Search Publications
Serendipitous EXOSAT sources in the region of the Coma cluster : active galactic nuclei with steep X-ray spectra.
Branduardi-Raymont, G.; Mason, K. O.; Martin, C. +1 more
A ≡7-hr observation of the central part of the Coma cluster of galaxies has been performed with the EXOSAT LE telescopes and CMA detectors. Five serendipitous sources are detected within the inner 35 arcmin radius of the field. Optical spectroscopy shows that four of these are background AGN not associated with the cluster. At the sensitivity leve…
The intrinsic ultraviolet continua of O stars.
Savage, B. D.; Massa, D.
Low-resolution IUE spectra of O and B stars in open clusters have been obtained. The main-sequence B stars are used to derive UV extinction curves for the program clusters, and these curves are used to determine the intrinsic UV to visual colors of O stars in NGC 2244, Trumpler 14, and NGC 6231. These data are analyzed in conjunction with the dere…
Detection of a compact companion of the mild barium star ksi1 Ceti.
Johnson, H. R.; Bohm-Vitense, E.
In the present paper, the observation of a white dwarf companion of the mild Ba star Xi-1 Ceti (= 65 Ceti = HR 649 = HD 13611) is reported, taking into account also the properties of the mild Ba star and of its companion. The UV spectrum of Xi-1 Ceti is discussed along with an interpretation of this spectrum. Attention is given to the effective te…
Dwarf novae in outburst : simultaneous ultraviolet and optical observations of RU Pegasi and TZ Persei.
Verbunt, F.; Schwarzenberg-Czerny, A.; Jones, D. H. P. +6 more
The authors present ultraviolet and optical observations of the dwarf novae RU Peg and TZ Per during decline from outburst. In both systems the flux drops simultaneously at all wavelengths. In TZ Per the flux distributions during standstill and during the decline from different outbursts are similar. The authors discuss briefly the implications of…
Abundance analysis from the UV spectrum of the He-w star HR 6000.
Hack, M.; Castelli, F.; Morossi, C. +1 more
A high resolution spectrum of the He-w star HR 6000, covering the SW and LW regions, has been analyzed. A fully line-blanketed model atmosphere with parameters T(e) = 14,000 K, log g = 4, microturbulence xi = 2 km/s has been adopted. This model is in agreement with the photometric data and yields the same abundance for the Fe II and Fe III ions. B…
On the ultraviolet iron spectrum of pre-white dwarfs.
Drilling, J. S.; Schoenberner, D.
The authors have detected numerous lines of Fe V, Fe VI, and Fe VII in high-resolution IUE spectra of two central stars and a number of very hot subdwarfs. The strengths of these lines vary widely from star to star, suggesting that the abundance of iron in the atmospheres of the immediate progenitors of white dwarfs in strongly variable. A possibl…
KPD 0005+5106 : a post-PG 1159 type object ?
Margon, B.; Downes, R. A.; Liebert, J.
In a survey for galactic plane UV-excess objects, a very hot (T about 100,000 K) helium-rich white dwarf is discovered. The object is spectroscopically similar to the pulsating PG 1159 class of stars, with narrow emission lines of He II, probably C IV, and possibly C III/N III, although there is no trace of carbon absorptions. Not all features hav…
A search for diffuse interstellar bands in the ultraviolet.
Snow, T. P., Jr.; Seab, C. G.
The International Ultraviolet Explorer (IUE) Satellite was used to collect interstellar extinction curves for 58 moderately reddened lines of sight. Spectral types of the background stars ranged from O7 to A0. All luminosity classes are represented, but early B main-sequence stars predominate. E(B-V) reddening values ranged from 0.14 to 1.13 mag, …
IUE and optical spectral scans of U Sagittae : an analysis and comparison with U Cephei.
Plavec, M. J.; Dobias, J. J.
Recent optical and ultraviolet observations of U Sge are presented, and the results are compared with observations of U Cephei. The observations were carried out with: the International Ultraviolet Explorer (IUE) satellite; with the ITS scanner of the Lick Observatory; and with a Varo image-tube camera attached to a coude spectrograph. Comparison …
X-Ray Spectral Variability of 3C273
Molteni, D.; Staubert, R.; Turner, M. J. L. +2 more
3C273 has been monitored by EXOSAT over the period December 1983 to June 1984 in 4 observations. In the December observation the flux was high and the spectrum showed a power law index of 1.5 changing to 0.9 at∼8 keV. In subsequent observations the flux dropped to∼40% of its original value and the hard tail disappeared. In the last observation the…