Table of contents

We compute the B-mode polarization power spectrum of the cosmic microwave background from an epoch of inhomogeneous reionization, using a simple model in which H II regions are represented by ionized spherical bubbles with a lognormal distribution of sizes whose clustering properties are determined by large-scale structure. Both the global ionization fraction and the characteristic radius of H II regions are allowed to be free functions of redshift. Models that would produce substantial contamination in degree-scale gravitational wave B-mode measurements have power that is dominated by the shot noise of the bubbles. Rare bubbles of radius ≳100 Mpc at z > 20 can produce signals that in fact exceed the B-modes from gravitational lensing and are comparable to the maximal allowed signal of gravitational waves (~0.1 μK) while still being consistent with global constraints on the total optical depth. Even bubbles down to 20 Mpc at z ~ 15, or 40 Mpc at z ~ 10, can be relevant (0.01 μK) once the lensing signal is removed, either statistically or directly. However, currently favored theoretical models that have ionization bubbles that only grow to such sizes at the very end of a fairly prompt and late reionization produce signals that are at most at these levels.

We use cosmological simulations to explore the large-scale effects of reionization. Since reionization is a process that involves a large dynamic range—from galaxies to rare bright quasars—we need to be able to cover a significant volume of the universe in our simulation without losing the important small-scale effects from galaxies. Here we have taken an approach that uses clumping factors derived from small-scale simulations to approximate the radiative transfer on subcell scales. Using this technique, we can cover a simulation size up to 1280 h^-1 Mpc with 10 h^-1 Mpc cells. This allows us to construct synthetic spectra of quasars similar to observed spectra of Sloan Digital Sky Survey (SDSS) quasars at high redshifts and compare them to the observational data. These spectra can then be analyzed for H II region sizes, the presence of the Gunn-Peterson trough, and the Lyα forest.

We study correlations in spatial orientation between galaxy clusters and their host superclusters using a Hubble volume N-body realization of a concordance cosmology and an analytic model for tidally induced alignments. We derive an analytic form for the distributions of alignment angle as functions of halo mass (M), ellipticity (), distance (r), and velocity (v) and show that the model, after tuning of three parameters, provides a good fit to the numerical results. The parameters indicate a high degree of alignment along anisotropic, collapsed filaments. The degree of alignment increases with M and , while it decreases with r and is independent of v. We note the possibility of using the cluster-supercluster alignment effect as a cosmological probe to constrain the slope of the initial power spectrum.

We describe the angular power spectrum of resolved sources at 3.6 μm (L band) in Spitzer imaging data of the GOODS HDF-N, the GOODS CDF-S, and the NDWFS Boötes field in several source magnitude bins. We also measure angular power spectra of resolved sources in the Boötes field at K_s and J bands using ground-based IR imaging data. In the three bands, J, K_s, and L, we detect the clustering of galaxies on top of the shot-noise power spectrum at multipoles between l ~ 10² and 10⁵. The angular power spectra range from the large, linear scales to small, nonlinear scales of galaxy clustering, and in some magnitude ranges show departure from a power-law clustering spectrum. We consider a halo model to describe clustering measurements and to establish the halo occupation number parameters of IR bright galaxies at redshifts around one. The typical halo mass scale at which two or more IR galaxies with L-band Vega magnitude between 17 and 19 are found in the same halo is between 9 × 10¹¹ and 7 × 10¹²M_☉ at the 1 σ confidence level; this is consistent with the previous halo mass estimates for bright, red galaxies at z ~ 1. We also extend our clustering results and completeness-corrected faint-source number counts in GOODS fields to understand the underlying nature of unresolved sources responsible for IR background (IRB) anisotropies that were detected in deep Spitzer images. While these unresolved fluctuations were measured at subarcminute angular scales, if a high-redshift diffuse component associated with first galaxies exists in the IRB, then it's clustering properties are best studied with shallow, wide-field images that allow a measurement of the clustering spectrum from a few degrees to arcminute angular scales.

We measure the cosmological matter density by observing the positions of baryon acoustic oscillations in the clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We jointly analyze the main galaxies and LRGs in the SDSS DR5 sample, using over half a million galaxies in total. The oscillations are detected with 99.74% confidence (3.0 σ assuming Gaussianity) compared to a smooth power spectrum. When combined with the observed scale of the peaks within the CMB, we find a best-fit value of Ω_M = 0.256 (68% confidence interval) for a flat Λ cosmology when marginalizing over the Hubble parameter and the baryon density. This value of the matter density is derived from the locations of the baryon oscillations in the galaxy power spectrum and in the CMB, and does not include any information from the overall shape of the power spectra. This is an extremely clean cosmological measurement, as the physics of the baryon acoustic oscillation production is well understood, and the positions of the oscillations are expected to be independent of systematics such as galaxy bias.

We have investigated the effect of an assembly history on the evolution of galactic dark matter (DM) halos of 10¹²h^-1M_☉ using constrained realizations of random Gaussian fields. Five different realizations of a DM halo with distinct merging histories were constructed and have been evolved using collisionless high-resolution N-body simulations. Our main results are as follows: A halo evolves via a sequence of quiescent phases of a slow mass accretion intermitted by violent episodes of major mergers. In the quiescent phases, the density is well fitted by an NFW profile, the inner scale radius R_s and the mass enclosed within it remain constant, and the virial radius (R_vir) grows linearly with the expansion parameter a. Within each quiescent phase the concentration parameter (c) scales as a, and the mass accretion history (M_vir) is well described by the Tasitsiomi et al. fitting formula. In the violent phases the halos are not in a virial dynamical equilibrium and both R_s and R_vir grow discontinuously. The violent episodes drive the halos from one NFW dynamical equilibrium to another. The final structure of a halo, including c, depends on the degree of violence of the major mergers and the number of violent events. Next, we find a distinct difference between the behavior of various NFW parameters taken as averages over an ensemble of halos and those of individual halos. Moreover, the simple scaling relations c-M_vir do not apply to the entire evolution of individual halos, and therefore we have the common notion that late-forming halos are less concentrated than early-forming ones. The entire evolution of the halo cannot be fitted by single analytical expressions.

Cosmic dust extinction alters the flux of Type Ia supernovae (SNe Ia). Inhomogeneities in the dust distribution induce correlated fluctuations of the SN fluxes. We find that such correlation can be up to 60% of the signal caused by gravitational lensing magnification, with an opposite sign. Therefore, if not corrected, cosmic dust extinction is the dominant source of systematic uncertainty for future SNe Ia lensing measurement, limiting the overall S/N to be ≲10. On the other hand, SN flux correlation measurements can be used in combination with other lensing data to infer the level of dust extinction. This will provide a viable method to eliminate gray dust contamination from the SN Ia Hubble diagram.

We report the results of an [O III] λ5007 survey for PNe in five galaxies that were hosts of well-observed SNe Ia: NGC 524, NGC 1316, NGC 1380, NGC 1448, and NGC 4526. The goals of this survey are to better quantify the zero point of the maximum magnitude-decline rate relation for SNe Ia and to validate the insensitivity of Type Ia luminosity to parent stellar population using the host galaxy Hubble type as a surrogate. We detected a total of 45 PN candidates in NGC 1316, 44 candidates in NGC 1380, and 94 candidates in NGC 4526. From these data and the empirical planetary nebula luminosity function (PNLF), we derive distances of 17.9, 16.1, and 13.6 Mpc, respectively. Our derived distance to NGC 4526 has a lower precision due to the likely presence of Virgo intracluster PNe in the foreground of this galaxy. In NGC 524 and NGC 1448 we detected no PN candidates down to the limiting magnitudes of our observations. We present a formalism for setting realistic distance limits in these two cases and derive robust lower limits of 20.9 and 15.8 Mpc, respectively. After combining these results with other distances from the PNLF, Cepheid, and surface brightness fluctuation distance indicators, we calibrate the optical and NIR relations for SNe Ia and find that the Hubble constants derived from each of the three methods are broadly consistent, implying that the properties of SNe Ia do not vary drastically as a function of stellar population. We determine a preliminary Hubble constant of H₀ = 77 ± 3 (random) ± 5 (systematic) km s^-1 Mpc^-1 for the PNLF, although more nearby galaxies with high-quality observations are clearly needed.

Measuring the population of obscured quasars is one of the key issues in understanding the evolution of active galactic nuclei (AGNs). With a redshift completeness of 99%, the X-ray sources detected in the Chandra Deep Field South (CDF-S) provide the best sample for this issue. In this paper, we study the population of obscured quasars in CDF-S by choosing the 4-7 keV selected sample, which is less biased by the intrinsic X-ray absorption. The 4-7 keV band-selected samples also filter out most of the X-ray-faint sources with too few counts, for which the measurements of N_H and L_X have very large uncertainties. Simply adopting the best-fit L_{2-10 keV} and N_H, we find that 71% ± 19% (20 out of 28) of the quasars (with intrinsic L_{2-10 keV} > 10⁴⁴ ergs s^-1) are obscured with N_H > 10²² cm^-2. Taking into account the uncertainties in the measurements of both N_H and L_X, conservative lower and upper limits for the fraction are 54% (13 out 24) and 84% (31 out 37). In the Chandra Deep Field North, the number is 29%; however, this is mainly due to the redshift incompleteness. We estimate a fraction of ~50%-63% after correcting for the redshift incompleteness with a straightforward approach. Our results robustly confirm the existence of a large population of obscured quasars.

