IUE observations of a hot DAO white dwarf: Implications for diffusion theory and photospheric stratification

Details IUE observations of a hot DAO white dwarf: Implications for diffusion theory and photospheric stratification IUE observations of a hot DAO white dwarf: Implications for diffusion theory and photospheric stratification

Jun 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988esasp.281a.263h&link_type=abstract

In ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1 p 263-265 (SEE N89-10682 01-89)

Astronomy and Astrophysics

Astronomy

4

Atmospheric Stratification, Diffusion Theory, Iue, Photosphere, Spaceborne Astronomy, Stellar Atmospheres, Ultraviolet Astronomy, Ultraviolet Spectra, White Dwarf Stars, H Alpha Line, Lyman Alpha Radiation, Stellar Temperature

Scientific paper

Observations of the DAO white dwarf PG1210+533, including the first high dispersion spectrum of a hybrid H-He object of this nature were obtained by IUE. In contrast with hot DAs in the 50,000 K temperature range, PG1210+533 shows no narrow interstellar-like metal lines, in spite of an optically observed He/H abundance of 0.1. This lack of metal makes accretion from the ISM an unlikely source for the He in the PG1210+533 photosphere. A significant discovery in the high dispersion spectrum is the existence of a sharp, non-LTE like, core seen in the He II 1640 line. Such features are detected in DO white dwarfs. A small aperture SWP low dispersion observation reveals the Lyman alpha profile of PG1210+533 to be surprisingly weak and narrow. Fits of this profile using pure H models yielded a T(eff) = 56,000 K. Fits of the Balmer H gamma profile however, yield T(eff) = 42,300 K and log g = 8.5 + or - 0.5 for the same models. It is unlikely that homogeneously mixed H-He atmospheres can resolve the inconsistency between the Lyman alpha and H gamma features in this star. Stratified models involving thin H photospheres may be necessary to explain these results.

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