Table of contents

We give detailed predictions for the spectral signatures arising from photon–particle oscillations in astrophysical objects. The calculations include quantum electrodynamic effects and effects due to active relativistic plasma. We show that, by studying the spectra of compact sources, it may be possible to directly detect (pseudo-)scalar particles, such as the axion, with much greater sensitivity, by up to three orders of magnitude, than is currently achievable by other methods. In particular, if such particles exist with masses m_a < 10⁻² eV and coupling constant to the electromagnetic field, g > 10⁻¹³ GeV⁻¹, then their oscillation signatures are likely to be lurking in the spectra of magnetars, pulsars, and quasars.

We provide computationally convenient expressions for all marginal distributions of the polarization cosmic microwave background (CMB) power spectrum distribution P(C_ℓ|σ_ℓ), where C_ℓ = {C^TT_ℓ, C^TE_ℓ, C^EE_ℓ, C^BB_ℓ} denotes the set of ensemble-averaged polarization CMB power spectra, and σ_ℓ = {σ^TT_ℓ, σ^TE_ℓ, σ^EE_ℓ, σ^BB_ℓ} the set of the realization-specific polarization CMB power spectra. This distribution describes the CMB posterior power spectrum for cosmic variance limited data. The expressions derived here are general, and may be useful in a wide range of applications. Two specific applications are described in this paper. First, we employ the derived distributions within the CMB Gibbs sampling framework and demonstrate a new conditional CMB power spectrum sampling algorithm that allows for different binning schemes for each power spectrum. This is useful because most CMB experiments have very different signal-to-noise ratios for temperature and polarization. Second, we provide new Blackwell–Rao estimators for each of the marginal polarization distributions, which are relevant to power spectrum and likelihood estimation. Because these estimators represent marginals, they are not affected by the exponential behavior of the corresponding joint expression, but converge quickly.

Calculated and recently measured photoabsorption transition probabilities of the H₂npσ¹Σ⁺_u and npπ¹Π_u − X¹Σ⁺_g band systems have been examined with high-resolution (Δλ = 95–115 mÅ) electron-impact induced emission spectra obtained previously by Jonin et al. and Liu et al. When localized rovibronic coupling is insignificant, transition probabilities calculated with the adiabatic approximation are found to be generally consistent with experiment. However, in the presence of significant coupling, the transition probabilities obtained from a nonadiabatic calculation of B'¹Σ⁺_u, D¹Π⁺_u, $B^{\prime \prime }\bar{B}\,^{1}\Sigma _{u}^{+}$, D'¹Π⁺_u, and 5pσ¹Σ⁺_u state coupling give better agreement with the experimental spectra. Emission yields obtained by comparison of the calculated and experimental spectra are also consistent with the measured predissociation and autoionization yields. In addition, more accurate excitation and emission cross sections and nonradiative yields have been obtained for a number of the npσ¹Σ⁺_u and npπ¹Π_u states. The results obtained in the present investigation lead to a significantly more accurate calibration of the CassiniUVIS instrument and laboratory spectrometers in the range 790–920 Å. They are also an important step toward an accurate model of extreme ultraviolet H₂ auroral and dayglow emissions in the outer planet atmospheres.

We present catalogs of globular cluster candidates for the 100 galaxies of the Advanced Camera for Surveys Virgo Cluster Survey, a large program to carry out imaging of early-type members of the Virgo Cluster using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. We describe the procedure used to select bona fide globular cluster candidates out of the full list of detections based on model-based clustering methods with the use of expected contamination catalogs constructed using blank field observations and which are customized for each galaxy. We also present the catalogs of expected contaminants for each of our target galaxies. For each detected source we measure its position, magnitudes in the F475W (≈ Sloan g) and F850LP (≈ Sloan z) bandpasses, and half-light radii by fitting point-spread function convolved King models to the observed light distribution. These measurements are presented for 20,375 sources, of which 12,763 are likely to be globular clusters. Finally, we detail the calculation of the aperture corrections adopted for the globular cluster photometry.

