Article (Scientific journals)
Abundance analysis of prime B-type targets for asteroseismology. I. Nitrogen excess in slowly-rotating beta Cephei stars
Morel, Thierry; Butler, K.; Aerts, C. et al.
2006In Astronomy and Astrophysics, 457, p. 651-663
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Keywords :
stars: early-type; stars: fundamental parameters; stars: abundances; stars: atmospheres; stars: oscillations
Abstract :
[en] Seismic modelling of the β Cephei stars promises major advances in our understanding of the physics of early B-type stars on (or close to) the main sequence. However, a precise knowledge of their physical parameters and metallicity is a prerequisite for correct mode identification and inferences regarding their internal structure. Here we present the results of a detailed NLTE abundance study of nine prime targets for theoretical modelling: <ASTROBJ>γ Peg</ASTROBJ>, <ASTROBJ>δ Cet</ASTROBJ>, <ASTROBJ>ν Eri</ASTROBJ>, <ASTROBJ>β CMa</ASTROBJ>, <ASTROBJ>ξ1 CMa</ASTROBJ>, <ASTROBJ>V836 Cen</ASTROBJ>, <ASTROBJ>V2052 Oph</ASTROBJ>, <ASTROBJ>β Cep</ASTROBJ> and DD (12) Lac (hereafter <ASTROBJ>12 Lac</ASTROBJ>). The following chemical elements are considered: He, C, N, O, Mg, Al, Si, S and Fe. Our curve-of-growth abundance analysis is based on a large number of time-resolved, high-resolution optical spectra covering in most cases the entire oscillation cycle of the stars. Nitrogen is found to be enhanced by up to 0.6 dex in four stars, three of which have severe constraints on their equatorial rotational velocity, Ω R, from seismic or line-profile variation studies: <ASTROBJ>β Cep</ASTROBJ> (Ω R ~ 26 km s[SUP]-1[/SUP]), <ASTROBJ>V2052 Oph</ASTROBJ> (Ω R ~ 56 km s[SUP]-1[/SUP]), <ASTROBJ>δ Cet</ASTROBJ> (Ω R < 28 km s[SUP]-1[/SUP]) and <ASTROBJ>ξ1 CMa</ASTROBJ> (Ω R sin i ⪠10 km s[SUP]-1[/SUP]). The existence of core-processed material at the surface of such largely unevolved, slowly-rotating objects is not predicted by current evolutionary models including rotation. We draw attention to the fact that three stars in this subsample have a detected magnetic field and briefly discuss recent theoretical work pointing to the occurrence of diffusion effects in β Cephei stars possibly capable of altering the nitrogen surface abundance. On the other hand, the abundances of all the other chemical elements considered are, within the errors, indistinguishable from the values found for OB dwarfs in the solar neighbourhood. Despite the mild nitrogen excess observed in some objects, we thus find no evidence for a significantly higher photospheric metal content in the studied β Cephei stars compared to non-pulsating B-type stars of similar characteristics.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Morel, Thierry  ;  Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200D, 3001 Leuven, Belgium
Butler, K.;  Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany
Aerts, C.;  Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium ; Department of Astrophysics, University of Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
Neiner, C.;  Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium ; GEPI, UMR 8111 du CNRS, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
Briquet, Maryline ;  Katholieke Universiteit Leuven, Departement Natuurkunde en Sterrenkunde, Instituut voor Sterrenkunde, Celestijnenlaan 200B, 3001 Leuven, Belgium
Language :
English
Title :
Abundance analysis of prime B-type targets for asteroseismology. I. Nitrogen excess in slowly-rotating beta Cephei stars
Publication date :
01 October 2006
Journal title :
Astronomy and Astrophysics
ISSN :
0004-6361
eISSN :
1432-0746
Publisher :
EDP Sciences, Les Ulis, France
Volume :
457
Pages :
651-663
Peer reviewed :
Peer Reviewed verified by ORBi
Commentary :
http://de.arxiv.org/abs/astro-ph/0607264
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