Full evolutionary models for PG 1159 stars. Implications for the helium-rich O(He) stars

Abstract

Aims. We present full evolutionary calculations appropriate to post-AGB PG 1159 stars for a wide range of stellar masses. Methods. We take into account the complete evolutionary stages of PG 1159 progenitors starting from the Zero Age Main Sequence. We consider the two kinds of Born Again Scenarios, the very late thermal pulse (VLTP) and the late thermal pulse (LTP), that give rise to hydrogen-deficient compositions. The location of our PG 1159 tracks in the effective temperature-gravity diagram and their comparison with previous calculations as well as the resulting surface compositions are discussed. Results. Our results reinforce the idea that the different abundances of 14 N observed at the surface of those PG 1159 stars with undetected hydrogen is an indication that the progenitors of these stars would have evolved through a VLTP episode, where most of the hydrogen content of the remnant is burnt, or LTP, where hydrogen is not burnt but instead diluted to very low surface abundances. We derive new values for spectroscopical masses based on these models. We discuss the correlation between the presence of planetary nebulae and the 14 N abundance as another indicator that 14 N-rich objects should come from a VLTP episode while 14 N-deficient ones should be the result of a LTP. Finally, we discuss an evolutionary scenario that could explain the existence of PG 1159 stars with unusually high helium abundances and a possible evolutionary connection between these stars and the low mass O(He) stars.

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

“…Their post-AGB evolution is extremely slow with the 0.546 M track (Schönberner 1983) taking 3 × 10 5 yr to reach a peak temperature. The stars of Table 2 are all PG1159 stars, A48, page 4 of 27 which are hydrogen-poor and believed to have undergone a late thermal pulse during the post-AGB evolution (Miller Bertolami & Althaus 2006). Their current evolution therefore differs from that of the hydrogen-burning tracks considered here.…”

Stellar wind models of subluminous hot stars

“…There are more possible evolutionary channels that lead to different types of subluminous objects. Helium low-luminosity stars may originate as a merger of two white dwarfs (Iben & Tutukov 1984;Saio & Jeffery 2000;Zhang & Jeffery 2012) or in a late thermal pulse (Iben et al 1983;Miller Bertolami & Althaus 2006). Subluminous stars may be also products of red giants, which were stripped off their envelopes possibly during binary evolution (e.g., Han et al 2007).…”

Asteroseismological analysis of the GW Virginis stars SDSS J0349-0059 and VV 47

“…For the case of VV 47, as seen in Figure 3, there is no unambiguous asteroseismological solution, not even within the range of allowed T eff . Finally, there is another mass determination for the two stars under analysis we obtained using the spectroscopic data given by [4] and [7] combined with our grid of models ( [5]). It results in M * = 0.543M for J0349 and M * = 0.529M for VV 47 (average value).…”

“…Given the large uncertainty in the T eff , this star may be evolving either before or after the "evolutionary knee". We computed adiabatic nonradial g-mode pulsation periods on PG 1159 evolutionary models with stellar masses between 0.515 and 0.741 M that take into account the complete evolution of the progenitor stars through the thermally pulsing AGB phase and born-again episode (that explains their H deficiency; [1,2,5]). …”