Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984apj...279..751b&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 279, April 15, 1984, p. 751-757. Research supported by the Donaghey Foundat
Astronomy and Astrophysics
Astronomy
45
Light Curve, Stellar Oscillations, Stellar Temperature, Ultraviolet Astronomy, Variable Stars, White Dwarf Stars, Power Spectra, Stellar Evolution, Stellar Spectra, Ubv Spectra
Scientific paper
High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.
Bond Howard E.
Grauer Albert D.
Green Richard F.
Liebert James W.
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