Search Publications
Multifrequency Observations of the Superluminal Quasar 3C 345
Bregman, Joel N.; Rieke, G. H.; Matthews, K. +27 more
The authors have investigated the continuum properties of the superluminal quasar 3C 345 with monitoring studies at radio, optical, infrared, and X-ray frequencies. The data presented here include optical, infrared, and radio measurements for a period of 20 yr, far-infrared fluxes obtained with IRAS, and X-ray fluxes taken with the Einstein Observ…
Temperatures for Hot and Pulsating DB White Dwarfs Obtained with the IUE Observatory
Hansen, C. J.; Winget, D. E.; Green, Richard F. +5 more
Ultraviolet energy distributions are presented for 12 hot, helium-atmosphere DB white dwarfs, including the four known pulsating stars which define an empirical DB instability strip. Temperatures are derived exclusively from fits to the ultraviolet energy distributions, especially in the λλ1200 - 2000 region which is most sensitive to temperature.…
On the Nature of the Dwarf Carbon Star G77-61
Liebert, James; Dahn, Conard C.; Mould, Jeremy +4 more
A variety of new astrometric, photometric, and spectrophotometric data are presented for the low-luminosity carbon star G77-61. The improved parallax yields Mv = +10.08±0.43, while the revised temperature estimate from infrared, optical, and ultraviolet fluxes in 4100 (+200, -300)K, yielding logL/L_sun; = -1.75±0.16. Most importantly, r…
Discovery of Rapid Quasi-periodic Oscillations in Scorpius X-1
Priedhorsky, W. C.; Middleditch, J.
The X-ray flux from Sco X-1 can vary quasi-periodically. Fourier analysis of 5-20 keV X-ray data taken while the source was quiescent shows a power density peak at 6 Hz, with a 2 Hz FWHM, and which corresponds to 5 percent of the flux (rms amplitude). No 6 Hz peak was observed when the source was more active, but rather a broad distribution of exc…
DA White Dwarf Effective Temperatures Determined from IUE Lyman-Alpha Profiles
Wesemael, F.; Holberg, J. B.; Basile, J.
The Lyman-alpha profiles of 12 DA white dwarfs have been obtained with the International Ultraviolet Explorer Satellite. Analysis of these profiles provides an improved, uniform, and relatively bias-free measure of effective temperature for these stars over the range 20,000-60,000 K. Simultaneous estimates of surface gravity yield a mean gravity o…
Interstellar Abundances in Dense, Moderately Reddened Lines of Sight. I. Observational Evidence for Density-dependent Depletion
Joseph, Charles L.; Crutcher, Richard M.; Snow, Theodore P., Jr. +1 more
The nature of dust-gas interactions, which are capable of modifying the size distribution of interstellar grains and thus causing changes in the selective extinction curve, are investigated through depletion studies. The gaseous abundances of 15 elements have been determined for several lines of sight toward moderately reddened stars, each having …
EXOSAT Observations of V471 Tauri: A 9.25 Minute White Dwarf Pulsation and Orbital Phase Dependent X-Ray Dips
Sion, E. M.; Guinan, E. F.; Swank, J. H. +3 more
New results obtained from a 28 hr continuous observation of V471 Tauri with the EXOSAT satellite are reported. The detection of soft X-ray fluxes from both the white dwarf and the K dwarf, the discovery of a 9.25 minute pulsation from the white dwarf, and the discovery of orbital phase-related soft X-ray dips are discussed. The dips may be correla…
Near-simultaneous Ultraviolet and Optical Spectrophotometry of T Tauri Stars
Goodrich, Robert W.; Herbig, G. H.
A set of near-simultaneous ultraviolet and optical spectra and UBVR(J)I(J) photometry of five T Tauri stars has been analyzed for the shape of the energy distribution shortward of 3000 A. The far-ultraviolet continua of these stars are very much stronger than the level of light scattered from longer wavelengths in the IUE spectrograph. The results…
Activity in F Stars
Simon, Theodore; Boesgaard, Ann Merchant; Wolff, Sidney C.
Measurements of He I 5876 A and IUE measurements of chromospheric and transition region lines in a large sample of F-type stars are presented. The data show that activity is detectable in nearly all early F-type stars and differs in several of its characteristics from that typically seen in cooler stars with slow rotation and fully developed conve…
The Discovery of 3.9 Hour Periodic Dips in the X-Ray Intensity of XB 1254-690
Parmar, A. N.; Pakull, M.; Courvoisier, T. J. -L. +1 more
The low-mass X-ray binary XB 1254 - 690 has been discovered to show irregular dips in X-ray intensity that recur with a period of 3.9 hr consistent with the optical period derived independently. The spectral changes observed during dipping are complex and can be successfully described using a two-component model. One of these components may be X-r…