Asteroseismological Constraints on the Structure of the ZZ Ceti Stars G117-B15A and R548

Details Asteroseismological Constraints on the Structure of the ZZ Ceti Stars G117-B15A and R548 Asteroseismological Constraints on the Structure of the ZZ Ceti Stars G117-B15A and R548

Jun 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apjs..116..307b&link_type=abstract

Astrophysical Journal Supplement v.116, p.307

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51

Stars: Evolution, Stars: Individual Alphanumeric: G117-B15A, Stars: Individual Constellation Name: Zz Ceti, Stars: Variables: Other (Zz Ceti), Stars: Oscillations, Stars: White Dwarfs

Scientific paper

This study compares the theoretical pulsation periods from a new grid of evolutionary DA white dwarf models to the observed periods of the ZZ Ceti white dwarfs G117-B15A and R548 (=ZZ Ceti) in order to constrain their internal structure. Assuming that the similar periods of the two stars is the result of their having nearly identical internal structures, then they must have a hydrogen layer mass of ~10-7M* or greater. If we follow Clemens's work and identify the period near 215 s as the l=1 , k = 2 mode, then the hydrogen layer mass is close to 10-4M*, quite close to the maximum hydrogen layer mass allowed by stellar evolution theory. Based on this analysis, G117-B15A and R548 probably have masses near 0.60 M&sun; and MH ~ 10-4M*, and R548 is about 0.04 M&sun; less massive than G117-B15A. Alternatively, if 215 s is the k = 1 mode, then the hydrogen layer mass decreases to about 10-7M*, but the stellar mass remains near 0.60 M&sun;. In all cases, the helium layer mass is near 10-2M*, and the C/O core of both stars is oxygen rich. The existence of the 304 s mode of G117-B15A strongly restricts the allowable core structure. At 0.60 M&sun;, the core is either 50:50 C/O to 0.75M* or 20:80 C/O to 0.83M*. The fine-structure splitting of R548 is due to slow rotation, and we can duplicate the observed splitting trend and periods if the 213 s mode is k = 2, the model mass is near 0.54 M&sun;, and the hydrogen layer mass is near 1.5 x 10-4M*.

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