Evidence of thin helium envelopes in PG1159 stars

Abstract

We present evidence that PG1159 stars could harbour 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 PG1159 regime. Our findings are particularly interesting in view of the suggestion of an evolutionary link between the helium--deficient PG1159 star H1504+65 and the recently discovered white dwarfs with almost pure carbon atmospheres.

4 pages, 2 figures. To be published as a Letter in ApJ

References in corpus (10)

• Rare White dwarf stars with carbon atmospheres
• Asteroseismic inferences on GW Vir variable stars in the frame of new PG 1159 evolutionary models
• New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited
• Fe emission and ionized excess absorption in the luminous quasar 3C109 with XMM-Newton
• The pulsation modes of the pre-white dwarf PG 1159-035
• Asteroseismological measurements on PG 1159-035, the prototype of the GW Vir variable stars
• Asteroseismological constraints on the pulsating planetary nebula nucleus (PG1159-type) RX J2117.1+3412
• The born again (VLTP) scenario revisited: The mass of the remnants and implications for V4334 Sgr
• Asteroseismological constraints on the coolest GW Vir variable star (PG 1159-type)PG 0122+200
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Cited by in corpus (5)

• Pulsating White Dwarf Stars and Precision Asteroseismology
• The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035
• On the formation of hot DQ white dwarfs
• On the possible existence of short-period g-mode instabilities powered by nuclear burning shells in post-AGB H-deficient (PG1159-type) stars
• On the origin of white dwarfs with carbon-dominated atmospheres: the case of H1504+65