NLTE Spectral Analysis of the Pre White Dwarf PG1159-035

Details NLTE Spectral Analysis of the Pre White Dwarf PG1159-035 NLTE Spectral Analysis of the Pre White Dwarf PG1159-035

Jul 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991hst..prop.2741h&link_type=abstract

HST Proposal ID #2741

Computer Science

Hst Proposal Id #2741

Scientific paper

PG1159-035 is the prototype of a new class of hydrogen-deficient pre white dwarfs (PWD) representing the hottest episode (Teff.GE.100,000K) of PWD-evolution. It also shows low-amplitude multi-periodic variations which have been identified as non-radial g-mode pulsations. Because of these properties, PG1159-035 is a rosetta stone for our understanding of the late phase of stellar evolution. Modelling of the pulsations not only allows the stellar mass to be determind but also the internal structure to be probed. However, the position of PG1159-035 in the HR diagram and its chemical surface composition are a prerequisite for the pulsational models as well as for the discussion of its evolutionary status. Due to the lack of adequate model atmospheres, these basic atmospheric parameters have not yet been determined. To construct such models is a challenging problem because non-LTE effects are large and a very peculiar composition (He-, C- and O-rich) has to be accounted for. Since available model atmosphere techniques fail, we have developed a new computer code based on operator perturbation techniques which gave way to a new generation of highly sophisticated non-LTE model atmospheres. Proposed HST spectroscopy of crucial UV lines will allow the basic atmospheric parameters to be determined with high precision. These will set important constraints to be met by pulsational and evolutionary models.

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