TY  - JOUR
A1  - Sander, Andreas Alexander Christoph
A1  - Todt, Helge Tobias
A1  - Hainich, Rainer
A1  - Hamann, Wolf-Rainer
T1  - The Wolf-Rayet stars in M31 I. Analysis of the late-type WN stars
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M 31 will extend our understanding of these objects in different galactic environments.
 Aims. The present study aims at the late-type WN stars in M 31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M 31.
 Methods. We used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN I 0 and WN I I subtypes, our WN models have been extended into this temperature regime.
 Results. Stellar and atmospheric parameters are derived for all known late-type WN stars in M 31 with available spectra. All of these stars still have hydrogen in their outer envelopes, some of them up to 50% by mass. The stars are located on the cool side of the zero age main sequence in the Hertzsprung-Russell diagram, while their luminosities range from 105 to 1064). It is remarkable that no star exceeds 106 L.
 Conclusions. If formed via single-star evolution, the late-type WN stars in M 31 stem from an initial mass range between 20 and 60 M-circle dot. From the very late-type WN9-11 stars, only one star is located in the S Doradus instability strip. We do not find any late-type WN stars with the high luminosities known in the Milky Way.
KW  - stars: massive
KW  - stars: evolution
KW  - stars: mass-loss
KW  - stars: Wolf-Rayet
KW  - stars: atmospheres
KW  - stars: winds
KW  - outflows
Y1  - 2014
U6  - https://doi.org/10.1051/0004-6361/201323240
SN  - 0004-6361
SN  - 1432-0746
VL  - 563
PB  - EDP Sciences
CY  - Les Ulis
ER  -