We present host galaxy velocity dispersions of 12 local (mainly Palomar-Green) QSOs measured directly from the stellar CO absorption features in the H band. The mean bulge dispersion of the QSOs in our sample is 186 km s^-1 with a standard deviation of 24 km s^-1. The measurement of the stellar dispersion in QSOs enables us to place them on observational diagrams such as the local black hole mass-bulge velocity dispersion relation and the fundamental plane of early-type galaxies. Concerning the former relation, these QSOs have higher black hole masses than most Seyfert 1 AGNs with similar velocity dispersions. On the fundamental plane, PG QSOs are located between the regions occupied by moderate-mass and giant ellipticals. The QSO bulge and black hole masses, computed from the stellar velocity dispersions, are of order 10¹¹ and 10⁸M_☉, respectively. The Eddington efficiency of their black holes is on average 0.25, assuming that all of the bolometric luminosity originates from the active nucleus. Our data are consistent with other lines of evidence that Palomar-Green QSOs are related to galaxy mergers with gas-rich components and that they are formed in a manner similar to the most massive ultraluminous infrared galaxies, regardless of their far-infrared emission. However, PG QSOs seem to have smaller host dispersions and different formation mechanisms than QSOs with supermassive black holes of 5 × 10⁸-10⁹M_☉ that accrete at low rates and reside in massive spheroids.

We report new Chandra observations of seven optically faint, z ~ 4 radio-quiet quasars (RQQs). We have combined these new observations with previous Chandra observations of RQQs to create a sample of 174 sources. These sources have 0.1 < z < 4.7, and 10⁴⁴ ergs s^-1 < νL_ν (2500 Å) < 10⁴⁸ ergs s^-1. The X-ray detection fraction is 90%. We find that the X-ray loudness of RQQs decreases with UV luminosity and increases with redshift. The model that is best supported by the data has a linear dependence of optical to X-ray ratio α_ox on cosmic time and a quadratic dependence of α_ox on log L_UV, where α_ox becomes X-ray quiet more rapidly at higher log L_UV. We find no significant evidence for a relationship between the X-ray photon index Γ_x and the UV luminosity, and we find marginally significant evidence that the X-ray continuum flattens with increasing z (2 σ). The Γ_x-z anticorrelation may be the result of X-ray spectral curvature, redshifting of a Compton reflection component into the observed Chandra band, and/or redshifting of a soft excess out of the observed Chandra band. Using the results for Γ_x, we show that the α_ox-z relationship is unlikely to be a spurious result caused by redshifting of the observable X-ray spectral region. A correlation between α_ox and z implies evolution of the accretion process. We present a qualitative comparison of these new results with models for accretion disk emission.

We report the results of a survey for fluorescent Lyα emission carried out in the field surrounding the z = 3.1 quasar QSO 0420-388 using the Focal Reducer/Low Dispersion Spectrograph 2 (FORS2) instrument on the Very Large Telescope (VLT). We first review the properties expected for fluorescent Lyα emitters, compared with those of other nonfluorescent Lyα emitters. Our observational search detected 13 Lyα sources sparsely sampling a volume of ~14,000 comoving Mpc³ around the quasar. The properties of these in terms of (1) the line equivalent width, (2) the line profile, and (3) the value of the surface brightness related to the distance from the quasar all suggest that several of these may be plausibly fluorescent. Moreover, their number is in good agreement with the expectation from theoretical models. One of the best candidates for fluorescence is sufficiently far behind QSO 0420-388 that it would imply that the quasar has been active for (at least) ~60 Myr. Further studies on such objects will give information about protogalactic clouds and on the radiative history (and beaming) of the high-redshift quasars.

We present a ~100 ks Chandra X-ray observation and new VLA radio data of the large-scale, 300 kpc long X-ray jet in PKS 1127-145, a radio-loud quasar at redshift z = 1.18. With this deep X-ray observation we now clearly discern the complex X-ray jet morphology and see substructure within the knots. The X-ray and radio jet intensity profiles are seen to be strikingly different, with the radio emission peaking strongly at the two outer knots while the X-ray emission is strongest in the inner jet region. The jet X-ray surface brightness gradually decreases by an order of magnitude going out from the core. The new X-ray data contain sufficient counts for spectral analysis of the key jet features. The X-ray energy index of the inner jet is relatively flat with α_X = 0.66 ± 0.15 and steep in the outer jet with α_X = 1.0 ± 0.2. We discuss the constraints implied by the new data on the X-ray emission models and conclude that "one-zone" models fail and that at least a two-component model is needed to explain the jet's broadband emission. We propose that the X-ray emission originates in the jet proper while the bulk of the radio emission comes from a surrounding jet sheath. We also consider intermittent jet activity as a possible cause of the observed jet morphology.

Using a large sample of 90 Seyfert 2 galaxies (Sy2s) with spectropolarimetric observations, we test the suggestion that the presence of hidden broad-line regions (HBLRs) in Sy2s depends upon the Eddington ratio. The stellar velocity dispersion and extinction-corrected [O III] luminosity are used to derive the masses of central supermassive black holes and the Eddington ratio. We find that (1) below an Eddington ratio threshold of 10^-1.37, all of the objects but one are non-HBLR Sy2s, while at higher Eddington ratios there is no obvious distinction in the Eddington ratio and black hole mass distributions between Sy2s with and without HBLRs; (2) almost no low-luminosity Sy2s (e.g., L_{[O III]} < 10⁴¹ ergs s^-1) show HBLRs, regardless of the column density of neutral hydrogen; (3) for high luminosities, the possibility of detecting HBLR Sy2s is almost the same as that for non-HBLR Sy2s; and (4) when considering only Compton-thin Sy2s with higher [O III] luminosity (>10⁴¹ ergs s^-1), the detectability of HBLRs is very high, ~85%. These results suggest that AGN luminosity plays a major role in the failure to detect HBLRs in low-luminosity Sy2s, while for high-luminosity Sy2s the detectability of HBLRs depends not only upon the AGN activity, but also upon the torus obscuration.

We build a large sample of Seyfert 2 galaxies (Sy2s) with both optical spectropolarimetric and X-ray data available, in which 29 of the Sy2s have a detection of polarized broad emission lines (PBLs) and 25 do not. We find that for luminous Sy2s with L[O III] > 10⁴¹ ergs s^-1, sources with PBLs have smaller X-ray absorption column densities in comparison to those without PBLs (at a 92.3% confidence level): most of the Sy2s with N_H < 10^23.8 cm^-2 show PBLs (86%; 12 out of 14), while the fraction is much smaller for sources with heavier obscuration (54%; 15 out of 28). The confidence level of the difference in absorption bounces up to 99.1% when using the thickness ("T") ratio (F_{2-10 keV}/F[O III]) as an indicator. We rule out observation or selection bias as the origin for the difference. Our results, for the first time with high statistical confidence, show that, in additional to the activity of the nuclei, the nuclear obscuration also plays an important role in the visibility of PBLs in Sy2s. These results can be interpreted in the framework of the unified model. We can reach these results in the unified model if (1) the absorption column density is higher at large inclinations and (2) the scattering region is obscured at large inclinations.

Recently, it has been suggested that the CO line width [FWHM(CO)] is a surrogate for the bulge velocity dispersion (σ) of the host galaxies of high-redshift quasars, and the black hole-bulge (M_BH-σ) relation obtained with this assumption departs significantly from the M_BH-σ relation in the local universe. In this study, we first present an investigation of the correlation between the CO line width and the bulge velocity dispersion using a sample of 33 nearby Seyfert galaxies. We find that the formula adopted in previous studies, σ = FWHM(CO)/2.35, is generally not a good approximation. Using it, one may underestimate the value of bulge velocity dispersion significantly when the CO line is narrower than 400 km s^-1. By involving the galactic inclination angle i as an additional parameter, we obtain a tight correlation between the inclination-corrected CO line width and the bulge velocity dispersion, namely, FWHM(CO)/ sin i = − (67.16 ± 80.18) + (3.62 ± 0.68) σ. Using this new relation, we can better estimate the bulge velocity dispersion from the CO line width if the galactic inclination is known. We apply this new relation to nine high-redshift quasars with CO line detections and find that they are consistent with the local M_BH-σ relation if their inclination angles are around 15°. The possible smaller inclinations of the high-redshift quasars are preferred because of their relatively greater likelihood of detection, and are also consistent with their relatively smaller CO line widths compared to submillimeter galaxies (SMGs) at high redshift having a similar total amount of molecular gas. Future observations are needed to confirm these results.

