2007A&A...467.1175A


Query : 2007A&A...467.1175A

2007A&A...467.1175A - Astronomy and Astrophysics, volume 467, 1175-1180 (2007/6-1)

Low-mass, helium-enriched PG 1159 stars: a possible evolutionary origin and implications for their pulsational stability properties.

ALTHAUS L.G., CORSICO A.H. and MILLER BERTOLAMI M.M.

Abstract (from CDS):

We examine a recently-proposed evolutionary scenario that could explain the existence of the low-mass, helium-enriched PG 1159 stars. We focus in particular on studying the pulsational stability properties of the evolutionary models predicted by such a scenario. We assess the overstability of pulsation g-modes of stellar models as evolution proceeds in the PG 1159 domain. Stellar models are extracted from the full evolution of a 1-M model star that experiences its first thermal pulse as a late thermal pulse (LTP) after leaving the AGB. The evolutionary stages corresponding to the born-again episode and the subsequent helium sub-flashes are taken into account in detail. Under reasonable assumptions of mass-loss rate, the evolutionary scenario reproduces the high helium abundances observed in some PG 1159 stars. We find that, despite the high helium abundance in the driving layers, a narrow region exists in the logTeff-logg diagram for which the helium-enriched PG 1159 sequence exhibits unstable pulsation modes with periods in the range 500 to 1600 s. In particular, the nonpulsating helium-enriched PG 1159 star, MCT 0130-1937, is located outside the theoretical instability domain. Our results suggest that MCT 0130-1937 is a real non-pulsating star and that the lack of pulsations should not be attributed to unfavorable geometry. Our study hints at a consistent picture between the evolutionary scenario that could explain the existence of helium-enriched PG 1159 stars and the nonvariable nature of MCT 0130-1937. We also present theoretical support for the unusually high helium abundance observed in the nonpulsating PG 1159 star HS 1517+7403. We suggest that HS 1517+7403could be a transition object linking the low-mass helium-rich O(He) stars with the helium-enriched PG 1159 stars via the evolutionary connection K1-27 -> HS 1517+7403 -> MCT 0130-1937.

Abstract Copyright:

Journal keyword(s): stars: evolution - stars: abundances - stars: AGB and post-AGB - stars: interiors - stars: variables: general - white dwarfs

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 GD 1088 ** 01 32 39.347 -19 21 40.38   15.51 15.77 15.77   PG1159 45 0
2 PN K 1-27 PN 05 57 02.1748457640 -75 40 22.478040120     16.04 16.27 16.41 sdOHe 83 0
3 HS 0704+6153 WD* 07 09 32.4965901360 +61 48 19.458822312   17.3   17.1   PG1159 37 0
4 V* GW Vir WD* 12 01 45.9731868264 -03 45 40.628670300   14.87 15.04     DOQZ1 475 0
5 HS 1517+7403 WD* 15 16 46.4260387056 +73 52 06.953282400   16.4   16.9   DO 39 0
6 PG 1707+427 WD* 17 08 47.6869215528 +42 41 00.558430656   16.18       PG1159 112 0
7 V* V4334 Sgr CV* 17 52 32.69352 -17 41 08.0160           F2Ia 353 0
8 V* IR Peg WD* 21 34 08.2124719240 +06 50 57.662044329   16.15       PG1159 115 0
9 HS 2209+8229 WD? 22 08 25.8763154304 +82 44 51.409027968   16.0       DO/sdO 13 0

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2022.08.10-18:33:06

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