Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jrasc..99r.145w&link_type=abstract
Journal of the Royal Astronomical Society of Canada, Vol. 99, No. 4, p.145
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the discovery of spectroscopic variations in GD 323, the prototypical DAB white dwarf. Simultaneous optical spectroscopic observations over five consecutive nights of GD 323 are used to reveal quasi-periodic variations in both the hydrogen and helium absorption lines over a timescale of hours. The amplitude of the variation of the equivalent width of Hα is ~ 30%. Moreover, the strength of the hydrogen lines is shown to vary in opposite phase from that of He i .4471. These results suggest that the model currently thought to be the most viable to account for the simultaneous presence of hydrogen and helium lines in GD 323, namely a static stratified atmosphere, may need to be reexamined. Instead, a model with an inhomogeneous surface composition, resulting perhaps from the dilution of a thin hydrogen atmosphere with the underlying helium convection zone, may be a better representation of GD 323. The observed variation timescale of ~ 3.5 hours is consistent with the slow rotation rate of white-dwarf stars.
Bergeron Pierre
Pereira Carl
Wesemael François
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