We present a new determination of the cluster mass function and velocity dispersion function in a volume ~10⁷h³ Mpc^-3 using data from the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) to determine virial masses. We use the caustic technique to remove foreground and background galaxies. The cluster virial mass function agrees well with recent estimates from both X-ray observations and cluster richnesses. Our determination of the mass function lies between those predicted by the 1 and 3 year WMAP data. We constrain the cosmological parameters Ω_m and σ₈ and find good agreement with WMAP and constraints from other techniques. With the CIRS mass function alone, we estimate Ω_m = 0.24 and σ₈ = 0.92, or σ₈ = 0.84 ±0.03 when holding Ω_m = 0.3 fixed. We also use the WMAP parameters as priors and constrain velocity segregation in clusters. Using the 1 and 3 year results, we infer velocity segregation of σ_gxy/σ_DM ≈ 0.94 ± 0.05 or 1.28 ± 0.06, respectively. The good agreement of various estimates of the cluster mass function shows that it is a useful independent constraint on estimates of cosmological parameters. We compare the velocity dispersion function of clusters to that of early-type galaxies and conclude that clusters comprise the high-velocity end of the velocity dispersion function of dark matter halos. Future studies of galaxy groups are needed to study the transition between dark matter halos containing individual galaxies and those containing systems of galaxies. The evolution of cluster abundances provides constraints on dark energy models; the mass function presented here offers an important low-redshift calibration benchmark.

We present a systematic investigation of X-ray thermal coronae in 157 early-type and 22 late-type galaxies from a survey of 25 hot (kT > 3 keV), nearby (z < 0.05) clusters, based on Chandra archival data. Cool galactic coronae (kT = 0.5-1.1 keV generally) have been found to be common, >60% in L_Ks > 2L_* galaxies. These embedded coronae in hot clusters are generally smaller, less luminous, and less massive than coronae in poor environments, demonstrating the negative effects of hot cluster environments on galactic coronae. Nevertheless, these coronae still manage to survive ICM stripping, evaporation, rapid cooling, and powerful AGN outflows, making them a rich source of information about gas stripping, microscopic transport, and feedback processes in the cluster environment. Heat conduction across the boundary of the coronae has to be suppressed by a factor of ≳100, which implies that the X-ray gas in early-type galaxies is magnetized and the magnetic field plays an important role in energy transfer. The luminous, embedded coronae, with high central density (0.1-0.4 cm^-3), are miniversions of group and cluster cooling cores. As the prevalence of coronae of massive galaxies implies a long lifetime (≳several Gyr), there must be a heat source inside coronae to offset cooling. While we argue that AGN heating may not generally be the heat source, we conclude that SN heating can be enough as long as the kinetic energy of SNe can be efficiently dissipated. Diffuse thermal coronae have also been detected in at least 8 of 22 late-type galaxies in our sample. The fraction of luminous X-ray AGNs (>10⁴¹ ergs s^-1) is not small (~5%) in our sample.

We present preliminary results from a survey of CO emission from members of a volume-limited sample of non-cluster elliptical galaxies. Our intent is to compare the gas properties of these ellipticals to a sample of lenticulars selected using similar criteria. The data, although still sparse, suggest that the cool gas in ellipticals shows the same puzzling upper mass cutoff found in the lenticular galaxies. We find, however, significantly lower detection rates and possibly much lower H₂/H I mass ratios in the ellipticals. The detection rate is higher among the lower mass galaxies, as has been found previously. This seems puzzling given that the deeper potential wells of the larger galaxies ought to make gas retention easier, but perhaps that effect is overwhelmed by feedback from the central supermassive black hole. As we have observed ~40% of our full sample, the conclusions are necessarily tentative at this time.

We present low-resolution spectroscopy of 120 red giants in the Galactic satellite dwarf spheroidal (dSph) Leo I, obtained with GeminiN GMOS and Keck DEIMOS. We find stars with velocities consistent with membership of Leo I out to 1.3 King tidal radii. By measuring accurate radial velocities with a median measurement error of 4.6 km s^-1, we find a mean systemic velocity of 284.2 km s^-1 with a global velocity dispersion of 9.9 km s^-1. The dispersion profile is consistent with being flat out to the last data point. We show that a marginally significant rise in the radial dispersion profile at a radius of 3' is not associated with any real localized kinematical substructure. Given its large distance from the Galaxy, tides are not likely to have affected the velocity dispersion, a statement we support from a quantitative kinematical analysis, as we observationally reject the occurrence of a significant apparent rotational signal or an asymmetric velocity distribution. Mass determinations adopting both isotropic stellar velocity dispersions and more general models yield an M/L of 24, which is consistent with the presence of a significant dark halo with a mass of about 3 × 10⁷M_☉, in which the luminous component is embedded. This suggests that Leo I exhibits dark matter properties similar to those of other dSphs in the Local Group. Our data allowed us also to determine metallicities for 58 of the targets. We find a mildly metal-poor mean of -1.31 dex and a full spread covering 1 dex. In contrast to the majority of dSphs, Leo I appears to show no radial gradient in its metallicities, which points to a negligible role of external influences in this galaxy's evolution.

We present initial results from "Via Lactea," the highest resolution simulation to date of Galactic CDM substructure. It follows the formation of a Milky Way-sized halo with M_halo = 1.8 × 10¹²M_☉ in a WMAP three-year cosmology, using 234 million particles. Over 10,000 subhalos can be identified at z = 0: their cumulative mass function is well-fit by N(> M_sub) = 0.0064 (M_sub/M_halo)^-1 down to M_sub = 4 × 10⁶M_☉. The total mass fraction in subhalos is 5.3%, while the fraction of surface mass density in substructure within a projected distance of 10 kpc from the halo center is 0.3%. Because of the significant contribution from the smallest resolved subhalos, these fractions have not converged yet. Sub-substructure is apparent in all the larger satellites, and a few dark matter lumps are resolved even in the solar vicinity. The number of dark satellites with peak circular velocities above 10 km s^-1 (5 km s^-1) is 124 (812): of these, five (26) are found within 0.1r_vir, a region that appeared practically smooth in previous simulations. The neutralino self-annihilation γ-ray emission from dark matter clumps is approximately constant per subhalo mass decade. Therefore, while in our run the contribution of substructure to the γ-ray luminosity of the Galactic halo amounts to only 40% of the total spherically averaged smooth signal, we expect this fraction to grow significantly as resolution is increased further. An all-sky map of the expected annihilation γ-ray flux reaching a fiducial observer at 8 kpc from the Galactic center shows that at the current resolution a small number of subhalos start to be bright enough to be visible against the background from the smooth density field surrounding the observer.

We analyze HST and FUSE ultraviolet spectroscopic data for 11 sight lines passing through the infalling high-velocity cloud (HVC) Complex C. These sight lines pass through regions with H I column densities in the range N = 10^18.1-10^20.1 cm^-2. From [O I/H I] abundances, we find that Complex C metallicities range from 0.09 to 0.29 Z_☉, with a column density weighted mean of 0.13 Z_☉. Nitrogen (N I) is underabundant by factors of (0.01-0.07)(N/H)_☉, significantly less than oxygen relative to solar abundances. This pattern suggests nucleosynthetic enrichment by Type II SNe, consistent with an origin in the Galactic fountain or infalling gas produced in winds from Local Group galaxies. The range of metallicity and its possible (2 σ) dependence on N could indicate some mixing of primordial material with enriched gas from the Milky Way, but the mixing mechanism is unclear. We also investigate the significant highly ionized component of Complex C, detected in C IV, Si IV, and O VI, but not in N V. High-ion column density ratios show little variance and are consistent with shock ionization or ionization at interfaces between Complex C and a hotter surrounding medium. Evidence for the former mechanism is seen in the Mrk 876 line profiles, where the offset in line centroids between low and high ions suggests a decelerating bow shock.

We report the detection of six discrete, low-luminosity (L_X < 10³³ ergs s^-1) X-ray sources, located within 12'' of the center of the collapsed-core globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass radius, from a 50 ks Chandra ACIS-S exposure. Three sources lie within the very small upper limit of 1.9'' on the core radius. The brightest of the three core sources has a luminosity of L_X(0.5-6 keV) ≈ 6 × 10³² ergs s^-1 and a blackbody-like soft X-ray spectrum, which are both consistent with it being a quiescent low-mass X-ray binary (qLMXB). We have identified optical counterparts to four of the six central sources and a number of the outlying sources, using deep Hubble Space Telescope and ground-based imaging. While the two proposed counterparts that lie within the core may represent chance superpositions, the two identified central sources that lie outside of the core have X-ray and optical properties consistent with being cataclysmic variables (CVs). Two additional sources outside of the core have possible active binary counterparts. We discuss the X-ray source population of M30 in light of its collapsed-core status.

