TY  - JOUR
A1  - Löbling, Lisa
A1  - Rauch, Thomas
A1  - Bertolami Miller, Marcelo Miguel
A1  - Todt, Helge Tobias
A1  - Friederich, F.
A1  - Ziegler, M.
A1  - Werner, Klaus
A1  - Kruk, J. W.
T1  - Spectral analysis of the hybrid PG 1159-type central stars of the planetary nebulae Abell 43 and NGC7094
JF  - Monthly notices of the Royal Astronomical Society
N2  - Stellar post asymptotic giant branch (post-AGB) evolution can be completely altered by a final thermal pulse (FTP) which may occur when the star is still leaving the AGB (AFTP), at the departure from the AGB at still constant luminosity (late TP, LTP) or after the entry to the white-dwarf cooling sequence (very late TP, VLTP). Then convection mixes the Herich material with the H-rich envelope. According to stellar evolution models the result is a star with a surface composition of H approximate to 20 per cent by mass (AFTP), approximate to 1 per cent (LTP), or (almost) no H (VLTP). Since FTP stars exhibit intershell material at their surface, spectral analyses establish constraints for AGB nucleosynthesis and stellar evolution. We performed a spectral analysis of the so-called hybrid PG 1159-type central stars (CS) of the planetary nebulae Abell 43 and NGC7094 by means of non-local thermodynamical equilibrium models. We confirm the previously determined effective temperatures of T-eff = 115 000 +/- 5 000K and determine surface gravities of log (g /(cm s(-2))) = 5.6 +/- 0.1 for both. From a comparison with AFTP evolutionary tracks, we derive stellar masses of 0.57(-0.04)(+0.07)M(circle dot) and determine the abundances of H, He, and metals up to Xe. Both CS are likely AFTP stars with a surface H mass fraction of 0.25 +/- 0.03 and 0.15 +/- 0.03, respectively, and an Fe deficiency indicating subsolar initial metallicities. The light metals show typical PG 1159-type abundances and the elemental composition is in good agreement with predictions from AFTP evolutionary models. However, the expansion ages do not agree with evolution time-scales expected from the AFTP scenario and alternatives should be explored.
KW  - stars: abundances
KW  - stars: AGB and post-AGB
KW  - stars: atmospheres
KW  - stars: evolution
KW  - stars: individual: WD1751+106
KW  - stars: individual: WD2134+125
Y1  - 2019
U6  - https://doi.org/10.1093/mnras/stz1994
SN  - 0035-8711
SN  - 1365-2966
VL  - 489
IS  - 1
SP  - 1054
EP  - 1071
PB  - Oxford Univ. Press
CY  - Oxford
ER  -