongly depends on absorption rest equivalent width W₀, ranging from ~-1 for W₀ ≲ 1 Å to ~-2 for W₀ ≳ 1.5 Å. At redshift 0.37 < z_abs ≤ 0.55, we find the average luminosity enclosed within 100 kpc around Mg II absorbers to be M_g = -20.65 ± 0.11 mag, which is ~0.5L. The global luminosity-weighted colors are typical of present-day intermediate-type galaxies. We then investigate these colors as a function of Mg II rest equivalent width and find that they follow the track between spiral and elliptical galaxies in color space; while the light of weaker absorbers originates mostly from red passive galaxies, stronger systems display the colors of blue star-forming galaxies. We argue that the origin of strong Mg II absorber systems might be better explained by models of metal-enriched gas outflows from star-forming/bursting galaxies. No significant redshift dependence for both impact parameter and rest-frame colors is observed up to z = 1. However, we do observe a brightening of the absorbers' related light at high redshift (~50% from z_abs ~ 0.4 to 1). We argue that Mg II absorbers are a phenomenon typical of a given evolutionary phase that more massive galaxies experience earlier than less massive ones, in a "downsizing" fashion.

We present r'- or i'-band WIYN images of the fields of 15 Sloan Digital Sky Survey quasars that have spectra exhibiting intervening Mg II absorption-line systems with rest equivalent widths 2.7 Å ≤ W ≤ 6.0 Å and redshifts 0.42 < z_abs < 0.84. Such systems are rare and exhibit projected absorption velocity spreads in excess of ≈300-650 km s^-1. Approximately 60% are expected to be damped Lyα systems. In each of our fields we detect at least one galaxy that, if at the absorption redshift, would have impact parameter b ≲ 40 kpc and luminosity L ≳ 0.3L*. We measure a significant excess of galaxies at low b to the sight lines over a large range of luminosity. Many of the sight lines are found to pass either through or close to the optically luminous extent of a galaxy. Considering the very large velocity spreads seen in absorption, this suggests that these absorbing regions are more kinematically complex than local spirals such as the Milky Way. Our data indicate that interactions and galaxy pairs may be a contributing factor to the production of such large velocity spreads. Finally, we also find evidence that a population of galaxies with luminosities in the range 4L* ≲ L ≲ 13L* may contribute to the presence of ultrastrong Mg II absorption. Thus, some of the absorbing galaxies may represent a population intermediate to the very luminous high-redshift Lyman break galaxies and the fainter local starburst population.

We present the first results of the VLBA Imaging and Polarimetry Survey (VIPS), a 5 GHz VLBI survey of 1127 sources with flat radio spectra. Through automated data reduction and imaging routines, we have produced publicly available I, Q, and U images and have detected polarized flux density from 37% of the sources. We have also developed an algorithm to use each source's I image to automatically classify it as a pointlike source, a core jet, a compact symmetric object (CSO) candidate, or a complex source. Using data from the Sloan Digital Sky Survey (SDSS), we have found no significant trend between optical flux and 5 GHz flux density for any of the source categories. Using the velocity width of the Hβ emission line and the monochromatic luminosity at 5100 Å to estimate the central black hole mass, M_BH, we have found a weak trend between M_BH and 5 GHz luminosity density for objects with SDSS spectra. The mean ratio of the polarized to total 5 GHz flux density for VIPS sources with detected polarized flux density ranges from 1% to 20% with a median value of about 5%. We have also found significant evidence that the directions of the jets in core-jet systems tend to be perpendicular to the electric vector position angles (EVPAs). The data are consistent with a scenario in which ~24% of the polarized core jets have EVPAs that are antialigned with the directions of their jet components and that have a substantial amount of Faraday rotation. In addition to these initial results, plans for future follow-up observations are discussed.

We investigate aspects of the cosmological evolution of FR II radio galaxies, focusing first on the abilities of models to match data for linear sizes, radio powers, redshifts, and spectral indices. Here we consider modifications to the theoretical models we had treated earlier, primarily by accounting for the growth of the radius of hot spots with source size. Better fits to the distributions of most of the data in three low-frequency surveys can be found with sensible choices of model parameters, but no model yet considered gives a good match to all of the survey data simultaneously, nor does any do a good job of producing the spectral index distributions. The observational data sets are too small to completely discriminate among the models. We calculate the volume fraction of the "relevant universe" cumulatively occupied by the expanding radio galaxy lobes over the quasar era, when these powerful radio galaxies were much more common, and when they have been argued to play an important role in triggering galaxy formation and spreading magnetic fields and metals. We found the cumulative relevant volume filling factor of radio galaxies to be ~5%, so we conclude that these impacts are smaller than previously estimated but that they are still significant.

Relations between the observed quantities for a beamed radio jet, which are the apparent transverse speed and the apparent luminosity (β_app, L), and the intrinsic quantities, which are the Lorentz factor and the intrinsic luminosity (γ, L₀), are investigated. The inversion from measured to intrinsic values is not unique, but approximate limits to γ and L₀ can be found using probability arguments. Roughly half the sources in a flux density-limited, beamed sample have a value of γ close to the measured value of β_app. The methods are applied to observations of 119 AGN jets made with the VLBA at 15 GHz during 1994-2002. The results strongly support the common relativistic beam model for an extragalactic radio jet. The (β_app, L) data are closely bounded by a theoretical envelope, an "aspect" curve for γ = 32 and L₀ = 10²⁵ W Hz^-1. This gives limits to the maximum values of γ and L₀ in the sample: γ_max ≈ 32, and L_0,max ~ 10²⁶ W Hz^-1. No sources with both high values of β_app and low values of L are observed. This is not the result of selection effects due to the observing limits, which are a flux density of S > 0.5 Jy and an angular velocity of μ < 4 mas yr^-1. Many of the fastest quasars have a pattern Lorentz factor, γ_p, that is close to that of the beam, γ_b, but some of the slow quasars must have γ_p ≪ γ_b. Three of the 10 galaxies in the sample have a superluminal feature, with speeds up to β_app ≈ 6. The others are at most mildly relativistic. The galaxies are not off-axis versions of the powerful quasars, but Cygnus A might be an exception.

Using the Major Atmospheric Gamma Imaging Cerenkov Telescope (MAGIC), we have observed the nearest ultraluminous infrared galaxy, Arp 220, for about 15 hr. No significant signal was detected within the dedicated amount of observation time. The first upper limits to the very high energy γ-ray flux of Arp 220 are herein reported and compared with theoretical expectations.

We present multiwavelength observations of the very luminous "E+A" galaxy known as G515 (J152426.50+080908.0), including deep K_s imaging, spatially resolved Hα spectroscopy, and radio observations. The data, together with detailed spectral synthesis of the galaxy's integrated stellar population, show that G515 is a ~1 Gyr old postmerger, poststarburst galaxy. We detect no Balmer line emission in the galaxy, although there is a small amount of [N II] λλ6548, 6583 Å emission. The galaxy's H I mass has a 2 σ upper limit of 1.0 × 10⁹M_☉. IRAS detections in the 60 and 100 μm bands indicate a far-infrared luminosity of ~5.8 × 10¹⁰L_☉. A small amount (~3 mJy) of radio continuum flux, which appears to be variable, has been detected. The data suggest that G515 may have once been an ultraluminous infrared galaxy, and may harbor a weak, dust-obscured active nucleus.