The intense Compton cooling of ultrarelativistic electrons in the Klein-Nishina regime in radiation-dominated environments, such as that found in the Galactic center, may result in radically different electron spectra than those produced by synchrotron cooling. We explore these effects and their impact on the X-ray and γ-ray spectra produced in electron accelerators in this region in comparison to elsewhere in our Galaxy. We discuss the broadband emission expected from the newly discovered pulsar wind nebula G359.95-0.04 and the possible relationship of this X-ray source to the central TeV γ-ray source HESS J1745-290. Finally, we discuss the possible relationship of the Galactic center INTEGRAL source IGR J1745.6-2901 to the TeV emission.

We present the results of near-infrared imaging and spectroscopic observations of the young core-collapse supernova remnant (SNR) G11.2-0.3. In the [Fe II] 1.644 μm image, we first discover long, clumpy [Fe II] filaments within the radio shell of the SNR, together with some faint, knotty features in the interior of the remnant. The filaments are thick and roughly symmetric with respect to the northeast-southwest elongation axis of the central pulsar wind nebula. We have detected several [Fe II] lines and a H I Brγ line toward the peak position of the bright southeastern [Fe II] filament. The derived extinction is large (A_V = 13 mag), and it is the brightest [Fe II] 1.644 μm filament detected toward SNRs to date. By analyzing two [Fe II] 1.644 μm images obtained 2.2 yr apart, we detect a proper motion corresponding to an expansion rate of 0.035'' ± 0.013'' yr^-1 (830 ± 310 km s^-1). In addition to the [Fe II] features, we also discover two small H₂ 2.122 μm filaments. One is bright and along the southeastern boundary of the radio shell, while the other is faint and just outside its northeastern boundary. We have detected the H₂ (2-1) S(3) line toward the former filament and derive an excitation temperature of 2100 K. We suggest that the H₂ filaments are dense clumps in a presupernova circumstellar wind swept up by the SNR shock, while the [Fe II] filaments are probably composed of both shocked wind material and shocked supernova (SN) ejecta. The distribution of [Fe II] filaments may indicate that the SN explosion in G11.2-0.3 was asymmetric, as in Cassiopeia A. Our results support the suggestion that G11.2-0.3 is a remnant of a SN IIL/b interacting with a dense red supergiant wind.

We present high-resolution observations of G5.89-0.39 in CO(1 → 0), ¹³CO(1 → 0), C¹⁸O(1 → 0), and HCO⁺(1 → 0). We characterize the G5.89-0.39 outflow using the ¹³CO emission. The outflow is found to be young, massive, and powerful. We conclude that (1) the outflow is nearly along the line of sight, (2) there is dynamical evidence for entrainment of ambient interstellar material into the outflow, (3) the mass entrainment rate is ~4 × 10^-3M_☉ yr^-1, (4) in the blue lobe, only ~27% of the outflow mass is due to entrainment, and (5) expansion of the outflow lobes perpendicular to the flow axis is occurring at ~1-10 v_sound. A neutral and ionized outflow tracer are compared. Watson and coworkers predicted that if entrainment through the Kelvin-Helmholtz shear instability adds significantly to the outflow mass, a difference in the turbulent velocity widths of neutral and ionized outflow tracers could be measurable. We cannot conclude that the Kelvin-Helmholtz shear instability is the physical process causing this entrainment, but it may operate at a level below our detection limit.

We apply a recently developed theoretical model of helium emission to observations of both the Orion Nebula and a sample of extragalactic H II regions. In the Orion analysis, we eliminate some weak and blended lines and compare theory and observation for our reduced line list. With our best theoretical model we find an average difference between theoretical and observed intensities ⟨I_pred/I_obs − 1⟩ = 6.5%. We argue that both the red and blue ends of the spectrum may have been inadequately corrected for reddening. For the 22 highest quality lines, with 3499 Å ≤ λ ≤ 6678 Å, our best model predicts observations to an average of 3.8%. We also perform an analysis of the reported observational errors and conclude that they have been underestimated. In the extragalactic analysis, we demonstrate the likelihood of a large systematic error in the reported data and discuss possible causes. This systematic error is at least as large as the errors associated with nearly all attempts to calculate the primordial helium abundance from such observations. Our Orion analysis suggests that the problem does not lie in the theoretical models. We demonstrate a correlation between equivalent width and apparent helium abundance of lines from extragalactic sources that is most likely due to underlying stellar absorption. Finally, we present fits to collisionless case B He I emissivities as well as the relative contributions due to collisional excitations out of the metastable 2s³S term.

This paper describes a high-resolution, infrared spectroscopic survey of young, low-mass stars that is designed to identify and characterize pre-main-sequence spectroscopic binaries. This is the first large infrared radial velocity survey of very young stars to date. The frequency and mass ratio distribution of the closest, low-mass binaries bear directly on models of stellar, brown dwarf, and planetary mass companion formation. Furthermore, spectroscopic binaries can provide mass ratios and ultimately masses, independent of assumptions, needed to calibrate models of young star evolution. I present the initial results from observations of a uniform sample of 33 T Tauri M stars in the Ophiuchus molecular cloud. The average mass of this sample is less than that of other young star radial velocity surveys of similar scope by a factor of ~2. Almost every star was observed at 3-4 epochs over 3 yr with the 10 m Keck II telescope and the facility infrared spectrometer NIRSPEC. An internal precision of 0.43 km s^-1 was obtained with standard cross-correlation calibration techniques. Four of the targets are newly discovered spectroscopic binaries, one of which is located in a subarcsecond, hierarchical quadruple system. Three other subarcsecond visual binaries were also serendipitously identified during target acquisition. The spectroscopic multiplicity of the sample is comparable to that of earlier type, pre-main-sequence objects. Therefore, there is no dearth of young, low-mass spectroscopic binary stars, at least in the Ophiuchus region.

We use spectrally dispersed near-IR interferometry data to constrain the temperature profiles of sub-AU-sized regions of 11 Herbig Ae/Be sources. We find that a single-temperature ring does not reproduce the data well. Rather, models incorporating radial temperature gradients are preferred. These gradients may arise in a dusty disk, or may reflect separate gas and dust components with different temperatures and spatial distributions. Comparison of our models with broadband spectral energy distributions suggests the latter explanation. The data support the view that the near-IR emission of Herbig Ae/Be sources arises from hot circumstellar dust and gas in sub-AU-sized disk regions. Intriguingly, our derived temperature gradients appear systematically steeper for disks around higher mass stars. It is not clear, however, whether this reflects trends in relative dust/gas contributions or gradients within individual components.

We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations: GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in the pre-Swift era. However, we find that the X-ray afterglow light curves, which extend up to 10-70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow light curves in our sample satisfy the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen for some unknown reason.

We present a comprehensive study of the morphological properties of 42 γ-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope in the optical band. The purpose of this study is to understand the relation of GRBs to their macroenvironments and to compare the GRB-selected galaxies to other high-redshift samples. We perform both qualitative and quantitative analyses by categorizing the galaxies according to their visual properties and by examining their surface brightness profiles. We find that the majority of the galaxies have approximately exponential profiles, indicative of galactic disks, and have a median effective radius of about 1.7 kpc; ~20% of the hosts are better fit with a bulge-dominated profile. Inspection of the visual morphologies reveals a high fraction of merging and interacting systems, with ~30% showing clear signs of interaction and an additional 30% exhibiting irregular and asymmetric structure, which may be the result of recent mergers; these fractions are independent of redshift and galaxy luminosity. The fraction of mergers appears to be elevated compared to other high-redshift samples (i.e., the HDF), particularly for the low luminosities of GRB hosts (M_B ~ -16 to -21 mag). Finally, we show that GRB hosts clearly follow the size-luminosity relation present in other galaxy samples, but thanks to spectroscopic absorption redshifts they help to extend this relation to fainter luminosities.

The polarization of the supernova SN 2002ic interacting with a dense circumstellar envelope is calculated in the context of the asymmetric version of a previously proposed spherical interaction model. The circumstellar envelope is taken to be oblate. The observed polarization can be reproduced for an aspect ratio of 0.65-0.7, assuming inclination angles of >60°. This model predicts a weak sensitivity of the line profiles to the orientation, which is in agreement with the absence of significant variations of the line profiles among SN 2002ic-like supernovae. We propose a test for distinguishing between the binary and single-star progenitor scenarios on the basis of the polarization distribution function for the growing sample of these events.

