Search Publications
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 …
The Starburst-Interstellar Medium Interaction in NGC 1569. I. Location and Nature of HE II Sources UsingHubble Space Telescope WFPC2 Imagery
Dufour, Reginald J.; Buckalew, Brent A.; Walter, Donald K. +1 more
We present the detection of He II sources in the Im galaxy NGC 1569 from Hubble Space Telescope WFPC2 imagery. Of the 15 detections, seven were Wolf-Rayet stars, five were stellar clusters with associated He II emission, and three were sources of unknown origin. The detected Wolf-Rayet stars' colors and magnitudes are similar to those of Large Mag…
Eclipse mapping of the accretion stream in UZ Fornacis
Gänsicke, B. T.; Beuermann, K.; Kube, J.
We present a new method to map the surface brightness of the accretion streams in
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…
Counts and Sizes of Galaxies in the Hubble Deep Field South: Implications for the Next Generation Space Telescope
Gardner, Jonathan P.; Satyapal, Shobita
Science objectives for the Next Generation Space Telescope (NGST) include a large component of galaxy surveys, both imaging and spectroscopy. The Hubble Deep Field data sets include the deepest observations ever made in the ultraviolet, optical, and near-infrared, reaching depths comparable to that expected for NGST spectroscopy. We present the so…
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 …
Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. IV. The northern hemisphere sample
Tagliaferri, G.; de Medeiros, J. R.; Messina, S. +4 more
We present high-precision photometry, high- and medium-resolution spectroscopy for a sample of 32 stars likely to be the optical counterparts of X-ray sources serendipitously detected by the EXOSAT satellite. Using also recent results from the Hipparcos satellite, we infer spectral types, compute X-ray luminosities and Li abundances and investigat…
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…
Blind source separation and analysis of multispectral astronomical images
Bijaoui, A.; Nuzillard, D.
Celestial sources are studied by means of multispectral analysis, for which a pixel value can be considered as a mixture of different sources. We show that the application of blind source separation methods can display interesting features, which can help astronomers to improve their description of celestial sources. Experiments were carried out o…