We examine the properties of the diffuse hard X-ray emission in the classic starburst galaxy M82. We use new Chandra ACIS-S observations in combination with reprocessed archival Chandra ACIS-I and XMM-Newton observations. We find that E ~ 6.7 keV Fe Heα emission is present in the central |r| < 200 pc, |z| < 100 pc of M82 in all data sets, in addition to a possibly nonthermal X-ray continuum and marginally significant E = 6.4 keV Fe Kα line emission. No statistically significant Fe emission is found in the summed X-ray spectra of the pointlike X-ray sources or the ULXs in the two epochs of Chandra observation. The total nuclear region iron line fluxes in the 2004 April 21 XMM-Newton observation are consistent with those of the Chandra-derived diffuse component, but in the 2001 May 6 XMM-Newton observation they are significantly higher and also both E = 6.4 and 6.9 keV iron lines are detected. We attribute the excess iron line emission to the ULX in its high state. In general, the iron K-shell luminosity of M82 is dominated by the diffuse component. The total X-ray luminosity of the diffuse hard X-ray emission is L_{X,2-8 keV} ~ 4.4 × 10³⁹ ergs s^-1 in the E = 2-8 keV energy band, and the 6.7 keV iron line luminosity is L_{X,6.7 keV} ~ (1.1-1.7) × 10³⁸ ergs s^-1. The 6.7 keV iron line luminosity is consistent with that expected from the previously unobserved metal-enriched merged SN ejecta that is thought to drive the larger scale galactic superwind. The iron line luminosity implies a thermal pressure within the starburst region of P/k ~ 2 × 10⁷ K cm^-3, consistent with independent observational estimates of the starburst region pressure.

Emission spectra of hot accretion disks characteristic of advection-dominated accretion flow (ADAF) models are investigated for comparison with the brightest ultraluminous source, X-1, in the galaxy M82. If the spectral state of the source is similar to the low-luminosity hard state of stellar mass black holes in our Galaxy, a fit to the Chandra X-ray spectrum and constraints from the radio and infrared upper limits requires a black hole mass in the range of 9 × 10⁴-5 × 10⁵M_☉. Lower black hole masses (≲10⁴M_☉) are possible if M82 X-1 corresponds to the high-luminosity hard state of Galactic black hole X-ray binary sources. Both of these spectrally degenerate hot accretion disk solutions lead to an intermediate-mass black hole interpretation for M82 X-1. Since these solutions have different spectral variability with X-ray luminosity and predict different radio/infrared emission, they could be distinguished by future off-axis Chandra observations or simultaneous sensitive radio/infrared detections.

We examine the X-ray luminosity of galaxy groups in the CNOC2 survey at redshifts 0.1 < z < 0.6. Previous work examining the gravitational lensing signal of the CNOC2 groups has shown that they are likely to be genuine, gravitationally bound objects. Of the 21 groups in the field of view of the EPIC pn camera on XMM-Newton, not one was visible in over 100 ks of observation, even though three of them have velocity dispersions high enough that they would easily be visible if their luminosities scaled with their velocity dispersions in the same way as nearby groups' luminosities scale. We consider the possibility that this is due to the reported velocity dispersions being erroneously high and conclude that this is unlikely. We therefore find tentative evidence that groups at intermediate redshift are underluminous relative to their local cousins.

We present XMM-Newton, Chandra, and VLA observations of the USGC S152 group and its central elliptical NGC 3411. Imaging of the group X-ray halo suggests that it is relaxed with little apparent structure. We investigate the temperature and metal abundance structure of the group halo and find that while the abundance distribution is fairly typical, the temperature profile is highly unusual, showing a hot inner core surrounded by a cool shell of gas with a radius of ~20-40 kpc, at the center of the larger group halo. Spectral mapping confirms an irregular ring of gas ~0.15 keV cooler than its surroundings. We estimate the total mass, entropy, and cooling time profiles within ~200 kpc, and find that the cool shell contains ~9 × 10⁹M_☉ of gas. VLA observations at 1.4, 5, and 8 GHz reveal a relatively weak nuclear radio source, with a core radio luminosity L_R = 2.7 × 10³⁸ ergs s^-1 and a diffuse component extended on scales of a few arcseconds (or more). A lack of evidence for activity at optical or X-ray wavelengths supports the conclusion that the central black hole is currently in a quiescent state. We discuss possible mechanisms for the formation of temperature features observed in the halo, including a previous period of AGN activity, and settling of material stripped from the halo of one of the other group member galaxies.

The fine-structure lines of singly ([Ne II] 12.8 μm) and doubly ([Ne III] 15.6 μm) ionized neon are among the most prominent features in the mid-infrared spectra of star-forming regions and have the potential to be a powerful new indicator of the star formation rate in galaxies. Using a sample of star-forming galaxies with measurements of the fine-structure lines available from the literature, we show that the sum of the [Ne II] and [Ne III] luminosities obeys a tight, linear correlation with the total infrared luminosity over 5 orders of magnitude in luminosity. We discuss the formation of the lines and their relation with the Lyman continuum luminosity. A simple calibration between star formation rate and the [Ne II]+[Ne III] luminosity is presented.

We use deep J (1.25 μm) and K_s (2.15 μm) images of the Antennae (NGC 4038/4039) obtained with the Wide-field InfraRed Camera on the Palomar 200 inch (5 m) telescope, together with the Chandra X-ray source list of Zezas and coworkers to search for infrared counterparts to X-ray point sources. We establish an X-ray/IR astrometric frame tie with ~0.5'' rms residuals over a ~4.3' field. We find 13 "strong" IR counterparts brighter than K_s = 17.8 mag and <1.0'' from X-ray sources, and an additional 6 "possible" IR counterparts between 1.0'' and 1.5'' from X-ray sources. Based on a detailed study of the surface density of IR sources near the X-ray sources, we expect only ~2 of the "strong" counterparts and ~3 of the "possible" counterparts to be chance superpositions of unrelated objects. Comparing both strong and possible IR counterparts to our photometric study of ~220 IR clusters in the Antennae, we find with a >99.9% confidence level that IR counterparts to X-ray sources are ΔM_Ks ~ 1.2 mag more luminous than average non-X-ray clusters. We also note that the X-ray/IR matches are concentrated in the spiral arms and "overlap" regions of the Antennae. This implies that these X-ray sources lie in the most "super" of the Antennae's super star clusters, and thus trace the recent massive star formation history here. Based on the N_H inferred from the X-ray sources without IR counterparts, we determine that the absence of most of the "missing" IR counterparts is not due to extinction, but that these sources are intrinsically less luminous in the IR, implying that they trace a different (possibly older) stellar population. We find no clear correlation between X-ray luminosity classes and IR properties of the sources, although small-number statistics hamper this analysis.

We present chemical abundances for planetary nebulae and H II regions in the Local Group dwarf irregular galaxy NGC 6822 based on spectroscopy obtained at the Canada-France-Hawaii Telescope using the Multi-Object Spectrograph. From these and similar data compiled from the literature for planetary nebulae in the Magellanic Clouds, Sextans A, Sextans B, and Leo A, we consider the origin and evolution of the stellar progenitors of bright planetary nebulae in dwarf irregular galaxies. On average, the oxygen abundance observed in the bright planetary nebulae in these galaxies coincides with that measured in the ISM, indicating that, in general, the bright planetary nebulae in dwarf irregulars descend primarily, although not exclusively, from stars formed in the relatively recent past. We also find that the ratio of neon to oxygen abundances in these bright planetary nebulae is identical to that measured in the ISM, indicating that neither abundance is significantly altered as a result of the evolution of their stellar progenitors. We do find two planetary nebulae, that in Sextans A and S33 in NGC 6822, where oxygen appears to have been dredged up, but these are the exception rather than the rule. In fact, we find that even nitrogen is not always dredged up, so it appears that the dredge-up of oxygen is uncommon for the abundance range of the sample.