We calculate the structure of accretion disks around Kerr black holes for accretion rates = 0.001-10 M_☉ s^-1. Such high- disks are plausible candidates for the central engine of gamma-ray bursts. Our disk model is fully relativistic and accurately treats the microphysics of the accreting matter: neutrino emissivity, opacity, electron degeneracy, and nuclear composition. The neutrino-cooled disk forms above a critical accretion rate _ign that depends on the black hole spin. The disk has an "ignition" radius r_ign where neutrino flux rises dramatically, cooling becomes efficient, and the proton-to-nucleon ratio Y_e drops. Other characteristic radii are r_α, where most of α-particles are disintegrated, r_ν, where the disk becomes ν-opaque, and r_tr, where neutrinos get trapped and advected into the black hole. We find r_α, r_ign, r_ν, and r_tr and show their dependence on . We discuss the qualitative picture of accretion and present sample numerical models of the disk structure. All neutrino-cooled disks regulate themselves to a characteristic state such that: (1) electrons are mildly degenerate, (2) Y_e ~ 0.1, and (3) neutrons dominate the pressure in the disk.

We present the analysis of the high-energy emission of the Galactic black hole binary GX 339-4 in a low/hard state at the beginning of its 2004 outburst. The data from 273 ks of INTEGRAL observations, spread over 4 weeks, are analyzed, along with the existing simultaneous RXTE HEXTE and PCA data. During this period, the flux increases by a factor of ≃3, while the spectral shape is quite unchanged, at least up to 150 keV. The high-energy data allow us to detect the presence of a high-energy cutoff, generally related to thermal mechanisms, and to estimate the plasma parameters in the framework of the Comptonization models. We found an electron temperature of 60-70 keV and an optical depth of around 2.5, with a rather low reflection factor (0.2-0.4). In the last observation, we detected a high-energy excess above 200 keV with respect to thermal Comptonization, while at lower energies the spectrum is practically identical to the previous one taken just 2 days before. This suggests that the low- and high-energy components have a different origin.

We present the results of 7 years of K-band monitoring of the low-mass X-ray binary GRS 1915+105. Positive correlations between the infrared flux and the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency spectrum shows that the orbital period of the system is P_orb = 30.8 ± 0.2 days. The phase and amplitude of the orbital modulation suggests that the modulation is due to the heating of the face of the secondary star. We also report another periodic signature between 31.2 and 31.6 days, most likely due to a superhump resonance. From the superhump period we then obtain a range for the mass ratio of the system, 0.05 < q < 0.12.

We study magnetohydrodynamic (MHD) standing shocks in inflowing plasmas in a black hole magnetosphere. Fast and intermediate shock formation is explored in Schwarzschild and Kerr geometry to illustrate general relativistic effects. We find that nonequatorial standing MHD shocks are physically possible, creating a very hot plasma region close to the event horizon. Shocked downstream plasmas can be heated or magnetized depending on the values of various magnetic field-aligned parameters. Then we may expect high-energy thermal/nonthermal emissions from the shocked region. We present the properties of nonequatorial MHD shocks and discuss the shocked plasma region in the black hole magnetosphere. We also investigate the effects of the poloidal magnetic field and black hole spin on the properties of shocks and show that both effects can modify the distribution of the shock front and shock strength. We find for strong MHD shock formation that fast rotating magnetic fields are necessary. The physics of nonequatorial MHD shocks in the black hole magnetosphere could be very important when we construct the central engine model of various astrophysical phenomena.

We argue, following our earlier works (the "CEBZMC model"), that the phenomenon of twin-peak high-frequency quasi-periodic oscillations (QPOs) observed in black hole X-ray binaries is caused by magnetic coupling (MC) between the accretion disk and the black hole (BH). Due to MC, two bright spots occur at separate radial locations r_in and r_out at the disk surface, energized by a kind of Blandford-Znajek mechanism (BZ). We assume, following the Kluzniak-Abramowicz QPO resonance model, that the Keplerian frequencies at these two locations are in the 3 : 2 ratio. With this assumption, we estimate the BH spins in several sources, including GRO J1655-40, GRS 1915+105, XTE J1550-564, H1743-322, and Sgr A*. We give an interpretation of the "jet line" in the hardness-intensity plane, discussing the parameter space consisting of the BH spin and the power-law index for the variation of the large-scale magnetic field in the disk. Furthermore, we propose a new scenario for the spectral state transitions in BH X-ray binaries based on fluctuations in the densities of the accreting plasma from a companion star.

We report the results of simultaneous observations of the Vela pulsar in X-rays and radio from the RXTE satellite and the Mount Pleasant Radio Observatory in Tasmania. We sought correlations between Vela's X-ray emission and radio arrival times on a pulse-by-pulse basis. At a confidence level of 99.8% we have found significantly higher flux density in Vela's main X-ray peak during radio pulses that arrived early. This excess flux shifts to the "trough" following the second X-ray peak during radio pulses that arrive later. Our results suggest that the mechanism producing the radio pulses is intimately connected to the mechanism producing X-rays. Current models using resonant absorption of radio emission in the outer magnetosphere as a cause of the X-ray emission are explored as a possible explanation for the correlation.

The recent detection of the anomalous X-ray pulsar (AXP) 4U 0142+61 in the mid-infrared with the Spitzer observatory by Z. Wang and coworkers constitutes the first instance of a disk around an AXP. We show, by analyzing earlier optical and near-IR data together with the recent data, that the overall broadband data set can be reproduced by a single model of an irradiated and viscously heated disk.

We present data from INTEGRAL and BeppoSAX satellites showing spectral state transitions of the neutron star, atoll-type, low-mass X-ray binary 4U 1705-44. Its energy spectrum can be described as the sum of one or two blackbody components, a 6.4 keV Fe line, and a component due to thermal Comptonization. In addition, and for the first time in this source, we find a strong signature of Compton reflection, presumably due to illumination of the optically thick accretion disk by the Comptonization spectrum. The two blackbody components, which the soft-state data require, presumably arise from both the disk and the neutron star surface. The Comptonization probably takes place in a hot inner flow irradiated by some of the blackbody photons. The spectral transitions are shown to be associated with variations in the bolometric luminosity, most likely proportional to the accretion rate. Independently of the spectral state, we also see changes in the temperature of the Comptonizing electrons and the strength of Compton reflection.

V838 Her and V4160 Sgr were two of the fastest classical novae ever observed, exhibiting light curve declines of 2 mag in less than 2 days. Both novae also showed strong neon emission lines, indicative of an outburst occurring on an oxygen-neon-magnesium white dwarf. Being the brighter of the two, V838 Her has an extensive set of X-ray to radio observations obtained during its first year after outburst. V4160 Sgr has a more modest set of ultraviolet and optical spectra, which show it to be similar to V838 Her, not just in its light curve evolution but also in its spectral development. The observed attributes imply that these novae occurred on extremely massive white dwarfs. This paper uses the Cloudy photoionization code to fit multiple epochs of emission line spectra to determine the elemental abundances of the ejecta of V838 Her and V4160 Sgr.

Population synthesis tools are used to investigate the population of nonmagnetic cataclysmic variables with unevolved main-sequence-like donors at orbital periods greater than 2.75 hr. In addition to the angular momentum losses associated with gravitational radiation, magnetic braking, and mass loss from the system, we also include the effects of circumbinary disks on the evolution. For a fractional mass input rate into the disk, corresponding to 3 × 10^-4 of the mass transfer rate, the model systems exhibit a bounce at orbital periods greater than 2.75 hr. The simulations reveal that (1) some systems can exist as dwarf novae throughout their lifetime, (2) dwarf novae can evolve into novalike systems, and (3) novalike systems can evolve back into dwarf novae during their postbounce evolution to longer orbital periods. Among these subclasses, novalike cataclysmic variables would be the best candidates to search for circumbinary disks at wavelengths ≳10 μm. The theoretical orbital period distribution is in reasonable accord with the combined population of dwarf novae and novalike systems above the period gap, suggesting the possibility that systems with unevolved donors need not detach and evolve below the period gap as in the disrupted magnetic braking model. The resulting population furthermore reveals the possible presence of systems with small mass ratios and a preference of O/Ne/Mg white dwarfs in dwarf nova systems in comparison to novalike systems. The novalike population furthermore shows a lack of systems with high-mass white dwarfs. The importance of observational bias in accounting for the differing populations is examined, and it is shown that an understanding of these effects is necessary in order to confront the theoretical distributions with the observed ones in a meaningful manner.

From the simultaneous observations of SiO v = 3, J = 2-1 and J = 3-2 masers, SiO v = 3, J = 2-1 maser emission was detected for the first time toward the S-type Mira variable χ Cyg. The line was a single spike and was redshifted with respect to the stellar velocity. The SiO v = 3, J = 3-2 maser emission was not detected from this star. However, for the O-rich Mira variable TX Cam, SiO v = 3, J = 3-2 maser emission was detected, while v = 3, J = 2-1 maser was not detected. Two possible line overlaps were adopted as an explanation of these observational results.

