NLTE Spectral Analysis of PG1159 Stars: Finding the Limits of the GW VIR Instability Strip

Details NLTE Spectral Analysis of PG1159 Stars: Finding the Limits of the GW VIR Instability Strip NLTE Spectral Analysis of PG1159 Stars: Finding the Limits of the GW VIR Instability Strip

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5866h&link_type=abstract

HST Proposal ID #5866

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Hst Proposal Id #5866 Hot Stars

Scientific paper

The PG1159 stars form a new class of hydrogen deficient pre white dwarfs (PWD) representing the hottest stage of PWD evolution. Quan-titative spectral analyses of all known PG1159 stars have been carried out by the proposers from optical, UV (IUE + HST-FOS) and EUV (EUVE) observations. It has been shown that these stars have atmospheres dominated by C and He. In the hottest stars also a significant amount of O is present. About every other member of the PG1159 stars is a non-radial, multi-periodic g-mode pulsator driven by cyclic ionization of C and O. Modelling of the pulsations allows the stellar mass to be determined very accurately and the stellar interior to be probed (asteroseismology). A prerequisite for such modelling is a precise determination of the photospheric parameters. We propose to obtain UV observations of 8 PG1159 stars (4 pulsators and 4 non-pulsators) in order to trace differences in photospheric parameters and composition (especially O). The spectra will be analysed with new highly sophisticated NLTE line blanketed model atmospheres, which allow the synthetic spectrum to be calculated and line blending of iron group elements to be included self- consistently. The results will allow us to determine the position of the new instability strip (defined by the pulsating PG1159 stars) in the HRD. This is an updated version of cycle3 proposal 4263 which was awarded 9.48 hours FOS observing time (medium priority) but no observations were carried out.

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