We present a catalog of 1,172,157 quasar candidates selected from the photometric imaging data of the Sloan Digital Sky Survey (SDSS). The objects are all point sources to a limiting magnitude of i = 21.3 from 8417 deg² of imaging from SDSS Data Release 6 (DR6). This sample extends our previous catalog by using the latest SDSS public release data and probing both ultraviolet (UV)-excess and high-redshift quasars. While the addition of high-redshift candidates reduces the overall efficiency (quasars:quasar candidates) of the catalog to ∼80%, it is expected to contain no fewer than 850,000 bona fide quasars, which is ∼8 times the number of our previous sample and ∼10 times the size of the largest spectroscopic quasar catalog. Cross-matching between our photometric catalog and spectroscopic quasar catalogs from both the SDSS and 2dF survey yields 88,879 spectroscopically confirmed quasars. For judicious selection of the most robust UV-excess sources (∼500, 000 objects in all), the efficiency is nearly 97%—more than sufficient for detailed statistical analyses. The catalog's completeness to type 1 (broad-line) quasars is expected to be no worse than 70%, with most missing objects occurring at z < 0.7 and 2.5 < z < 3.0. In addition to classification information, we provide photometric redshift estimates (typically good to Δz ± 0.3 [2σ]) and cross-matching with radio, X-ray, and proper-motion catalogs. Finally, we consider the catalog's utility for determining the optical luminosity function of quasars and are able to confirm the flattening of the bright-end slope of the quasar luminosity function at z ∼ 4 as compared to z ∼ 2.

We characterize the crystalline-silicate content and spatial distribution of small dust grains in a large sample of protoplanetary disks in the Taurus-Auriga young cluster, using the Spitzer Space Telescope mid-IR spectra. In turn we use the results to analyze the evolution of structure and composition of these 1–2 Myr old disks around Solar- and later-type young stars, and test the standard models of dust processing which result in the conversion of originally amorphous dust into minerals. We find strong evidence of evolution of the dust-crystalline mass fraction in parallel with that of the structure of the disks, in the sense that increasing crystalline mass fraction is strongly linked to dust settling to the disk midplane. We also confirm that the crystalline silicates are confined to small radii, r ≲ 10 AU. However, we see no significant correlation of crystalline mass fraction with stellar mass or luminosity, stellar-accretion rate, disk mass, or disk/star mass ratio, as would be expected in the standard models of dust processing based upon photoevaporation and condensation close to the central star, accretion-heating-driven annealing at r ≲ 1 AU, or spiral-shock heating at r ≲ 10 AU, with or without effective large-scale radial mixing mechanisms. Either another grain-crystallizing mechanism dominates over these, or another process must be at work within the disks to erase the correlations they produce. We propose one of each sort that seems to be worth further investigation, namely X-ray heating and annealing of dust grains, and modulation of disk structure by giant-planetary formation and migration.

We present the AEGIS-X survey, a series of deep Chandra ACIS-I observations of the Extended Groth Strip. The survey comprises pointings at eight separate positions, each with nominal exposure of 200 ks, covering a total area of approximately 0.67 deg² in a strip of length 2 degrees. We describe in detail an updated version of our data reduction and point-source-detection algorithms used to analyze these data. A total of 1325 band-merged sources have been found to a Poisson probability limit of 4 × 10⁻⁶, with limiting fluxes of 5.3 × 10⁻¹⁷ erg cm² s⁻¹ in the soft (0.5–2 keV) band and 3.8 × 10⁻¹⁶ erg cm⁻² s⁻¹ in the hard (2–10 keV) band. We present simulations verifying the validity of our source-detection procedure and showing a very small, <1.5%, contamination rate from spurious sources. Optical/NIR counterparts have been identified from the DEEP2, CFHTLS, and Spitzer/Infrared Array Camera (IRAC) surveys of the same region. Using a likelihood ratio method, we find optical counterparts for 76% of our sources, complete to R_AB = 24.1, and, of the 66% of the sources that have IRAC coverage, 94% have a counterpart to a limit of 0.9 μJy at 3.6 μm (m_AB = 23.8). After accounting for (small) positional offsets in the eight Chandra fields, the astrometric accuracy of Chandra positions is found to be 08 rms; however, this number depends both on the off-axis angle and the number of detected counts for a given source. All data products described in this paper are made available via a public Web site.

New MK spectral classifications are given for 145 spectroscopic binaries (SBs) with AF primaries because two-dimensional types are lacking for more than one-third of the AF SBs with known orbital elements in the current catalog. Compared with the classifications by Morgan, Keenan, and their students, the new classifications give types that are 1.1 ± 0.2 subclasses later and 0.7 ± 0.1 luminosity classes fainter. Also listed are selected published MK types from Brian Skiff's recent compilation.

Eight ground-state inversion transitions of H₃O⁺ in the 0.9–1.6 THz region have been measured using the frequency multiplier submillimeter spectrometer at Jet Propulsion Laboratory. The accuracy of these measurements is estimated to be 300 kHz. The ions were generated in a dc discharge through a gas mixture of a few mTorr of H₂ and 30 mTorr of H₂O. A multistate analysis was carried out for H₃O⁺, which includes the lines observed in this work, previous submillimeter and terahertz inversion transitions in the ground state, and previous infrared data on all the four vibrational fundamental bands. Accurate molecular parameters were obtained with taking into account the strong Coriolis interaction between the symmetric OH stretching mode (ν₁) and the doubly degenerate asymmetric OH stretching mode (ν₃). Fequency predictions, particularly for high-J transitions in the ground state and in the ν₁ and ν₃ fundamental bands, have been greatly improved by including ∼ 200 more high-J transitions in our analysis, which were excluded in previous analyses. The more precise measurements and new predictions reported here will support the analyses of astronomical observations by the future high-resolution spectroscopy telescopes, such as Herschel, SOFIA, and ALMA.