For main-sequence G and K stars we study again the empirical relations between the periods of the activity cycles, P_cyc, and the rotational periods, p_rot. We use the high-quality data selected by Brandenburg, Saar, and Turpin. As found by those authors "the P_cyc increase proportional to the p_rot, along two distinctly different sequences," the active "A" sequence, and the inactive "'I" sequence with cooler and more slowly rotating stars. It is found here that along each sequence the number of rotation periods per activity cycle is nearly the same, but the numbers are different for the different sequences, indicating that probably different kinds of dynamos are working for the stars on the different sequences. The transition from one sequence to the other occurs at a rotation period of 21 days. The rotation periods then increase abruptly by about a factor of 2 for the cooler stars. We suggest that this indicates abruptly increased deep mixing. Along the I sequence the overall dependence of the Ca II emission line fluxes, F(Ca II), on rotation and T_eff is consistent with F(Ca II) ∝ Tp. For the A-sequence stars the dependence of F(Ca II) on rotation seems to be stronger than for the I-sequence stars.

We present Gemini GMOS and Magellan LDSS-3 optical spectroscopy for seven ultracool subdwarf candidates color-selected from the Two Micron All Sky Survey. Five are identified as late-type subdwarfs, including the previously reported sdM9.5 SSSPM 1013-1356 and L subdwarf 2MASS 1626+3925, and a new sdM8.5 2MASS 0142+0523. 2MASS 1640+1231 exhibits spectral features intermediate between a late-type M dwarf and subdwarf, similar to the previously identified high proper motion star SSSPM 1444-2019, and we classify both sources as mild subdwarfs, d/sdM9. 2MASS 1227-0447 is a new ultracool extreme subdwarf, spectral type esdM7.5. Spectral model fits yield metallicities that are consistent with these metallicity classifications. Effective temperatures track with numerical subtype within a metallicity class, although they are not equivalent across metallicity classes. As a first attempt to delineate subtypes in the L subdwarf regime we classify 2MASS 1626+3925 and the previously identified 2MASS 0532+8246 as sdL4 and sdL7, respectively, to reflect their similarity to equivalently classified, solar metallicity L-type field dwarfs over the 7300-9000 Å region. We also detail preliminary criteria for distinguishing L subdwarf optical spectra as a road map for defining this new spectral class. The strong TiO bands and Ca I and Ti I lines in the spectrum of 2MASS 1626+3925 provide further evidence that condensate formation may be inhibited in metal-deficient L subdwarfs. We conclude with a compendium of currently known, optically classified ultracool subdwarfs.

We present near-infrared (1.0-2.4 μm) spectra confirming the youth and cool temperatures of six brown dwarfs and low-mass stars with circumstellar disks toward the Chamaeleon II and Ophiuchus star-forming regions. The spectrum of one of our objects indicates a spectral type of ~L1, making it one of the latest spectral type young brown dwarfs identified to date. Comparing spectra of young brown dwarfs, field dwarfs, and giant stars, we define a 1.49-1.56 μm H₂O index capable of determining spectral type to ±1 subtype, independent of gravity. We have also defined an index based on the 1.14 μm sodium feature that is sensitive to gravity, but only weakly dependent on spectral type. Our 1.14 μm Na index can be used to distinguish young cluster members (τ ≲ 5 Myr) from young field dwarfs, both of which may have the triangular H-band continuum shape that persists for at least tens of Myr. Using T_eff values determined from the spectral types of our objects along with luminosities derived from near and mid-infrared photometry, we place our objects on the H-R diagram and overlay evolutionary models to estimate the masses and ages of our young sources. Three of our sources have inferred ages (τ ≃ 10-30 Myr) that are significantly older than the median stellar age of their parent clouds (1-3 Myr). For these three objects, we derive masses ~3 times greater than expected for 1-3 Myr old brown dwarfs with the bolometric luminosities of our sources. The large discrepancies in the inferred masses and ages determined using two separate, yet reasonable, methods emphasize the need for caution when deriving or exploiting brown dwarf mass and age estimates.

We performed N-body simulations of a dust layer without a gas component and examined the formation process of planetesimals. We found that the formation process of planetesimals can be divided into three stages: the formation of nonaxisymmetric wakelike structures, the creation of aggregates, and the collisional growth of the aggregates. Finally, a few large aggregates and many small aggregates are formed. The mass of the largest aggregate is larger than the mass predicted by the linear perturbation theory. We examined the dependence of system parameters on the planetesimal formation. We found that the mass of the largest aggregates increases as the size of the computational domain increases. However, the ratio of the aggregate mass to the total mass M_aggr/M_total is almost constant, 0.8-0.9. The mass of the largest aggregate increases with the optical depth and the Hill radius of particles.

We present four new exoplanets: HIP 14810b and HIP 14810c, HD 154345b, and HD 187123c. The two planets orbiting HIP 14810, from the N2K project, have masses of 3.9 and 0.76 M_J. We have searched the radial velocity time series of 90 known exoplanet systems and found new residual trends due to additional, long period companions. Two stars known to host one exoplanet have sufficient curvature in the residuals to a one planet fit to constrain the minimum mass of the outer companion to be substellar: HD 68988c with 8 M_J < m sin i < 20 M_J and HD 187123c with 3 M_J < m sin i < 7 M_J, both with P > 8 yr. We have also searched the velocity residuals of known exoplanet systems for prospective low-amplitude exoplanets and present some candidates. We discuss techniques for constraining the mass and period of exoplanets in such cases, and for quantifying the significance of weak RV signals. We also present two substellar companions with incomplete orbits and periods longer than 8 yr: HD 24040b and HD 154345b with m sin i < 20 M_J and m sin i < 10 M_J, respectively.

We reanalyze the precision radial velocity (RV) observations of HD 160691 (μ Ara) by the Anglo-Australian Planet Search Team. The star is supposed to host two Jovian companions (HD 160691b, HD 160691c) in long-period orbits (~630 days and ~2500 days, respectively) and a hot Neptune (HD 160691d) in ~9 day orbit. We perform a global search for the best fits in the orbital parameter space with a hybrid code employing the genetic algorithm and simplex method. The stability of Keplerian fits is verified with the N-body model of the RV signal that takes into account the dynamical constraints (so called GAMP method). Our analysis reveals a signature of the fourth, as yet unconfirmed, Jupiter-like planet HD 160691e in ~307 day orbit. Overall, the global architecture of four-planet configuration recalls the solar system. All companions of μ Ara move in quasi-circular orbits. The orbits of two inner Jovian planets are close to the 2 : 1 mean motion resonance. The alternative three-planet system involves two Jovian planets in eccentric orbits (e ~ 0.3), close to the 4 : 1 MMR, but it yields a significantly worse fit to the data. We also verify a hypothesis of the 1 : 1 MMR in the subsystem of two inner Jovian planets in the four-planet model.

A quantitative specification of a three-dimensional flux rope is examined statistically for comparison to previously published statistical measures of coronal mass ejections (CMEs) as observed by the Solar Maximum Mission (SMM) spacecraft. The three-dimensional geometry that has been previously shown to reproduce statistical measures (average angular widths) of CME image data that show flux-rope morphologies is based on a "hollow" pre-eruption density structure extrapolated into the corona. It is shown that the SMM results are consistent with this hollow flux-rope geometry.

We present a detailed description of the features of solar "micro-type III" radio bursts, which are elements of the so-called type III storms, using long-term observations made by the Geotail and Akebono satellites. Micro-type III bursts are characterized by short-lived, continuous, and weak emission. Their average power is estimated to be well below that of the largest type III bursts, by 6 orders of magnitude. When they occur, these bursts have a distribution of emitted power flux that is different from that of ordinary type III bursts, indicating that they are not just weaker versions of the ordinary bursts. Micro-type III burst activity is not accompanied by significant solar soft X-ray activity. We identify the active regions responsible for micro-type III bursts by examining the concurrence of their development and decay with the bursts. It is found that both micro and ordinary type III bursts can emanate from the same active region without interference, indicating the coexistence of independent electron acceleration processes. It is suggested that the active regions responsible for micro-type III bursts generally border on coronal holes.

The active region NOAA 10486 was one of the most flare-productive regions during solar cycle 23. In this paper, we focus our analysis on the daily evolution of magnetic nonpotentiality for this region from 2003 October 26 to October 30. Daily averaged values of three nonpotential parameters: magnetic shear angle, line-of-sight current, and current helicity of the selected regions along the main neutral lines are calculated using the vector magnetograms obtained at Huairou Solar Observing Station. The magnetic flux evolution and proper motion of magnetic features are also studied in detail for the initial brightening regions of the two large X-class flares (X17 on October 28 and X10 on October 29). The main results are as follows. (1) Three parameters of the magnetic nonpotentiality in the photosphere obviously increased at the impulsively brightening flare sites from at least 1 day before the two large X-class flares, and most of the three parameters decreased after the flares around the main flare regions. (2) The increase of magnetic flux and complex proper motions of the magnetic knots were found to be simultaneously occurring at the non—potentiality developing sites along the main neutral lines. Such increases and motions of the magnetic flux can be explained by the model of emerging twisted flux ropes, and we conclude that the emergence of twisted magnetic flux ropes are a main reason for the development of nonpotentiality along the neutral line and for the production of strong X-class flares.

