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SN 1991bg: A Type IA Supernova With a Difference
Suntzeff, N. B.; Walker, A. R.; Caldwell, Nelson +28 more
We present 13 spectra and 31 photometric observations covering the first 150 days of SN 1991bg in NGC 4374 (M 84). Although SN 1991bg was a type Ia supernova displaying the characteristic Si II absorption at 6150 A near maximum and the Fe emission lines at late phases, it varied from the well-defined norm for SNe Ia in several important respects. …
Stellar Kinematic Groups. I. The URSA Major Group
Soderblom, David R.; Mayor, Michel
The Ursa Major Group (UMaG) is studied as a test case for the authenticity of Stellar Kinematic Groups, using Coravel radial velocities, recent compilations of astrometric data, and new spectroscopic observations. Spectroscopic age indicators, particularly indices of the strength of chromospheric emission, are applied to solar-type candidate membe…
Evolution of the Symbiotic Binary System AG Pegasi: The Slowest Classical Nova Ever Recorded
Polidan, Ronald S.; Mikolajewska, Joanna; Slovak, Mark H. +2 more
We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in p…
The Early Ultraviolet Spectral Evolution of Nova Cygni 1992
Ake, T. B.; Shore, Steven N.; Sonneborn, George +2 more
We report on the high resolution ultraviolet line profile evolution of Nova Cygni 1992 using the International Ultraviolet Explorer (IUE) satellite and the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). Our observations cover the period from discovery in 1992 February through 1993 April. The initial expansion velo…
Binary Star Orbits From Speckle Interferometry. V. A Combined Speckle/Spectroscopic Study of the O Star Binary 15 Monocertis
Gies, Douglas R.; Shara, Michael M.; Penny, Laura R. +7 more
We report on the discovery of a speckle binary companion to the O7 V (f) star 15 Monocerotis. A study of published radial velocities in conjunction with new measurements from Kitt Peak National Observatory (KPNO) and IUE suggests that the star is also a spectroscopic binary with a period of 25 years and a large eccentricity. Thus, 15 Mon is the fi…
PG 0308+096 and PG 1026+002: Two New Short Period Binary Stars Resulting From Common-Envelope Evolution
Green, Richard F.; Sion, Edward M.; Saffer, Rex A. +5 more
Ultraviolet spectroscopy, optical spectroscopy, and spectrophotometry have been used to study the excess UV stars PG 0308 + 096 and PG 1026 + 002. Both objects are short-period binary systems, each containing a DA white dwarf star and a dM star. Orbital periods of approximately 0.284 day for PG 0308 + 096, and aproximately 0.597 day for PG 1026, h…
Hubble Space Telescope / Faint Object Camera Observations of the Inner Regions of the Galactic Globular Cluster M15
Paresce, F.; Ferraro, F. R.
A set of high resolution images of the core of the Galactic Globular Cluster M15 (NGC 7078) were obtained for the first time with the Faint Object Camera on the HST through the f/48-F140W, f/48-F220W and f/96-F342W ultraviolet filters. Two UV-Color-Magnitude Diagrams are presented for the approximately 300 objects measured in the 22 arcsec x 22 ar…
IUE Temperatures for White Dwarf Stars in and Around the ZZ Ceti Instability Strip
Kepler, S. O.; Nelan, E. P.
We have analyzed all the archival IUE images of the DA4 and DA5 white dwarfs with model atmosphere fluxes incorporating the quasi-molecular opacities to obtain a consistent set of temperatures for both the variables and nonvariables in and around the ZZ Ceti instability strip. We have found four nonvariable stars inside the instability strip. Take…
RE 1016-053: A Pre-Cataclysmic Binary, and the First Extreme Ultraviolet and X-Ray Detections of DAO White Dwarf
Barstow, M. A.; Bergeron, P.; Holberg, J. B. +4 more
Photometric observations and analysis of the optical, UV, EUV, and X-ray spectra are presented for the EUV/X-ray source RE 1016-53. Multiwavelength observations of RE 1016-53 point out that it is a precataclysmic binary. Optical spectra exhibit the steep blue continuum and Balmer absorption typical of a hot white dwarf, but there are bright, narro…
Chromospherically active Stars. XI. Giants With Compact Hot Companions and the Barium Star Scenario
Henry, Gregory W.; Fekel, Francis C.; Busby, Michael R. +1 more
We have determined spectroscopic orbits for three chromsopherically active giants that have hot compact companions. They are HD 160538 (KO III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (KO III + sdB, P = 20.6619 days). By fitting an IUE spectrum with theoretical models, we find the white dwarf companion…