Search Publications
Modeling the Photoionized Interface in Blister H II Regions
Hester, J. Jeff; Sankrit, Ravi
We present a grid of photoionization models for the emission from photoevaporative interfaces between the ionized gas and molecular cloud in blister H II regions. For the density profiles of the emitting gas in the models, we use a general power-law form calculated for photoionized, photoevaporative flows by Bertoldi. We find that the spatial emis…
Discovery of Millihertz ULTRAVIOLET Quasi-periodic Oscillations in Hercules X-1
Horne, Keith; Boyd, Patricia T.; Boroson, Bram +5 more
Observations of the ultraviolet continuum of the X-ray binary system Her X-1/HZ Herculis with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST) show quasi-periodic oscillations (QPOs) at frequencies of 8+/-2 and 43+/-2 mHz, with rms amplitudes of 2% and 4% of the steady flux. Observations with the Keck Telescope confirm …
Integrating the BEPPOSAX Gamma-Ray Burst Monitor into the Third Interplanetary Network
Frontera, F.; Orlandini, M.; Cline, T. +10 more
We have added the BeppoSAX Gamma-Ray Burst Monitor to the third Interplanetary Network (IPN3) of burst detectors. We analyze 16 bursts whose positions are known to good accuracy from measurements at other wavelengths. We show that there is excellent agreement between the Ulysses/BeppoSAX triangulation annuli and the known positions of these events…
The Abundance of Interstellar Boron
Sembach, Kenneth R.; Savage, Blair D.; Howk, J. Christopher
We use new Space Telescope Imaging Spectrograph (STIS) and archival Goddard High Resolution Spectrograph (GHRS) observations to study interstellar B II λ1362 and O I λ1355 absorption along seven sight lines. Our new column density measurements, combined with measurements of four sight lines from the literature, allow us to study the relative B/O a…
LMC X-2: The First Extragalactic Z Source?
Kuulkers, Erik; Smale, Alan P.
We present RXTE observations of LMC X-2 obtained during a 5 day interval in 1997 December, during which the source was radiating at a mean intensity near the Eddington limit and was strongly variable on timescales of seconds to hours. The shapes of the X-ray color-color and hardness-intensity diagrams during the observations, the presence of very …
Resolved CO (1 --> 0) Nuclei in IRAS 14348-1447: Evidence for Massive Bulge Progenitors to Ultraluminous Infrared Galaxies
Surace, J. A.; Evans, A. S.; Mazzarella, J. M.
High-resolution, CO (1 --> 0) interferometry of the ultraluminous infrared galaxy IRAS 14348-1447 is presented. The merger system has a molecular gas mass of ~3×1010 Msolar and a projected nuclear separation of 4.8 kpc (3.5"), making it one of the most molecular gas-rich galaxies known and an ideal candidate for studying t…
A Compact Population of Red Giants in the Blue Compact Dwarf Galaxy UGCA 290
Greggio, Laura; Hopp, Ulrich; Schulte-Ladbeck, Regina E. +1 more
We present Hubble Space Telescope/Wide Field Planetary Camera 2 single-star photometry for the blue dwarf galaxy UGCA 290, whose morphology is intermediate between classic iE blue compact dwarf galaxies and blue dwarf galaxies that exhibit no red background sheet of older stars. The color-magnitude diagram of this galaxy in V and I, extending over…
Asteroseismology of the Multiply Periodic δ Scuti Star θ Tucanae
Templeton, Matthew R.; Bradley, Paul A.; Guzik, Joyce A.
We present an asteroseismological analysis of the δ Scuti component of the binary star system θ Tucanae, using the 10 pulsational frequencies obtained photometrically by Paparó et al. and the mode identifications of Sterken. We have tested theoretical models with masses between 1.8 and 2.8 Msolar that have solar metal abundances, and we…
On the Inference of Differential Emission Measures Using Diagnostic Line Ratios
McIntosh, Scott W.
Spectroscopic diagnosis of hot optically thin plasmas can be used to infer valuable information about the temperature structure of the emitting plasma volume, through the emission measure differential (DEM) in Te, DEM(Te). However, the uncertainties in atomic parameters (required to model the plasma emission) make such infere…
Hercules X-1: Empirical Models of Ultraviolet Emission Lines
Raymond, John; Bautista, Manuel; Boroson, Bram +4 more
The UV emission lines of Hercules X-1, resolved with the Hubble Space Telescope (HST) Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph, can be divided into broad (FWHM~750 km s-1) and narrow (FWHM~150 km s-1) components. The broad lines can be unambiguously identified with emission from an accreti…