Search Publications
The Statistical and Physical Properties of the Low-Redshift LYα Forest Observed with the Hubble Space Telescope/STIS
Tripp, Todd M.; Davé, Romeel
We examine the Lyα absorber population at z<0.3 detected in spectra of the quasars PG 0953+415 and H1821+643 taken with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We compare their statistical properties to those in carefully constructed mock quasar spectra drawn from a cosmological hydrodynamic simulation of a…
Far-Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption toward 3C 273
Sembach, Kenneth R.; Savage, Blair D.; Shull, J. Michael +2 more
We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C 273. We identify Lyβ absorption in eight of the known intergalactic Lyα absorbers along the sight line with rest-frame equivalent widths W…
Heavy X-Ray Absorption in Soft X-Ray-weak Active Galactic Nuclei
Brandt, W. N.; Elvis, M.; Gallagher, S. C. +4 more
Recent ROSAT studies have identified a significant population of active galactic nuclei (AGNs) that are notably faint in soft X-rays relative to their optical fluxes. Are these AGNs intrinsically X-ray weak or are they highly absorbed? Brandt, Laor, & Wills have systematically examined the optical and UV spectral properties of a well-defined s…
A Spatially Resolved, Semiempirical Model for the Extended Atmosphere of α Orionis (M2 Iab)
Harper, Graham M.; Brown, Alexander; Lim, Jeremy
We have constructed a detailed mean density and temperature model for the extended outer atmosphere of the O-rich supergiant Betelgeuse (α Ori [M2 Iab]), which extends from 1.0 to 10.0 stellar radii. A one-dimensional model is based on fitting NRAO1 VLA centimeter visibility data, and two-dimensional models are constructed using the intensity cont…
Oxygen in the Very Early Galaxy
Basri, Gibor; Israelian, Garik; Rebolo, Rafael +4 more
Oxygen abundances in a sample of ultra-metal-poor subdwarfs have been derived from measurements of the oxygen triplet at 7771-5 Å and OH lines in the near-UV performed in high-resolution and high signal-to-noise ratio spectra obtained with WHT/UES, Keck I/HIRES, and VLT/UVES. Our Fe abundances were derived in LTE and then corrected for non-LTE (NL…
The Redshift and the Ordinary Host Galaxy of GRB 970228
Bloom, J. S.; Djorgovski, S. G.; Kulkarni, S. R.
The gamma-ray burst of 1997 February 28 (GRB 970228) ushered in the discovery of the afterglow phenomenon. Despite intense study of the nearby galaxy, however, the nature of this galaxy and the distance to the burst eluded the community. Here we present the measurement of the redshift of the galaxy, the putative host galaxy of GRB 970228, and, bas…
Cusped Mass Models of Gravitational Lenses
Keeton, C. R.; Kochanek, C. S.; Muñoz, J. A.
Recent observations of galaxy luminosity profiles and dark matter simulations find luminosity and mass distributions characterized by central cusps rather than finite core radii. We introduce and implement a set of cusped ellipsoidal lens models that include limits similar to the Jaffe, Hernquist, η and NFW models and apply them to the gravitation…
A Study of Chromospheric Oscillations Using the SOHO and TRACE Spacecraft
Wilhelm, Klaus; Judge, Philip G.; Tarbell, Theodore D.
We analyze line and continuum time-series data of the solar atmosphere, with between 10 and 60 s cadence, using the MDI and SUMER instruments on the SOHO spacecraft and the UV bandpasses on the TRACE satellite. The co-aligned data sets sample spectral features formed from photosphere to the middle transition region, spanning five decades in pressu…
Old Stellar Populations of the Small Magellanic Cloud
Dolphin, Andrew E.; Schommer, Robert A.; Mateo, Mario +4 more
We present WFPC2 and ground-based VI photometry of NGC 121 and a nearby field in the outer SMC. For NGC 121, we measure a true distance modulus of µ0=18.96+/-0.04 (distance of 61.9+/-1.1 kpc), age of 10.6+/-0.5 Gyr, metallicity of [Fe/H]=-1.03+/-0.06, and initial mass of 4.1+/-0.4×105 Msolar, assuming a Salpe…
Evidence for the Heating of Atomic Interstellar Gas by Polycyclic Aromatic Hydrocarbons
Dale, Daniel A.; Malhotra, Sangeeta; Helou, George +2 more
We report a strong correlation between the [C II] 158 µm cooling line and the mid-infrared flux in the 5-10 µm range in a wide variety of star-forming galaxies. The mid-infrared flux is dominated by the aromatic features in emission (AFEs), which are thought to arise from large polycyclic aromatic hydrocarbons (PAHs) and are generally …