We reexamine the evolution of the observed tilts θ of spot groups with life spans 2-7 days in the two latitude belts <13° and >13°. Using an iterative procedure, we refine the linear fit between θ and the daily tilt angle changes δθ and obtain reliable estimates of the fit coefficients. We interpret our results in light of the scenario implied by the theoretical model of Longcope & Choudhuri for the subsurface dynamics of parent flux loops of bipolar magnetic regions and arrive at the following conclusions: (1) the parent flux tubes of spot groups possess a nonzero tilt at the onset of rise from the depths of their origin; these "inborn tilts" are ~4°-11° in latitudes <13° and ~3°-15° in latitudes >13°; (2) during the rise the tilt of the omega loops of spot groups living 2-7 days get reduced to ~2°-6° in both the latitude belts, and this calls for reexamination of the role of Coriolis force as understood so far; (3) after emergence of the top of the loop above the surface, magnetic tension in the legs tends to restore the tilt to the inborn tilt on timescales of ~5 to 14 days; and (4) these timescales correspond to field strengths in the range ~14-40 kG for the parent flux loops and are close to the limits set by Fan et al.

By applying theoretical constraints to three-dimensional fits of xenon isotope data from presolar grains, we show that they strongly suggest a nucleosynthesis process that produces "r-process" isotopes without producing s-process isotopes (¹²⁸Xe, ¹³⁰Xe) and without producing the conventional r-process isotope ¹³⁶Xe. It is one of three distinct nucleosynthetic sources that are necessary and sufficient to explain the gross variation in xenon isotopic data across all presolar material. The other source contributing r-process isotopes is responsible for the heavy isotope signature identified in nanodiamonds, which is also present in presolar SiC, and is associated with light isotope enrichment. The relative enrichments of heavy and light isotopes in this component in nanodiamonds and SiC grains are different, implying that the parent nucleosynthetic processes are not inextricably linked. Because minor variations in the isotopic compositions of xenon trapped in nanodiamonds show that two distinct sites contributed nanodiamonds to the early solar system within the average grain lifetime, it is suggested that Type IIa supernovae (SNe IIa) are not the source of the nanodiamonds. The s-process signature derived is consistent with that derived from mixing lines between grain subpopulations for isotopes on the s-process path. This implies that a pure end-member is present in the grains (although not approached in analyses). Our approach is more general and provides a less restrictive set of numerical constraints to be satisfied by proposed theoretical treatments of nucleosynthesis.

We assess the information that HST observations of stellar Lyα lines can provide on the heliosheath, the region of the heliosphere between the termination shock and heliopause. To search for evidence of heliosheath absorption, we conduct a systematic inspection of stellar Lyα lines reconstructed after correcting for ISM absorption (and heliospheric/astrospheric absorption, if present). Most of the stellar lines are well centered on the stellar radial velocity, as expected, but the three lines of sight with the most downwind orientations relative to the ISM flow (χ¹ Ori, HD 28205, and HD 28568) have significantly blueshifted Lyα lines. Since it is in downwind directions that heliosheath absorption should be strongest, the blueshifts are almost certainly caused by previously undetected heliosheath absorption. We make an initial comparison between the heliosheath absorption and the predictions of a pair of heliospheric models. A model with a complex multicomponent treatment of plasma within the heliosphere predicts less absorption than a model with a simple single-fluid treatment, which leads to better agreement with the data. Finally, we find that nonplanetary energetic neutral atom (ENA) fluxes measured by the ASPERA-3 instrument on board Mars Express, which have been interpreted as being from the heliosheath, are probably too high to be consistent with the relative lack of heliosheath absorption seen by HST. This would argue for a local interplanetary source for these ENAs instead of a heliosheath source.

We show that atomic alignment presents a reliable way to study the topology of astrophysical magnetic fields. The effect of atomic alignment arises from modulation of the relative population of the sublevels of the atomic ground state pumped by anisotropic radiation flux. As such aligned atoms precess in the external magnetic field, this affects the properties of the polarized radiation arising from both scattering and absorption by the atoms. As a result, the polarizations of emission and absorption lines depend on the three-dimensional (3D) geometry of the magnetic field as well as the direction and anisotropy of incident radiation. We consider a subset of astrophysically important atoms with hyperfine structure. For emission lines, we obtain the dependencies of the direction of linear polarization on the directions of the magnetic field and the incident pumping radiation. For the absorption lines we establish when the polarization is perpendicular and parallel to the magnetic field. For both emission and absorption lines we find the dependence on the degree of polarization on the 3D geometry of the magnetic field. We claim that atomic alignment provides a unique tool for studying magnetic fields in circumstellar regions, active galactic nuclei (AGNs), and the interplanetary and interstellar media. This tool allows one to study the 3D topology of magnetic fields and establish other important astrophysical parameters. We consider polarization arising from both atoms in the steady state and also those undergoing individual scattering of photons. We demonstrate the utility of atomic alignment for studies of astrophysical magnetic fields by considering a case of sodium alignment in a comet wake.

We show that measurements of stellar proper motions in dwarf spheroidal galaxies provide a powerful probe of the nature of dark matter. Allowing for general dark matter density profiles and stellar velocity anisotropy profiles, we show that the log slope of the dark matter profile at about twice the stellar core (King) radius can be measured to within ±0.2 when the proper motions of 200 stars are added to standard line-of-sight velocity dispersion data. This measurement of the log slope provides a test of cold and warm dark matter theories at a sensitivity not possible with line-of-sight velocity dispersion measurements alone. The upcoming SIM PlanetQuest will have the sensitivity to obtain the required number of proper motions in Milky Way dwarf spheroidal galaxies.

We show that different stellar mass estimation methods yield overall mass scales that disagree by factors up to ~2 for the z = 0 galaxy population and, more importantly, relative mass scales that sometimes disagree by factors ≳3 between distinct classes of galaxies (spiral/irregular types, classical E/S0s, and E/S0s whose colors reflect recent star formation). This comparison considers stellar mass estimates based on (1) two different calibrations of the correlation between K-band mass-to-light ratio and B - R color and (2) detailed fitting of UBRJHK photometry and optical spectrophotometry using two different population synthesis models (Bruzual-Charlot and Maraston), with the same initial mass function in all cases. We also compare stellar+gas masses with dynamical masses. This analysis offers only weak arguments for preferring a particular stellar mass estimation method, given the plausibility of real variations in dynamical properties and dark matter content. These results help to calibrate the systematic uncertainties inherent in mass-based evolutionary studies of galaxies, including comparisons of low- and high-redshift galaxies.

In this Letter, the broad emission line (BEL) profiles of superluminal quasars with apparent jet velocities β_a > 10 (ultraluminal QSOs [ULQSOs]) are studied as a diagnostic of the velocity field of the BEL-emitting gas in quasars. The ULQSOs are useful because they satisfy a very strict kinematical constraint: their parsec-scale jets must be propagating within 12° of the line of sight. We know the orientation of these objects with great certainty. The large BEL FWHM, ~3000-6000 km s^-1, in ULQSOs tend to indicate that the BEL gas has a larger component of axial velocity (either random or in a wind) along the jet direction than previously thought.

Recently, the High Energy Stereoscopic System (HESS) and other air Cerenkov telescopes have detected a source of TeV γ-rays coincident with the Galactic center. It is not yet clear whether the γ-rays are produced via leptonic or hadronic processes, so it is important to consider possible acceleration sites for the charged particles that produce the γ-rays. One exciting possibility for the origin of these particles is the central black hole, Sgr A*, where the turbulent magnetic fields close to the event horizon can accelerate protons to TeV energies. Using a realistic model of the density distribution in a 6 × 6 × 6 pc cube at the Galactic center, we here calculate the trajectories followed by these TeV protons as they gyrate through the turbulent medium surrounding Sgr A*. Diffusing out from the black hole, the protons produce TeV γ-rays via π⁰ decay following a collision with a proton in the surrounding medium. After following over 222,000 such trajectories, we find that the circumnuclear ring around Sgr A* can reproduce the observed 0.1-100 TeV HESS spectrum and flux if the protons are injected into this medium with an effective power-law index ≈0.75, significantly harder than the observed photon index of 2.25. The total energy in the steady state 1-40 TeV proton population surrounding Sgr A* is inferred to be ≈5 × 10⁴⁵ ergs. Only 31% of the emitted 1-100 TeV protons encounter the circumnuclear torus, leaving a large flux of protons that diffuse outward to contribute to the Galactic ridge emission observed by HESS on scales of ≳1°.

We report the first detection of rotational transitions of methyl formate (HCOOCH₃) in the first torsionally excited state (v_t = 1). Recent progress on the assignment of laboratory spectra of methyl formate made it possible for us to assign about 20 unidentified lines in Orion KL from previous line surveys below 200 GHz to the first torsionally excited methyl formate. The rotational temperature and column density obtained in the first torsionally excited state were 44 ± 10 K and (8.6 ± 3.2) × 10¹⁴ cm^-2, respectively. They were compared with those in the ground state.