We use Sloan Digital Sky Survey Data Release 5 photometry and spectroscopy to study a tidal stream that extends over ~50° in the north Galactic cap. From the analysis of the path of the stream and the colors and magnitudes of its stars, the stream is ~20 kpc away at its nearest detection (the celestial equator). We detect a distance gradient: the stream is farther away from us at higher declination. The contents of the stream are made up from a predominantly old and metal-poor population that is similar to the globular clusters M13 and M92. The integrated absolute magnitude of the stream stars is estimated to be M_r ~ -7.5. There is tentative evidence for a velocity signature, with the stream moving at ~-40 km s^-1 at low declinations and ~+100 km s^-1 at high declinations. The stream lies on the same great circle as Complex A, a roughly linear association of H I high-velocity clouds stretching over ~30° on the sky, and as Ursa Major II, a recently discovered dwarf spheroidal galaxy. Lying close to the same great circle are a number of anomalous, young, and metal-poor globular clusters, including Palomar 1 and Ruprecht 106.

We report on observations of the stellar populations in 12 fields spanning the region between the Magellanic Clouds, made with the Mosaic II camera on the 4 m telescope at the Cerro-Tololo Inter-American Observatory. The two main goals of the observations are to characterize the young stellar population (which presumably formed in situ in the Bridge and therefore represents the nearest stellar population formed from tidal debris), and to search for an older stellar component (which would have been stripped from either Cloud as stars, by the same tidal forces that formed the gaseous Bridge). We determine the star formation history of the young inter-Cloud population, which provides a constraint on the timing of the gravitational interaction that formed the Bridge. We do not detect an older stellar population belonging to the Bridge in any of our fields, implying that the material that was stripped from the Clouds to form the Magellanic Bridge was very nearly a pure gas.

We have found Herbig Ae/Be star candidates in the western region of the Magellanic Bridge. Using the near-infrared camera SIRIUS and the 1.4 m telescope IRSF, we surveyed ~3.0° × 1.3° (24° ≲ α ≲ 36°, -75.0° ≲ δ ≲ -73.7°) in the J, H, and K_s bands. On the basis of colors and magnitudes, about 200 Herbig Ae/Be star candidates are selected. Considering the contaminations by miscellaneous sources, such as foreground stars and early-type dwarfs in the Magellanic Bridge, we estimate that about 80 (≈40%) of the candidates are likely to be Herbig Ae/Be stars. We also found one concentration of the candidates at the young star cluster NGC 796, strongly suggesting the existence of pre-main-sequence (PMS) stars in the Magellanic Bridge. This is the first detection of PMS star candidates in the Magellanic Bridge, and if they are genuine PMS stars, this could be direct evidence of recent star formation. However, the estimate of the number of Herbig Ae/Be stars depends on the fraction of classical Be stars, and thus a more precise determination of the Be star fraction or observations to differentiate between the Herbig Ae/Be stars and classical Be stars are required.

It is known that the carbon-enhanced, extremely metal-poor (CEMP) stars constitute a substantial proportion of the extremely metal-poor (EMP) stars of the Galactic halo, and a by far larger proportion than CH stars among Population II stars. We investigate their origin by taking into account an additional evolutionary path to the surface carbon enrichment, triggered by hydrogen engulfment by the helium flash convection, in EMP stars with [Fe/H] ≲ -2.5. This process is distinct from the third dredge-up operating in more metal-rich stars and in EMP stars. In binary systems of EMP stars, the secondary stars become CEMP stars through mass transfer from the low- and intermediate- mass primary stars that have developed the surface carbon enhancement. Our binary scenario can predict the variations in the abundances not only for carbon but also for nitrogen and s-process elements and can reasonably explain the observed properties such as the stellar distributions of the carbon abundances, the binary periods, and the evolutionary stages. Furthermore, from the observed frequencies of CEMP stars with and without s-process element enhancement, we demonstrate that the initial mass function of EMP stars needed gives the mean mass ~ 10 M_☉ under the reasonable assumptions for the distributions of orbital separations and mass ratios of the binary components. This also indicates that the currently observed EMP stars were exclusively born as the secondary members of binaries, making up ~10% of EMP binary systems, with mass ~ 10⁸M_☉ in total; in addition to CEMP stars with white dwarf companions, a significant fraction of them have experienced supernova explosions of their companions. We discuss the implications of the present results for the formation of the Galactic halo.

Currently there are two main techniques for independently determining the ages of stellar populations: main-sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. Open clusters provide the ideal environment for the calibration of these two clocks. Because current techniques to derive cluster ages from white dwarfs are observationally challenging, we discuss the feasibility of determining white dwarf ages from the brighter white dwarfs alone. This would eliminate the requirement of observing the coolest (i.e., faintest) white dwarfs. We discuss our method for testing this new idea, as well as the required photometric precision and prior constraints on metallicity, distance, and reddening. We employ a new Bayesian statistical technique to obtain and interpret results.

SN 1885 was a probable subluminous SN Ia that occurred in the bulge of the Andromeda galaxy, M31, at a projected location 16'' from the nucleus. Here we present and analyze Hubble Space Telescope images of the SN 1885 remnant seen in absorption against the M31 bulge via the resonance lines of Ca I, Ca II, Fe I, and Fe II. Viewed in Ca II H and K line absorption, the remnant appears as a nearly black circular spot with an outermost angular radius of 0.40'' ± 0.025'', implying a maximum linear radius of 1.52 ± 0.15 pc at M31's estimated distance of 785 ± 30 kpc and hence a 120 yr average expansion velocity of 12,400 ± 1400 km s^-1. The strongest Ca II absorption is organized in a broken ring structure with a radius of 0.2'' (=6000 km s^-1) with several apparent absorption "clumps" of an angular size around that of the image pixel scale of 0.05'' (=1500 km s^-1). Ca I and Fe I absorption structures appear similar except for a small Fe I absorption peak displaced 0.1'' off-center of the Ca II structure by a projected velocity of about 3000 km s^-1. Analyses of these images using off-center, delayed-detonation models suggest a low ⁵⁶Ni production similar to the subluminous SN Ia explosion of SN 1986G. The strongly lopsided images of Ca I and Fe I can be understood as resulting from an aspherical chemical distribution, with the best agreement found using an off-center model viewed from an inclination of ~60°. The images require a central region of no or little Ca but with iron group elements indicative for burning under sufficiently high densities for electron capture to take place, i.e., burning prior to a significant preexpansion of the WD.

Our imaging of the preplanetary nebula IRAS 19475+3119 (hereafter I19475) at 0.43 and 0.6 μm with HST reveals a quadrupolar nebula of size about 10.5'' × 4.7'', with two bipolar elongated lobes emanating from the center of the nebula. One of the bipolar lobes shows detailed point-symmetric structure with respect to the central star. A faint, surface brightness-limited, diffuse halo surrounds the lobes. Interferometric observations of the CO J = 1-0 line with OVRO at ~8'' resolution show that the bulk of the emission comes from an unresolved molecular envelope expanding at 15 km s^-1, resulting from the AGB progenitor's dense, slow wind. Weaker emission is seen from a fast bipolar outflow oriented along the longer and more tenuous pair of the sets of lobes. Optical spectroscopy reveals a complex Hα profile with a broad photospheric absorption feature and a narrow inverse P Cygni shaped core; comparison with previous data shows that the core profile shape varies dramatically with time. We find an unresolved source of millimeter-wave continuum emission in I19475, which together with previous submillimeter continuum measurements, implies a very substantial mass (roughly a few times 0.01 M_☉) of large (radius ≳1 mm), cold (~30 K) dust grains in I19475. Combining our estimates of the circumstellar mass with the typical mass of a post-AGB star, we find that the main-sequence progenitor of I19475's central star had a mass ≳2.5 M_☉. We discuss the formation of I19475's quadrupolar nebula in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass ejecta as AGB stars evolve into planetary nebulae.

