Search Publications
Dying Pulse Trains in Cygnus XR-1: Evidence for an Event Horizon?
Dolan, Joseph F.
The X-ray-emitting component in the Cyg XR-1/HDE 226868 system is a leading candidate for identification as a stellar-mass-sized black hole. The detection of an event horizon surrounding the point singularity in such a system would constitute a positive identification of a black hole as predicted by general relativity. One signature of such an eve…
Spectroscopy of Massive Stars in NGC 6822 and M33
Bianchi, Luciana; Hutchings, John B.; Scuderi, Salvatore +1 more
We present blue spectra of massive stars in the Local Group galaxies NGC 6822 and M33. For all the targets, selected from our previous Hubble Space Telescope WFPC2 photometry, no previous spectroscopic studies exist, to our knowledge, except for a bright Wolf-Rayet star in NGC 6822. Photospheric parameters Teff and gravity are derived b…
Hubble Space Telescope Photometry of Clusters of Galaxies behind the Dwarf Irregular Galaxies DDO 216 and IC 1613 and the Small Magellanic Cloud
Hodge, Paul W.; Krienke, Karl
We have measured the integrated colors of galaxies in clusters located behind the dwarf irregular galaxies DDO 216 (Pegasus) and IC 1613 and a position in the Small Magellanic Cloud (SMC) near the cluster Lindsey 31. We examine limits on the accuracy of using these for studying the total extinction in galaxies. We show that the method is feasible …
Hubble Space Telescope Color-Magnitude Data for Globular Clusters. I. Transformations between STIS LP Magnitudes and WFPC2 F606W and F814W Magnitudes
Wyse, Rosemary F. G.; Gilmore, Gerard; Houdashelt, Mark L.
We present deep Hubble Space Telescope optical imaging observations of two Galactic globular clusters, 47 Tucanae and M15, using the Space Telescope Imaging Spectrograph (STIS) longpass (LP) filter and the Wide Field and Planetary Camera 2 (WFPC2) F606W and F814W filters. These globular clusters have very different metallicities ([Fe/H]~-0.7 dex f…
The Accretion Disk and White Dwarf during the Quiescence of the Dwarf Novae VW Vulpeculae and χ Leonis
Sion, Edward M.; Henry, Colleen K.
We have carried out an International Ultraviolet Explorer archival comparative study of the two U Geminorum type dwarf novae VW Vulpeculae and χ Leonis. The spectrum of χ Leo does not show any C IV, a feature normally seen in the vast majority of other dwarf novae. For VW Vul, a single-temperature high-gravity photosphere does not produce a consis…
The Orbit and Spectral Line Variations of the Massive Binary HD 163181 (V453 Scorpii)
Wang, Z.; Gies, D. R.; Bagnuolo, W. G., Jr. +3 more
We present revised orbital elements for the massive interacting binary HD 163181, and we offer the first evidence of apsidal motion in the orbit (apsidal period U=510+/-100 yr). We searched for but found no obvious evidence of the secondary's spectral lines in our optical spectra. We do observe, however, systematic profile variations with orbital …
The Confusion Limit on Astrometry with the Space Interferometry Mission
Böker, Torsten; Allen, Ronald J.; Rajagopal, Jayadev
An important requirement for the Space Interferometry Mission (SIM) is to carry out precision astrometry in crowded fields. This capability is crucial, for example, to accurately measure proper motions of bright stars in nearby galaxies. From such measurements, one can obtain distance estimates, explore the dynamics of these systems, and measure t…
The 3-D Heliosphere at Solar Maximum
Marsden, Richard G.
Conference was held in Noordwijk, Netherlands, in 2000 October. Proceedings will be edited by R. G. Marsden and published in Space Science Reviews.
A Study of the Wavelength Calibration of NEWSIPS High-Dispersion Spectra
Smith, Myron A.
In this study we cross-correlate many IUE echellograms of a variety of well-observed stars to evaluate systematic error sources in the wavelength zero points (velocities) of all three cameras. We first evaluate differences between the final archived (``NEWSIPS'') and the originally processed (``IUESIPS'') echellograms. These show a marked time dep…
The Underlying White Dwarf Accretor in the Dwarf Nova UU Aquilae
Sion, Edward M.; Stump, Michael
We present a high-gravity, solar composition model atmosphere and model accretion disk study of the U Gem type dwarf nova UU Aql. We have identified the far-UV signature of the underlying white dwarf for the first time. Our best-fit model atmosphere to the observed far-UV spectrum in quiescence is 27,000+/-1000 K. The solar abundance high-gravity …