We report on the first far-IR detection of H₂D⁺, using the Infrared Space Observatory, in the line of sight toward Sgr B2 in the Galactic center. The transition at λ = 126.853 μm connecting the ground level of o-H₂D⁺, 1_{1, 1}, with the 2_{1, 2} level at 113 K is observed in absorption against the continuum emission of the cold dust of the source. The line is broad, with a total absorption covering 350 km s^-1, i.e., similar to that observed in the fundamental transitions of H₂O, OH, and CH at ~179, 119, and 149 μm, respectively. For the physical conditions of the different absorbing clouds, the H₂D⁺ column density ranges from 2 to 5 × 10¹³ cm^-2, i.e., near an order of magnitude below the upper limits obtained from ground-based submillimeter telescopes. The derived H₂D⁺ abundance is of a few times 10^-10, which agrees with chemical model predictions for a gas at a kinetic temperature of ≃20 K.

The recently discovered extended TeV source HESS J1834-087 is associated with both a diffuse X-ray enhancement and a molecular cloud, projected at the center of an old radio supernova remnant, G23.3-0.3 (SNR W41). New H I observations from the VLA Galactic Plane Survey (VGPS) show unambiguous structures associated with W41 in the radial velocity range of 53-63 km s^-1, so we obtain for W41 a distance of 4 ± 0.2 kpc. A new higher sensitivity VGPS continuum image of W41 at 1420 MHz shows faint emission in its eastern part not detected by previous observations, so we provide a new angular size of 36' × 30' in the b-l direction (average radius of 19 pc). We estimate for W41 an age of ~10⁵ yr. A new XMM-Newton observation reveals diffuse X-ray emission within the HESS source and suggests an association between the X-ray and γ-ray emission. The high-resolution ¹³CO images of W41 further reveal a giant molecular cloud (GMC) located at the center of W41, likely associated with W41 in the radial velocity range of 61-66 km s^-1. Altogether, the new observations can be interpreted as providing the first evidence that an old SNR encounters a GMC to emit TeV γ-rays in the cloud material.

We investigate the latitude at which type I X-ray bursts are ignited on rapidly rotating accreting neutron stars. We find that, for a wide range of accretion rates , ignition occurs preferentially at the equator, in accord with the work of Spitkovsky et al. However, for a range of below the critical above which bursts cease, ignition occurs preferentially at higher latitudes. The range of over which nonequatorial ignition occurs is an increasing function of the neutron star spin frequency. These findings have significant implications for thermonuclear flame propagation, and they may explain why oscillations during the burst rise are detected predominantly when the accretion rate is high. They also support the suggestion of Bhattacharyya & Strohmayer that non-photospheric radius expansion double-peaked bursts and the unusual harmonic content of oscillations during the rise of some bursts result from ignition at or near a rotational pole.

We present a 5' × 5' integrated intensity map of ¹²CO (J = 3-2) emission from the ρ Ophiuchi cloud core that traces low-luminosity outflow emission from two protostars: Elias 29 and, most likely, LFAM 26. The morphology of the outflow from Elias 29 is bipolar and has a curved axis that traces the S-shaped symmetry seen in H₂ emission. The outflow from LFAM 26 is a new detection and oriented in the east-west direction near the plane of the sky with most of the blueshifted emission being absorbed by intervening clouds. The outflow axis of this object also appears to intersect a knot of H₂ emission previously attributed to Elias 29. LFAM 26 is a low-luminosity source (L_bol = 0.06 L_☉), which, in combination with the observed outflow, makes it a candidate very low luminosity object (VeLLO). We derive lower limits to the gas column densities and energetics for both outflows. The mechanical luminosities for Elias 29 and LFAM 26 are 6.4 and 10.3 × 10^-3L_☉, respectively.

A radio burst lasting up to 72 hr at a high Galactic latitude was detected by interferometric drift-scanning observation using an eight-element, 20 m diameter fixed spherical dish array at the Waseda Nasu Pulsar Observatory in Japan. Transient fringes of this radio burst, WJN J1443+3439, were observed at 19:39:01 UT on 2005 February 13 and at 19:35:05 UT on 2005 February 14, at α = 14^h43^m22.0^s ± 10.0^s, δ = 34°39' ± 0.4° (J2000.0) (l = 56°55', b = 64°57'). The flux density was 1.5 Jy on February 13, whereas it was 3.0 Jy on February 14. Within the error box, a few possible counterparts at other wavelengths (two X-ray sources and two gamma-ray sources) were considered. One of the X-ray sources, 1WGA J1443.4+3450, is in an unidentified class.

Excess emission from a pointlike source coincident with the central star of the Helix Nebula is detected with Spitzer at 8, 24, and 70 μm. At 24 μm, the central source is superposed on an extended diffuse emission region. While the [O IV] 25.89 μm line contributes to the diffuse emission, a 10-35 μm spectrum of the central source shows a strong thermal continuum. The excess emission from the star most likely originates from a dust disk with blackbody temperatures of 90-130 K. Assuming a simple optically thin debris disk model, the dust is distributed in a ring between ~35 and ~150 AU from the central star, possibly arising from collisions of Kuiper Belt-like objects or the breakup of comets from an Oort-like cloud that have survived from the post-main-sequence evolution of the central star.

Long-time high-resolution simulations of the dynamics of a coronal loop in Cartesian geometry are carried out, within the framework of reduced magnetohydrodynamics (RMHD), to understand coronal heating driven by the motion of field lines anchored in the photosphere. We unambiguously identify MHD anisotropic turbulence as the physical mechanism responsible for the transport of energy from the large scales, where energy is injected by photospheric motions, to the small scales, where it is dissipated. As the loop parameters vary, different regimes of turbulence develop: strong turbulence is found for weak axial magnetic fields and long loops, leading to Kolmogorov-like spectra in the perpendicular direction, while weaker and weaker regimes (steeper spectral slopes of total energy) are found for strong axial magnetic fields and short loops. As a consequence we predict that the scaling of the heating rate with axial magnetic field intensity B₀, which depends on the spectral index of total energy for given loop parameters, must vary from B for weak fields to B for strong fields at a given aspect ratio. The predicted heating rate is within the lower range of observed active region and quiet-Sun coronal energy losses.

Using two-dimensional (2D) magnetohydrodynamic simulations we study the effects of resistive processes in the dynamics of magnetic flux emergence and its relation to Ellerman bombs and other dynamic phenomena in the Sun. The widely accepted scenario of flux emergence is the formation and expansion of Ω-shaped loops due to the Parker instability. Since the Parker instability has the largest growth rate at finite wavelength λ_p ~ 10H-20H, where H is the scale height (≈200 km in the solar photosphere), a number of magnetic loops may rise from the initial flux sheet if it is sufficiently long. This process is shown in our numerical simulations. The multiple emerging loops expand in the atmosphere and interact with each other, leading to magnetic reconnection. At first reconnection occurs in the lower atmosphere, which allows the sinking part of the flux sheet to emerge above the photosphere. This reconnection also causes local heating that may account for Ellerman bombs. In the later stage, reconnection between the expanding loops occurs at higher levels of the atmosphere and creates high-temperature reconnection jets, and eventually a large (≫λ_p) coronal loop is formed. Cool and dense plasma structures, which are similar to Hα surges, are also formed. This is not because of magnetic reconnection but due to the compression of the plasma in between the expanding loops.

We investigate the physical reality of acoustic heating in the solar chromosphere. Evidence is provided that contrary to previous claims by Fossum & Carlsson, high-frequency acoustic waves are indeed sufficient to heat the nonmagnetic solar chromosphere. This assessment is based on three different lines of evidence, which are (1) a discussion of the inherent problems of the limited sensitivity of TRACE when assessing the three-dimensional solar chromospheric topology, (2) a study of the acoustic chromospheric wave energy flux, and (3) a new look at the heating and emission of chromospheric basal flux stars such as τ Ceti.

The millimeter/submillimeter spectrum of the molecular ion FeCO⁺ (X⁴Σ^-) has been recorded using velocity modulation spectroscopy. The molecular ion was created in an AC discharge of Fe(CO)₅ and argon. Twenty-seven rotational transitions, each consisting of four fine-structure components, were measured in the range 198-418 GHz. The data were fit with a case b Hamiltonian, and rotational, spin-rotation, and spin-spin constants were determined. Because of the presence of higher order spin-orbit interactions, probably caused in part by a nearby ⁴Π excited state, numerous centrifugal distortion terms were needed for the spectral analysis. The value of γ_s, the third-order spin-rotation constant, was also remarkably large at -72.4 MHz. Rest frequencies for FeCO⁺ are now available for interstellar and circumstellar searches. This species may be present in molecular clouds, where CO is abundant and gas-phase iron should be in the form of Fe⁺. Molecular ions such as FeCO⁺ could be the hidden carriers of metallic elements in such clouds.