We perform three-dimensional (3D) compressible MHD simulations over many dynamical times for an extended range of sonic and Alfvén Mach numbers and analyze the statistics of 3D density and 2D column density, which include probability distribution functions, spectra, skewness, kurtosis, She-Lévêque exponents, and genus. In order to establish the relation between the statistics of the observables, i.e., column densities, and the underlying 3D statistics of density, we analyze the effects of cloud boundaries. We define the parameter space for 3D measures to be recovered from column densities. In addition, we show that for subsonic turbulence the spectra of density fluctuations are consistent with k^-7/3 in the case of a strong magnetic field and k^-5/3 in the case of a weak magnetic field. For supersonic turbulence we confirm the earlier findings of the shallow spectra of density and Kolmogorov spectra of the logarithm of density. We find that the intermittencies of the density and velocity are very different.

We have used archival far-ultraviolet spectra from observations made by HST STIS and FUSE to determine the column densities and rotational excitation temperatures for carbon monoxide and molecular hydrogen, respectively, along 23 sight lines to Galactic O and B stars. The reddening values range from E(B - V) = 0.07 to 0.62, sampling the diffuse to translucent interstellar medium (ISM). We find that the H₂ column densities range from 5 × 10¹⁸ to 8 × 10²⁰ cm^-2 and the CO from upper limits around 2 × 10¹² cm^-2 to detections as high as 1.4 × 10¹⁶ cm^-2. CO increases with increasing H₂, roughly following a power law of factor ~2. The CO/H₂ column density ratio is thus not constant, ranging from 10^-7 to 10^-5, with a mean value of 3 × 10^-6. The sample segregates into "diffuse" and "translucent" regimes, the former with molecular fraction ≲0.25 and A_V/d < 1 mag kpc^-1. The mean CO/H₂ for these two regimes are 3.6 × 10^-7 and 9.3 × 10^-6, respectively, significantly lower than the canonical dark cloud value of 10^-4. Six sight lines show the isotopic variant ¹³CO, and the isotopic ratio we observe (~50-70) is consistent with, if perhaps a little below, the average ¹²C/¹³C for the ISM at large. The average H₂ rotational excitation temperature is 74 ± 24 K, agreeing well with previous studies, and the average CO temperature is 4.1 K, with some sight lines showing temperatures as high as 6.4 K. The higher excitation CO is observed with higher column densities, consistent with the effects of photon trapping in clouds with densities in the 20-100 cm^-3 range. We discuss the implications for the structure of the diffuse/translucent regimes of the ISM and the estimation of molecular mass in galaxies.

The ¹³C substitutions of the molecule HC₇N were observed in TMC-1 using the J = 12-11, J = 13-12 rotational transitions in the frequency range 12.4-13.6 GHz. We present the first detection of the ¹³C isotopic species of HC₇N in the interstellar medium, based on the average of a number of weak rotational transitions. This paper describes the calibration and data-averaging process that is also used in a search for large cyanopolyyne molecules in TMC-1 using the 100 m Robert C. Byrd Green Bank Telescope (GBT). The capabilities of the GBT 11-15 GHz observing system are described, along with a discussion of numerical methods for averaging observations of a number of weak spectral lines to detect new interstellar molecules.

We present a new model-independent method of comparison of NIR visibility data of YSOs. The method is based on scaling the measured baseline with the YSO's distance and luminosity, which removes the dependence of visibility on these two variables. We use this method to compare all available NIR visibility data and demonstrate that it distinguishes YSOs of luminosity L_⋆ ≲ 10³L_☉ (low L) from YSOs of L_⋆ ≳ 10³L_☉ (high L). This confirms earlier suggestions, based on fits of image models to the visibility data, for the difference between the NIR sizes of these two luminosity groups. When plotted against the "scaled" baseline, the visibility creates the following data clusters: low-L Herbig Ae/Be stars, T Tauri stars, and high-L Herbig Be stars. We model the shape and size of clusters with different image models and find that low-L Herbig stars are best explained by the uniform brightness ring and the halo model, T Tauri stars with the halo model, and high-L Herbig stars with the accretion disk model. However, the plausibility of each model is not well established. Therefore, we try to build a descriptive model of the circumstellar environment consistent with various observed properties of YSOs. We argue that low-L YSOs have optically thick disks with the optically thin inner dust sublimation cavity and an optically thin dusty outflow above the inner disk regions. High-L YSOs have optically thick accretion disks with high accretion rates enabling gas to dominate the NIR emission over dust. Although observations would favor such a description of YSOs, the required dust distribution is not supported by our current understanding of dust dynamics.

Kinematical analysis of spectroscopically identified pre-main-sequence stars associated with the Lupus dark cloud reveals a streamlike motion of low internal velocity dispersion (≤1.3 km s^-1). A statistically significant mismatch between the convergent point radial velocity and the spectroscopic radial velocity from the literature indicates a moderate degree of expansion. The rate of expansion is too low to account for the present extent of the association if one assumes that the spatially dispersed population was formed in the dense molecular cores observed today. Therefore, it is unlikely that the outlying weak-lined T Tauri members were born in the same star-forming cores as the more compactly located classical T Tauri stars, despite the kinematic integrity of the association. Distances inferred from the classical moving-cluster method show a large depth of the association (~80 pc) along the line of sight. A color-magnitude diagram of the association in the near-IR colors corrected for the distribution of distances shows a clear gap separating the older (5-27 Myr) and the younger (~1 Myr) generations of stars. Half of the identified 1 Myr old stars lie in the tight group of mostly classical T Tauri stars associated with the Lupus 3 dark filament. This nest of very young stars appears to be 25 pc farther from the Sun than the center of the greater Lupus association.

We present Spitzer IRAC and IRS observations of the dark cloud L1287. The mid-infrared (MIR) IRAC images show deeply embedded infrared sources in the vicinity of the FU Orionis objects RNO 1B and RNO 1C, suggesting their association with a small young stellar cluster. We resolve for the first time the MIR point source associated with IRAS 00338+6312, which is a deeply embedded intermediate-mass protostar driving a known molecular outflow. The IRAC colors of all the objects are consistent with those of young stars ranging from deeply embedded Class 0/I sources to Class II objects, some of which appear to be locally reddened. The two IRS spectra show strong absorption bands due to ices and dust particles, confirming that the circumstellar environment around RNO 1B/1C has a high optical depth. Additional hydrogen emission lines from pure rotational transitions are superposed on the spectra. Given the outflow direction, we attribute these emission lines to shocked gas in the molecular outflow powered by IRAS 00338+6312. The derived shock temperatures are in agreement with predictions for high-velocity C-type shocks.

