Hot White Dwarfs in the Extreme Ultraviolet Explorer Survey. I. Properties of a Southern Hemisphere Sample

1996 ◽  
Vol 467 ◽  
pp. 782 ◽  
Author(s):  
Stephane Vennes ◽  
Peter A. Thejll ◽  
Dayal T. Wickramasinghe ◽  
Michael S. Bessell
1996 ◽  
Vol 152 ◽  
pp. 217-222
Author(s):  
Jean Dupuis ◽  
Stéphane Vennes

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.


1990 ◽  
Vol 115 ◽  
pp. 335-338
Author(s):  
J. V. Vallerga ◽  
P. Jelinsky ◽  
P. W. Vedder ◽  
R. F. Malina

AbstractThe expected in-orbit performance of the three spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite is presented. Recent calibrations of the gratings, mirrors and detectors using monochromatic and continuum EUV light sources allow the calculation of the spectral resolution and throughput of the instrument. An effective area range of 0.2 to 2.8 cm2 is achieved over the wavelength range 70-600Å with a peak spectral resolution λ/Δλ (FWHM) of ~ 360 assuming a spacecraft pointing knowledge of 10 arc seconds (FWHM). For a 40,000 sec observation, the average 3σ sensitivity to a monochromatic line source is 3 × 103 photons cm-2 sec-1. Simulated observations of known classes of EUV sources such as hot white dwarfs and cataclysmic variables are also presented.


1999 ◽  
Vol 517 (1) ◽  
pp. 399-415 ◽  
Author(s):  
R. Napiwotzki ◽  
Paul J. Green ◽  
Rex A. Saffer

1996 ◽  
Vol 152 ◽  
pp. 381-388
Author(s):  
Ivan Hubeny ◽  
Thierry Lanz

The only stars other than white dwarfs whose photospheric extreme ultraviolet radiation has been detected are ϵ and β CMa. It is therefore of considerable theoretical interest to compare the EUVE observations of these two giant B stars to predicted spectra. However, both LTE and non-LTE very sophisticated line blanketed model atmospheres fail to match the observed flux. This failure leaves the stellar photosphere theory, even for seemingly “simple” objects as normal B giants were believed to be, in a rather dubious position. This paper briefly summarizes possible reasons for the failure of existing models to describe the EUVE observations of hot stars. In particular, we discuss the effects of uncertainties in the line blanketing, and the effects of the photosphere-wind interaction.


1976 ◽  
Vol 205 ◽  
pp. 426 ◽  
Author(s):  
P. Henry ◽  
S. Bowyer ◽  
M. Lampton ◽  
F. Paresce ◽  
R. Cruddace

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