Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992hst..prop.3447k&link_type=abstract
HST Proposal ID #3447
Computer Science
Hst Proposal Id #3447
Scientific paper
ZZ Ceti stars are variable white dwarfs of spectral type DA. The theoretically predicted instability strip depends on several uncertain assumptions, most importantly the efficiency of convective energy transport and the detailed structure of the outer stellar layers (chemical stratification, thickness of hydrogen layers). Empirical determinations are so far not as accurate as desirable for a comparison, because: (i) the Balmer lines in the optical region reach maximum strengths within the instability strip and therefore vary only little with temperature, and (ii) the use of the ultraviolet spectrum, which is dominated by the line wing of Lyman alpha with quasimolecular satellites at 1400 and 1600 A has been hampered by the lack of an adequate theoretical description of the line shape. This theory has now been developed by one of us (N.Allard) and incorporated into stellar atmosphere programs, allowing us to determine effective temperatures in this range with an accuracy of 200 K or better. As a pilot study we have selected the apparently hottest ZZ Ceti object (G117-B15A) to demonstrate this accuracy and at the same time get a good estimate for the blue edge of the instability region.
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