We present single-dish and interferometric millimeter line observations of the HH 111 outflow and its driving source. The physical conditions of the core have been determined from the emission of the millimeter line of CO and its isotopomers and CS with the IRAM 30 m telescope, and the CO J = 7 → 6 line with the Caltech Submillimeter Observatory. The emission reveals a small condensation of cold (T = 20-25 K) and dense gas [n(H₂) = 3 × 10⁵ cm^-3]. The outflow has been mapped with the IRAM Plateau de Bure interferometer (PdBI). The cold gas is distributed in a hollow cylinder surrounding the optical jet. The formation of this cavity and its kinematics are well accounted for in the frame of outflow gas entrainment by jet bow shocks. Evidence of gas acceleration is found along the cavity walls, correlated with the presence of optical bow shocks. The separation of the inner walls reaches 8''-10'', which matches the transverse size of the wings in the bow shock. CSO observations of the J = 7 → 6 line show evidence of a high-velocity and hot gas component (T = 300-1000 K) with a low filling factor. This emission probably arises from shocked gas in the jet. Observations of the ³P₂-³P₁ [C I] line are consistent with C-type nondissociative shocks. Mapping of the high-velocity molecular bullets B1-B3, located beyond the optical jet, reveals small structures of 3'' × 7'' flattened perpendicular to the flow direction. They are made of cold (T ~ 30 K), moderate density gas [n(H₂) = (0.5-1.0) × 10⁴ cm^-3], expanding into the low-density surrounding medium. Their properties are consistent with their being shocked gas knots resulting from past time-variable ejections in the jet.

We obtained 98 R-band and 18 B, r', i' images of the optical afterglow of GRB 060526 (z = 3.21) with the MDM 1.3 m, 2.4 m, and the PROMPT telescopes at CTIO over the five nights following the burst trigger. Combining these data with other optical observations reported in GCN and the Swift XRT observations, we compare the optical and X-ray afterglow light curves of GRB 060526. Both the optical and X-ray afterglow light curves show rich features, such as flares and breaks. The densely sampled optical observations provide very good coverage at T > 10⁴ s. We observed a break at 2.4 × 10⁵ s in the optical afterglow light curve. Compared with the X-ray afterglow light curve, the break is consistent with an achromatic break supporting the beaming models of GRBs. However, the prebreak and postbreak temporal decay slopes are difficult to explain in simple afterglow models. We estimated a jet angle of θ_j ~ 7° and a prompt emission size of R_prompt ~ 2 × 10¹⁴ cm. In addition, we detected several optical flares with amplitudes of Δm ~ 0.2, 0.6, and 0.2 mag. The X-ray afterglows detected by Swift have shown complicated decay patterns. Recently, many well-sampled optical afterglows also show decays with flares and multiple breaks. GRB 060526 provides an additional case of such a complex, well-observed optical afterglow. The accumulated well-sampled afterglows indicate that most of the optical afterglows are complex.

We report the detection of pulsations from two accreting transient high-mass X-ray binaries (HMXBs) at low X-ray luminosities (≈1-4 × 10³⁴ ergs s^-1). While one (4U 1145-619) has been detected pulsing previously at a lower luminosity, the second (1A 1118-615) has not, making it the third such transient HMXB from which pulsations are detected at low luminosity. The pulsars exhibit broadband rms variability (22.3% ± 0.1% and 9.2% ± 0.1%, respectively). While the present observations do not permit measurement of a spin frequency derivative, spin-down is implied in comparison with previous Compton Gamma Ray Observatory/BATSE observations. If spin-down occurred at the presently observed X-ray luminosity of 4U 1145-619, the required mass accretion rate is insufficient to produce the observed X-ray luminosity from a shock at the magnetosphere, and only a fraction of the mass accretion makes its way to the neutron star surface, with most of the mass leaving the system, carrying away angular momentum to affect spin-down.

We report observations of the recurrent nova RS Oph using long-baseline near-IR interferometry. We are able to resolve emission from the nova for several weeks after the 2006 February outburst. The near-IR source initially expands to a size of ~5 mas. However, beginning around day 10, the IR source appears to begin to shrink, reaching ~2 mas by day 100. We combine our measured angular diameters with previously available interferometric and photometric data to derive an emission measure for the source, and hence are able to determine the mass-loss rate of the nova in the days following the outburst.

We present the results of high-resolution spectroscopy of the prototype Polar AM Herculis observed with Chandra High Energy Transmission Grating . The X-ray spectrum contains hydrogen-like and helium-like lines of Fe, S, Si, Mg, Ne, and O, with several Fe L-shell emission lines. The forbidden lines in the spectrum are generally weak, whereas the hydrogen-like lines are stronger suggesting that emission from a multitemperature, collisionally ionized plasma dominates. The helium-like line flux ratios yield a plasma temperature of 2 MK and a plasma density 1-9 × 10¹² cm^-3, whereas the line flux ratio of Fe XXVI to Fe XXV gives an ionization temperature of 12.4 keV. We present the differential emission measure distribution of AM Her, whose shape is consistent with the volume emission measure obtained by a multitemperature APEC model. The multitemperature plasma model fit to the average X-ray spectrum indicates the mass of the white dwarf to be ~1.15 M_☉. From phase-resolved spectroscopy, we find the line centers of Mg XII, S XVI, resonance line of Fe XXV, and Fe XXVI emission modulated by a few hundred to 1000 km s^-1 from the theoretically expected values, indicating bulk motion of ionized matter in the accretion column of AM Her. The observed velocities of Fe XXVI ions are close to the expected shock velocity for a 0.6 M_☉ white dwarf. The observed velocity modulation is consistent with that expected from a single pole accreting binary system.

We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H] = -3.9. From a high-resolution, high-S/N Subaru HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements (CEMP-no). Several potential enrichment scenarios are presented. The nondetection of neutron-capture elements including Sr, Ba, and Pb suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single faint SN is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population III object and a hypernova. These scenarios provide important information on the C production in the early universe and on the formation of C-rich stars in the early Galaxy.

We present radio observations of eight ultracool dwarfs with a narrow spectral type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8 binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system detected in radio wavelengths and its trigonometric parallax π = 67.6 mas, recently measured by Gatewood and coworkers, makes it the furthest ultracool system detected by the Very Large Array to date, and the most radio luminous outside of obvious flaring activity or variability. With a separation of only 1.8 AU, masses of the components of LP 349-25 can be measured precisely without any theoretical assumptions, allowing us to clarify their fully convective status and hence the kind of magnetic dynamo in these components, which may play an important role in explaining our detection of radio emissions from these objects. This also makes LP 349-25 an excellent target for further studies with better constraints on the correlations between X-ray, and radio emission and stellar parameters such as mass, age, temperature, and luminosity in ultracool dwarfs.

We report the discovery of the wide L1.5+L4.5 binary 2MASS J15200224-4422419AB, identified during spectroscopic follow-up of high proper motion sources selected from the Two Micron All Sky Survey. This source was independently identified by Kendall et al. in the SuperCOSMOS Sky Survey. Resolved JHK photometry and low-resolution near-infrared spectroscopy demonstrate that this system is composed of two well-separated (1.174'' ± 0.016'') L dwarfs. Component classifications are derived using both spectral ratios and comparison to the near-infrared spectra of previously classified field L dwarfs. Physical association for the pair is deduced from the large common proper motion of the components (μ = 0.73'' ± 0.03'' yr^-1) and their similar spectrophotometric distances (19 ± 2 pc). The projected separation of the binary, 22 ± 2 AU, is consistent with maximum separation/total system-mass trends for very low mass binaries. The 2MASS J1520-4422 system exhibits both large tangential (66 ± 7 km s^-1) and radial velocities (-70 ± 18 km s^-1), and its motion in the local standard of rest suggests that it is an old member of the Galactic disk population. This system joins a growing list of well-separated (>0.5''), very low mass binaries, and is an excellent target for resolved optical spectroscopy to constrain its age, as well as trace activity/rotation trends near the hydrogen-burning limit.

