Evidence of thin helium envelopes in PG 1159 stars

• Autor(a) principal: Althaus, Leandro Gabriel
• Data de Publicação: 2008
• Outros Autores: Córsico, Alejandro Hugo, Bertolami, Marcelo Miguel Miller, García-Berro, Enrique, Kepler, Souza Oliveira
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFRGS
• Texto Completo: http://hdl.handle.net/10183/108966
• topic: Evolucao estelar; Interior estelar; Anãs brancas; Atmosferas estelares; Matéria circumestelar; Hélio; Dense matter; Diffusion; Stars: abundances; Stars: evolution; Stars: interiors; White dwarfs

We present evidence that PG 1159 stars could harbor He-rich envelopes substantially thinner than those predicted by current evolutionary models with current estimates of mass loss, which may be attributable to an extensive mass-loss episode during the born-again AGB phase. Specifically, we show that the models with thin He-rich envelopes predict remarkably large magnitudes of the rates of period change of the trapped and untrapped modes observed in the pulsating star PG 1159−035. This is a consequence of the much shorter evolutionary timescale of the models with thin He-rich envelopes during the low-gravity PG 1159 regime. Our findings are particularly interesting in view of the suggestion of an evolutionary link between the helium-deficient PG 1159 star H1504+65 and the recently discovered white dwarfs with almost pure carbon atmospheres.