Query : 2007A&A...461..571H

2007A&A...461..571H - Astronomy and Astrophysics, volume 461, 571-583 (2007/1-2)

Very low-metallicity massive stars. Pre-SN evolution models and primary nitrogen production.


Abstract (from CDS):

Precise measurements of the surface abundances of extremely low-metallicity stars have recently been obtained, and they provide new constraints for the stellar evolution models. Stellar evolution models were computed in order to explain the surface abundances observed, in particular of nitrogen. Two series of models were computed. The first series consists of 20M models with varying initial metallicity (Z=0.02 down to Z=10–8) and rotation (υini=0-600km/s). The second one consists of models with an initial metallicity of Z=10–8, masses between 9 and 85M, and fast initial rotation velocities (υini=600-800km/s). The most interesting models are those with Z=10–8 ([Fe/H]~-6.6). In the course of helium burning, carbon and oxygen are mixed into the hydrogen-burning shell. This boosts the importance of the shell and causes a reduction of the CO core mass. Later in the evolution, the hydrogen shell deepens and produces a large amount of primary nitrogen. For the most massive models (M>60M), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. The 85M model ends up as a WO-type Wolf-Rayet star. Therefore the models predict SNe of type Ic and possibly long and soft GRBs at very low metallicities. The rotating 20M models can best reproduce the observed CNO abundances at the surface of extremely metal-poor (EMP) stars and the metallicity trends when their angular momentum content is the same as at solar metallicity (and therefore have an increasing surface velocity with decreasing metallicity). The wind of the massive-star models can reproduce the CNO abundances of the most metal-poor carbon-rich star known to date, HE 1327-2326.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: evolution - stars: rotation - stars: mass-loss - stars: Wolf-Rayet - stars: supernovae: general

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 HE 0107-5240 Pe* 01 09 29.1555567432 -52 24 34.202039148   15.89 15.07 15.10 14.283 CEMP-no 236 0
2 G 77-61 Pe* 03 32 38.0920129269 +01 58 00.084645962   15.60 13.90 12.9   dC-J_CH5 129 0
3 HE 1327-2326 Pe* 13 30 05.9394958608 -23 41 49.699340844 13.761 14.01 13.55 13.50 12.803 CEMP-no 232 0
4 BPS CS 29498-0043 Pe* 21 03 52.1197651440 -29 42 50.344181712   14.8 13.72 13.013 12.406 CEMP-no 91 0
5 HE 2323-0256 Pe* 23 26 29.8073738880 -02 39 58.036383180   15.12 14.36   13.358 CEMP-no 175 0

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