In this paper a simple model for the steady state evolution of debris disks due to collisions is developed and confronted with the properties of the emerging population of seven Sun-like stars that have hot dust at <10 AU. The model shows that there is a maximum possible disk mass at a given age, since more massive primordial disks process their mass faster. The corresponding maximum dust luminosity is f_max = 0.16 × 10^-3r^7/3t, where r is disk radius in AU and t_age is system age in Myr. The majority (4/7) of the hot disks exceed this limit by ≫1000 and so cannot be the products of massive asteroid belts; rather, the following systems must be undergoing transient events characterized by an unusually high dust content near the star: η Corvi, HD 69830, HD 72905, and BD +20 307. It is also shown that the hot dust cannot originate in a recent collision in an asteroid belt, since there is also a maximum rate at which collisions of sufficient magnitude to reproduce a given dust luminosity can occur. The planetesimal belt feeding the dust in these systems must be located farther from the star than the dust, typically at ≫2 AU. Other notable properties of the four hot dust systems are as follows: two also have a planetesimal belt at >10 AU (η Corvi and HD 72905); one has three Neptune mass planets at <1 AU (HD 69830); all exhibit strong mid-IR silicate features. We consider the most likely origin for this transient dust to be a dynamical instability that scattered planetesimals inward from a more distant planetesimal belt in an event akin to the late heavy bombardment in our own system, the dust being released from such planetesimals in collisions and sublimation.

We have used the infrared mineralogical model derived from the Spitzer IRS observations of the Deep Impact experiment to study the nature of the dust in the debris found around the K0 V star HD 69830. Using a robust approach to determine the bulk average mineralogical composition of the dust, we show it to be substantially different from that found for comets 9P/Tempel 1 and C/Hale-Bopp 1995 O1 or for the comet-dominated YSO HD 100546. Lacking in carbonaceous and ferrous materials but including small icy grains, the composition of the HD 69830 dust most closely resembles that of a disrupted P- or D-type asteroid. The amount of mass responsible for the observed emission is the equivalent of a 30 km radius, 2500 kg m^-3 sphere, while the radiative temperature of the dust implies that the bulk of the observed material is at ~1.0 AU from the central source, coincident with the 2 : 1 and 5 : 2 mean motion resonances of the outermost of three Neptune-sized planets detected by Lovis and coworkers. In our solar system, P- and D-type asteroids are both large and numerous in the outer main belt and near Jupiter (e.g., the Hildas and Trojans) and have undergone major disruptive events to produce debris disk-like structures (cf. the Karin and Veritas families 5-8 Myr ago). The short-lived nature of the small and icy dust implies that the disruption occurred within the last year, or that replenishment due to ongoing collisional fragmentation is occurring.

Planetesimal accretion during planet formation is usually treated as collisionless. Such accretion from a uniform and dynamically cold disk predicts protoplanets with slow retrograde rotation. However, if the building blocks of protoplanets, planetesimals, are small, of the order of a meter in size, then they are likely to collide within the protoplanet's sphere of gravitational influence, creating a prograde accretion disk around the protoplanet. The accretion of such a disk results in the formation of protoplanets spinning in the prograde sense with the maximal spin rate allowed before centrifugal forces break them apart. As a result of semicollisional accretion, the final spin of a planet after giant impacts is not completely random, but is biased toward prograde rotation. The eventual accretion of the remaining planetesimals in the post-giant-impact phase might again be in the semicollisional regime and delivers a significant amount of additional prograde angular momentum to the terrestrial planets. We suggest that in our solar system, semicollisional accretion gave rise to the preference for prograde rotation observed in the terrestrial planets and perhaps the largest asteroids.

We have developed a characterization of the geological evolution of the Earth's atmosphere and surface in order to model the observable spectra of an Earth-like planet through its geological history. These calculations are designed to guide the interpretation of an observed spectrum of such a planet by future instruments that will characterize exoplanets. Our models focus on planetary environmental characteristics whose resultant spectral features can be used to imply habitability or the presence of life. These features are generated by H₂O, CO₂, CH₄, O₂, O₃, N₂O, and vegetation-like surface albedos. We chose six geological epochs to characterize. These epochs exhibit a wide range in abundance for these molecules, ranging from a CO₂-rich early atmosphere, to a CO₂/CH₄-rich atmosphere around 2 billion years ago, to a present-day atmosphere. We analyzed the spectra to quantify the strength of each important spectral feature in both the visible and thermal infrared spectral regions, and the resolutions required to optimally detect the features for each epoch. We find a wide range of spectral resolutions required for observing the different features. For example, H₂O and O₃ can be observed with relatively low resolution, while O₂ and N₂O require higher resolution. We also find that the inclusion of clouds in our models significantly affects both the strengths of all spectral features and the resolutions required to observe all these.

I present detailed analysis of the near-infrared spectrum of HD 3651B, a faint, comoving wide companion to the nearby planet-hosting star HD 3651. These data confirm the companion as a brown dwarf with spectral type T8, consistent with the analysis of Luhman et al. Application of the semi-empirical technique of Burgasser, Burrows, & Kirkpatrick indicates that HD 3651B has T_eff = 790 ± 30 K and log g = 5.0 ± 0.3 for a metallicity of [M/H] = 0.12 ± 0.04, consistent with a mass M = 0.033 ± 0.013 M_☉ and an age of 0.7-4.7 Gyr. The surface gravity, mass, and age estimates of this source are all highly sensitive to the assumed metallicity; however, a supersolar metallicity is deduced by direct comparison of spectral models to the observed absolute fluxes. The age of HD 3651B is somewhat better constrained than that of the primary, with estimates for the latter ranging over ~2 Gyr to >12 Gyr. As a widely orbiting massive object to a known planetary system that could potentially harbor terrestrial planets in its habitable zone, HD 3651B may play the role of Nemesis in this system.

We report on Monte Carlo simulations of solar energetic particle (SEP) acceleration at quasi-parallel coronal shocks under the influence of self-generated Alfvén waves. The results indicate that the accelerated particles amplify ambient Alfvén waves efficiently and that the solution close to the shock can be qualitatively described with the results from quasi-steady theories of diffusive shock acceleration, provided that the acceleration and injection parameters do not change rapidly. The escape of the first particles to the interplanetary medium occurs before the waves have grown appreciably to trap the particles in the vicinity of the shock wave. The escape process is well described by the analytical model developed by Vainio, at least for the promptly escaping component. In addition to the compression ratio and speed of the shock wave, the rate of injection of low-energy particles to the acceleration process is a key factor for the acceleration efficiency of shocks that are driven by coronal mass ejection. Quasi-parallel coronal shocks seem to be capable of accelerating suprathermal protons up to 100 MeV and beyond after some number of minutes. Extrapolations of our simulation results indicate, however, that the wave intensities may reach nonlinear values before acceleration to GeV energies occurs in the corona. This may mean that the quasi-linear approach has to be replaced by a more general theory to describe particle acceleration at quasi-parallel coronal shocks in the largest SEP events.

A test-particle approach is used to study the collisionless response of protons to cold plasma fast Alfvén waves propagating in a nonuniform magnetic field: specifically, a two-dimensional X-point field. The field perturbations associated with the waves, which are assumed to be azimuthally symmetric and invariant in the direction orthogonal to the X-point plane, are exact solutions of the linearized ideal magnetohydrodynamic (MHD) equations. The protons are initially Maxwellian, at temperatures that are consistent with the cold plasma approximation. Two kinds of wave solution are invoked: global perturbations, with inward- and outward-propagating components; and localized purely inward-propagating waves, the wave electric field E having a preferred direction. In both cases the protons are effectively heated in the direction parallel to the magnetic field, although the parallel velocity distribution is generally non-Maxwellian and some protons are accelerated to highly suprathermal energies. This heating and acceleration can be attributed to the fact that protons undergoing E × B drifts due to the presence of the wave are subject to a force in the direction parallel to B. The localized wave solution produces more effective proton heating than the global solution, and successive wave pulses have a synergistic effect. This process, which could play a role in both solar coronal heating and late-phase heating in solar flares, is effective for all ion species, but it has a negligible direct effect on electrons. However, both electrons and heavy ions would be expected to acquire a temperature comparable to that of the protons on collisional timescales.

