Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994mnras.270..516b&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. 270, NO. 3/OCT1, P. 516, 1994
Astronomy and Astrophysics
Astronomy
14
Scientific paper
The main-sequence stars HR 8210 (1K Peg) and HD 15638 have both been found to have DA white dwarf companions by observations with the lUE satellite, following their discovery as bright EUV sources by the ROSA T Wide Field Camera. Accurate estimates of the temperature and surface gravity of each white dwarf, based on the lUE data, were oniy possible when external constraints such as the distance to the primary were applied. We present Extreme Ultraviolet Explorer observations of each of these systems. From the resulting spectra we are able to measure the temperature and surface gravity of each white dwarf with much greater accuracy than possible with the earlier data. We demonstrate that the white dwarf atmospheres have H layers sufficiently thick that they appear as pure H DAs. There is no direct evidence for the presence of any additional material in the photo spheres that might have come from interactions with the primaries. However, an inconsistency between the temperature of the HD 15638 white dwarf obtained from the EUVE spectrum, with a pure H model atmosphere, and that derived from the UV data might be explained by very small traces of heavy-element pollution. The distance we estimate for the white dwarf in HR 8210 is consistent with that to the A star, indicating that the A star has not departed from single-star evolution, nor has it evolved away from the main sequence. Measurements of the interstellar column densities yield He i/H I ratios consistent with cosmic abundances. Key words: stars: atmospheres - binaries: general - stars: individual: HD 15638 - stars: individual: HR 8210 - white dwarfs - ultraviolet: stars.
Barstow Martin Adrian
Holberg Jay Brian
Koester Detlev
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