We report total abundances and related parameters for the full sample of the Far Ultraviolet Spectroscopic Explorer survey of molecular hydrogen in 38 translucent lines of sight. New results are presented for the "second half" of the survey involving 15 lines of sight to supplement data for the first 23 lines of sight already published. We assess the correlations between molecular hydrogen and various extinction parameters in the full sample, which covers a broader range of conditions than the initial sample. In particular, we are now able to confirm that many, but not all, lines of sight with shallow far-UV extinction curves and large values of the total-to-selective extinction ratio, R_V = A_V/E(B − V)—characteristic of larger than average dust grains—are associated with particularly low hydrogen molecular fractions ($f_{\rm H_2}$). In the lines of sight with large R_V, there is in fact a wide range in molecular fractions, despite the expectation that the larger grains should lead to less H₂ formation. However, we see specific evidence that the molecular fractions in this sub-sample are inversely related to the estimated strength of the UV radiation field and thus the latter factor is more important in this regime. We have provided an update to previous values of the gas-to-dust ratio, N(H_tot)/E(B − V), based on direct measurements of N(H₂) and N(H i). Although our value is nearly identical to that found with Copernicus data, it extends the relationship by a factor of 2 in reddening. Finally, as the new lines of sight generally show low-to-moderate molecular fractions, we still find little evidence for single monolithic "translucent clouds" with $f_{\rm H_2} \sim 1$.

The polarization of light across individual spectral lines contains information about the circumstellar environment on very small spatial scales. We have obtained a large number of high-precision, high-resolution spectropolarimetric observations of Herbig Ae/Be, Classical Be and other emission-line stars collected on 117 nights of observations with the Hi-Resolution Visible spectropolarimeter at a resolution of R = 13, 000 on the 3.67 m Advanced Electro-Optical System telescope. We also have many observations from the ESPaDOnS spectropolarimeter at a resolution of R = 68, 000 on the 3.6 m Canada-France-Hawaii Telescope. In roughly ∼2/3 of the so-called "windy" or "disky" Herbig Ae/Be stars, the detected H_α linear polarization varies from our typical detection threshold near 0.1% to over 2%. In all but one HAe/Be star, the detected polarization effect is not coincident with the H_α emission peak but is detected in and around the obvious absorptive part of the line profile. The qu-loops are dominated by the polarization in this absorptive region. In several stars, the polarization varies in time mostly in the absorptive component and is not necessarily tied to corresponding variations in intensity. This is a new result not seen at lower resolution. In the Be and emission-line stars, ten out of a sample of 30 show a typical broad depolarization effect but four of these ten show weaker effects only visible at high resolution. Another five of 30 show smaller amplitude, more complex signatures. Six stars of alternate classification showed large amplitude (1%–3%) absorptive polarization effects. These detections are largely inconsistent with the traditional disk-scattering and depolarization models.

The infrared absorption features of solid carbon dioxide have been detected by space-based observatories in nearly all lines of sight probing the dense interstellar medium (ISM). It has also been shown that the absorption feature of solid CO₂ near 658 cm⁻¹ (15.2 μm) should be a sensitive indicator of the physical conditions of the ice (e.g., temperature and composition). However, the profile structure of this feature is not well understood, and previous laboratory studies have concentrated on a limited range of temperatures and compositions for comparisons with observed spectra from both the Infrared Space Observatory and the Spitzer Space Telescope. In the laboratory study described here, the infrared spectra of ices bearing H₂O, CH₃OH, and CO₂ have been measured with systematically varying compositions and temperatures that span the range of the values expected in the ISM. The mid-IR spectra (λ = 2.5–25 μm) were measured for 47 different ice compositions at temperatures ranging from ∼5.5 K to evaporation, at 5 K intervals.

We report on the catalog of gamma-ray bursts (GRBs) detected with the Gamma-Ray Burst Monitor aboard the BeppoSAX satellite. It includes 1082 GRBs with 40–700 keV fluences in the range from 1.3 × 10⁻⁷ to 4.5 × 10⁻⁴ erg cm⁻², and 40–700 keV peak fluxes from 3.7 × 10⁻⁸ to 7.0 × 10⁻⁵ erg cm⁻² s⁻¹. We report in the catalog some relevant parameters of each GRB and discuss the derived statistical properties.