We investigate the plasma dynamics (outflow speed and turbulence) inside polar plumes. We compare line profiles (mainly of O VI) observed by the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on SOHO at the minimum of solar cycle 22-23 with model calculations. We consider Maxwellian velocity distributions with different widths in plume and interplume regions. Electron densities are assumed to be enhanced in plumes and to approach interplume values with increasing height. Different combinations of the outflow and turbulence velocity in the plume regions are considered. We compute line profiles and total intensities of the H I Lyα and the O VI doublets. The observed profile shapes and intensities are reproduced best by a small solar wind speed at low altitudes in plumes that increases with height to reach ambient interplume values above roughly 3-4 R_☉, combined with a similar variation of the width of the velocity distribution of the scattering atoms/ions. We also find that plumes very close to the pole give narrow profiles at heights above 2.5 R_☉, which are not observed. This suggests a tendency for plumes to be located away from the pole. We find that the inclusion of plumes in the model computations provides an improved correspondence with the observations and confirms previous results showing that published UVCS observations in polar coronal holes can be roughly reproduced without the need for large temperature anisotropy. The latitude distributions of plumes and magnetic flux distributions are studied by analyzing data from different instruments on SOHO and with SOLIS.

The Gnevyshev-Ohl rule refers to a pattern of alternating higher and lower than average solar cycle amplitudes observed in the sunspot number record. In this paper, we show that such a pattern arises naturally in Babcock-Leighton models of the solar cycle as a consequence of the long time delay built into the dynamo regenerative loop. This is investigated using a simple but well-validated iterative map formulation, as well as a seasoned two-dimensional axisymmetric kinematic dynamo model. The good agreement between the results obtained via these two very different modeling approaches offers confidence that Gnevyshev-Ohl-like patterns of cycle amplitude fluctuations are a robust feature of this class of solar cycle models.

Both induced Compton scattering and induced Raman scattering strongly limit the observability of the extremely bright (≫10²¹ K), prompt coherent radio emission recently predicted to emanate from gamma-ray bursts (GRBs). Induced Compton scattering is the main limiting factor when the region around the progenitor is not dense but when one still considers the scattering effect of a tenuous circumburst ISM. For a medium of density 0.01n_0.01 cm^-3 and a path length L_kpc kpc and emission that is roughly isotropic in its rest frame, the brightness temperature is limited to <3 × 10¹⁸ΓnL K, where 100Γ₁₀₀ is the Lorentz factor of the frame in which the emission occurs. Thus, for a burst at distance D the predicted emission is only visible if the jet is ultrarelativistic, with Γ ≳ 10³(D/100 Mpc), or if the intrinsic opening angle of the emission is extremely small. Thus, the presence or absence of such radio emission provides an excellent constraint on the Lorentz factor of the GRB outflow during the very early stages of its outburst. Induced Raman scattering imposes an even more stringent limit independent of the emission opening angle, but only effective if GRB emission must propagate through a dense progenitor wind within ~10¹⁵ cm from the blast center.

Optical spectroscopy and photometry of SN 2006aj have been performed with the Subaru telescope at t > 200 days after GRB 060218, the X-ray flash with which it was associated. Strong nebular emission lines with an expansion velocity of v ~ 7300 km s^-1 were detected. The peaked but relatively broad [O I] λλ6300, 6363 suggests the existence of ~2 M_☉ of materials in which ~1.3 M_☉ is oxygen. The core might be produced by a mildly asymmetric explosion. The spectra are unique among SNe Ic in (1) the absence of [Ca II] λλ7291, 7324 emission and (2) a strong emission feature at ~7400 Å, which requires ~0.05 M_☉ of newly synthesized ⁵⁸Ni. Such a large amount of stable neutron-rich Ni strongly indicates the formation of a neutron star. The progenitor and the explosion energy are constrained to 18 M_☉ ≲ M_ms ≲ 22 M_☉ and E ~ (1-3) × 10⁵¹ ergs, respectively.

We derive the kinetic luminosity function for flat-spectrum radio jets, using the empirical and theoretical scaling relation between jet power and radio core luminosity. The normalization for this relation is derived from a sample of flat-spectrum cores in galaxy clusters with jet-driven X-ray cavities. The total integrated jet power at z = 0 is W_tot ≈ 3 × 10⁴⁰ ergs s^-1 Mpc^-3. By integrating W_tot over redshift, we determine the total energy density deposited by jets as e_tot ≈ 2 × 10⁵⁸ ergs Mpc^-3. Both W_tot and e_tot are dominated by low-luminosity sources. Comparing e_tot to the local black hole mass density ρ_BH gives an average jet production efficiency of _jet = e_jet/ρ_BHc² ≈ 3%. Since black hole mass is accreted mainly during high-luminosity states, _jet is likely much higher during low-luminosity states.

We report the identification of 2MASX J032441.19+341045.9 (hereafter 2MASX J0324+3410) with an appealing object that shows the dual properties of both a narrow-line Seyfert 1 galaxy (NLS1) and a blazar. Its optical spectrum, which has a Hβ line width of about 1600 km s^-1 (FWHM), an [O III]-to-Hβ line ratio of ≃0.12, and strong Fe II emission, clearly fulfills the conventional definition of NLS1s. On the other hand, 2MASX J0324+3410 also exhibits some behavior that is characteristic of blazars, including a flat radio spectrum above 1 GHz, a compact core plus a one-sided jet structure on milliarcsecond scale at 8.4 GHz, highly variable fluxes in the radio, optical, and X-ray bands, and a possible detection of TeV γ-ray emission. On its optical image, obtained with the HST WFPC2, the active nucleus is displaced from the center of the host galaxy, which exhibits an apparent one-armed spiral structure extended to 16 kpc. The remarkable hybrid behavior of this object presents a challenge to current models of NLS1s and γ-ray blazars.

We present modified Newtonian dynamics (MOND) analysis for several of the lowest mass disk galaxies currently amenable to such analysis, with (baryonic) masses below 4 × 10⁸M_☉. The agreement is good, extending the validity of MOND and its predicted mass velocity relation, to such low masses.

Constraining the astrophysical nature of ultraluminous X-ray (ULX) sources, which have X-ray luminosities exceeding 10³⁹ ergs s^-1, has been elusive due to the optical faintness of any counterparts. With high spectral resolution observations in the ~10-30 μm wavelength range we have conducted an experiment to study six ULX sources in the NGC 4485/4490 galaxy pair. We have found that five of the six ULXs, based on mid-infrared spectral diagnostics, show the characteristic higher ionization features that are found in AGNs. The sixth source, ULX-1, is consistent with being a supernova remnant. The chief infrared spectral diagnostics used are the ratios of [S III]/[Si II] versus [Ne III]/[Ne II]. In two instances fits to the continuum and polycyclic aromatic hydrocarbon (PAH) features also indicate higher dust temperatures, which are characteristic of accreting sources. Overall, however, we find that the continuum is dominated by stellar processes, and the best diagnostic features are the emission lines. High spectral resolution studies in the mid-infrared thus appear to show great promise for determining the astrophysical nature of ULXs.

After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a luminous blue variable only years after its eruption and shows that the dominant source of the X-rays is not associated with the ejecta.

