On the possible existence of short-period g-mode instabilities powered by nuclear burning shells in post-AGB H-deficient (PG1159-type) stars

Abstract

We present a pulsational stability analysis of hot post-AGB H-deficient pre-white dwarf stars with active He-burning shells. The stellar models employed are state-of-the-art equilibrium structures representative of PG1159 stars derived from the complete evolution of the progenitor stars. On the basis of fully nonadiabatic pulsation computations, we confirmed theoretical evidence for the existence of a separate PG1159 instability strip in the $\log T_{\mathrm{eff}}-\log g$ diagram characterized by short-period $g$-modes excited by the $\epsilon$-mechanism. This instability strip partially overlaps the already known GW Vir instability strip of intermediate/long period $g$-modes destabilized by the classical $\kappa$-mechanism acting on the partial ionization of C and/or O in the envelope of PG1159 stars. We found that PG1159 stars characterized by thick He-rich envelopes and located inside this overlapping region could exhibit both short and intermediate/long periods simultaneously. we study the particular case of VV 47, a pulsating planetary nebula nucleus that has been reported to exhibit a series of unusually short pulsation periods. We found that the long periods exhibited by VV 47 can be readily explained by the classical $\kappa$-mechanism, while the observed short-period branch below $\approx 300$ s could correspond to modes triggered by the He-burning shell through the $\epsilon$-mechanism, although more observational work is needed to confirm the reality of these short-period modes. Were the existence of short-period $g$-modes in this star convincingly confirmed by future observations, VV 47 could be the first known pulsating star in which both the $\kappa$-mechanism and the $\epsilon$-mechanism of mode driving are simultaneously operating.

9 pages, 5 figures, 2 tables. To be published in The Astrophysical Journal

References in corpus (7)

• Pulsating White Dwarf Stars and Precision Asteroseismology
• New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited
• 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
• The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035
• The Current Status of Asteroseismology
• Evidence of thin helium envelopes in PG1159 stars

Cited by in corpus (6)

• Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS: I. Asteroseismology of the GW Vir stars RX J2117+3412, HS 2324+3944, NGC 6905, NGC 1501, NGC 2371, and K 1-16
• Short-period $g$-mode pulsations in low-mass white dwarfs triggered by H shell burning
• Pulsations of Pre-White Dwarfs with Hydrogen-dominated Atmospheres
• The Missing Link? Discovery of Pulsations in the Nitrogen-rich PG 1159 Star PG 1144+005
• Exploring the internal rotation of the extremely low-mass He-core white dwarf GD 278 with TESS asteroseismology
• A new instability domain of CNO-flashing low-mass He-core stars on their early white-dwarf cooling branches