We are undertaking a large-scale radial velocity survey of the Galactic bulge that uses M giant stars selected from the Two Micron All Sky Survey catalog as targets for the Cerro Tololo Inter-American Observatory 4 m Hydra multiobject spectrograph. The aim of this survey is to test dynamical models of the bulge and to quantify the importance, if any, of cold stellar streams in the bulge and its vicinity. Here we report on the kinematics of a strip of fields at -10° < l < +10° and b = -4°. We construct a longitude-velocity plot for the bulge stars and the model data and find that, contrary to previous studies, the bulge does not rotate as a solid body. From -5° < l < +5° the rotation curve has a slope of roughly 100 km s^-1 kpc^-1 and flattens considerably at greater l, reaching a maximum rotation of 45 km s^-1. We compare our rotation curve and velocity dispersion profile to both the self-consistent model of Zhao and to N-body models; neither fits both our observed rotation curve and velocity dispersion profile. The high precision of our radial velocities (~3 km s^-1) yields an unexpected result: hints of cold kinematic features are seen in a number of the line-of-sight velocity distributions.

The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and radiation in the Galaxy is one of the few probes available to study the origin of the cosmic rays. Data from the Milagro gamma-ray observatory—a water Cerenkov detector that continuously views ~2 sr of the overhead sky—shows that the brightest extended region in the entire northern sky is the Cygnus region of the Galactic plane. The TeV image of the Cygnus region contains at least one new source, MGRO J2019+37, which is 10.9 σ above the isotropic background, as well as correlations with the matter density in the region. However, the gamma-ray flux from the Cygnus region (after excluding MGRO J2019+37) as measured at ~12 TeV exceeds that predicted from a model of cosmic-ray production and propagation. This observation indicates the existence of either hard-spectrum cosmic-ray sources and/or unresolved sources of TeV gamma rays in the region.

Networks of reactions on dust-grain surfaces play a crucial role in the chemistry of interstellar clouds, leading to the formation of molecular hydrogen in diffuse clouds as well as various organic molecules in dense molecular clouds. Due to the submicron size of the grains and the low flux, the population of reactive species per grain may be very small and strongly fluctuating. Under these conditions rate equations fail, and the simulation of surface-reaction networks requires stochastic methods such as the master equation. However, the master equation becomes infeasible for complex networks because the number of equations proliferates exponentially. Here we introduce a method based on moment equations for the simulation of reaction networks on small grains. The number of equations is reduced to just one equation per reactive species and one equation per reaction. Nevertheless, the method provides accurate results, which are in excellent agreement with the master equation. The method is demonstrated for the methanol network that has been recently shown to be of crucial importance.

Several indirect evidences indicate a magnetic origin for the nonthermal width of spectral lines observed toward molecular clouds. In this Letter, I suggest that the origin of the nonthermal width of carbon recombination lines (CRLs) observed from photodissociation regions (PDRs) near ultracompact H II regions is magnetic and that the magnitude of the line width is an estimate of the Alfvén speed. The magnetic field strengths estimated based on this suggestion compare well with those measured toward molecular clouds with densities similar to PDR densities. I conclude that multifrequency CRL observations have the potential to form a new tool to determine the field strength near star-forming regions.

We have mapped [Ne II] (12.8 μm) and [S IV] (10.5 μm) emission from W51 IRS 2 with TEXES on Gemini North, and we compare these data to VLA free-free observations and VLT near-infrared images. With 0.5'' spatial and 4 km s^-1 spectral resolution, we are able to separate the ionized gas into several components: an extended H II region on the front surface of the molecular cloud, several embedded compact H II regions, and a streamer of high-velocity gas. We interpret the high-velocity streamer as a precessing or fanlike jet, which has emerged from the molecular cloud into an OB star cluster where it is being ionized.

Recent investigations on the delay time of Type Ia supernovae have set useful constraints on the progenitors of Type Ia supernovae. Here we have calculated the evolution of close binaries consisting of a white dwarf and a main-sequence or subgiant companion. We assume that, once Roche lobe overflow occurs, a small fraction of the lost mass from the system forms a circumbinary disk, which extracts the orbital angular momentum from the system through tidal torques. Our calculations indicate that the existence of a circumbinary disk can enhance the mass transfer rate and cause secular orbital shrinkage. The white dwarf can grow in mass efficiently to trigger Type Ia supernovae even with relatively low mass (≲2 M_☉) donor stars. Thus, this scenario suggests a new possible evolutionary channel to those Type Ia supernovae with long delay times ~1-3 Gyr.

Using the Submillimeter Array (SMA) we have imaged for the first time the 321.226 GHz, 10₂₉-9₃₆ ortho-H₂O maser emission. This is also the first detection of this line in the Cepheus A high-mass star-forming region. The 22.235 GHz, 6₁₆-5₂₃ water masers were also observed with the Very Large Array 43 days following the SMA observations. Three of the nine detected submillimeter maser spots are associated with the centimeter masers spatially as well as kinematically, while there are 36 22 GHz maser spots without corresponding submillimeter masers. In the HW2 source, both the 321 and 22 GHz masers occur within the region of ~1'', which includes the disk-jet system, but the position angles of the roughly linear structures traced by the masers indicate that the 321 GHz masers are along the jet while the 22 GHz masers are perpendicular to it. We interpret the submillimeter masers in Cepheus A to be tracing significantly hotter regions (600-2000 K) than the centimeter masers.

The observed mass function for all known extrasolar giant planets (EGPs) varies approximately as M^-1 for mass M between ~0.2 Jupiter masses (M_J) and ~5 M_J. In order to study evaporation effects for highly irradiated EGPs in this mass range, we have constructed an observational mass function for a subset of EGPs in the same mass range but with orbital radii <0.07 AU. Surprisingly, the mass function for such highly irradiated EGPs agrees quantitatively with the M^-1 law, implying that the mass function for EGPs is preserved despite migration to small orbital radii. Unless there is a remarkable compensation of mass-dependent orbital migration for mass-dependent evaporation, this result places a constraint on orbital migration models and rules out the most extreme mass-loss rates in the literature. A theory that predicts more moderate mass loss gives a mass function that is closer to observed statistics but still disagrees for M < 1 M_J.

In this Letter we show that it is possible to determine slow velocities (~20 km s^-1) in the extended solar corona by means of the ratio of the resonance doublet of O VI. We apply this technique to a quiescent streamer at solar minimum, observed by the Ultraviolet Coronagraph Spectrometer (UVCS) for 4 consecutive days, and determine the velocity pattern in it. We show that a rapid velocity increase occurs on the lateral sides of the streamer as the distance from the streamer axis increases. We also show that, probably, outflowing plasma exists also in the streamer core. We point out the interest of examining the possible relation of this finding with the reduction of the O VI emission observed by UVCS in the core of some streamers. We also point out the importance of studying the connection of the plasma just outside the v ≃ 20 km s^-1 curve with the streamer cusp, to gain insight in the physics of the slow solar wind.

Using reconstructed opacities, we construct solar models with low heavy-element abundance. Rotational mixing and enhanced diffusion of helium and heavy elements are used to reconcile the recently observed abundances with helioseismology. The sound speed and density of models in which the relative and absolute diffusion coefficients for helium and heavy elements have been increased agree with seismically inferred values at better than the 0.005 and 0.02 fractional levels, respectively. However, the surface helium abundance of the enhanced diffusion model is too low. The low-helium problem in the enhanced diffusion model can be solved to a great extent by rotational mixing. The surface helium and the convection zone depth of rotating model M04R3, which has a surface Z of 0.0154, agree with the seismic results at the levels of 1 σ and 3 σ, respectively. M04R3 is almost as good as the standard model M98. Some discrepancies between the models constructed in accord with the new element abundances and seismic constraints can be solved individually, but it seems difficult to resolve them as a whole.