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See detailThe neon content of nearby B-type stars and its implications for the solar model problem
Morel, Thierry ULg; Butler, K.

in Astronomy and Astrophysics (2008), 487

The recent downward revision of the solar photospheric abundances now leads to severe inconsistencies between the theoretical predictions for the internal structure of the Sun and the results of ... [more ▼]

The recent downward revision of the solar photospheric abundances now leads to severe inconsistencies between the theoretical predictions for the internal structure of the Sun and the results of helioseismology. There have been claims that the solar neon abundance may be underestimated and that an increase in this poorly-known quantity could alleviate (or even completely solve) this problem. Early-type stars in the solar neighbourhood are well-suited to testing this hypothesis because they are the only stellar objects whose absolute neon abundance can be derived from the direct analysis of photospheric lines. Here we present a fully homogeneous NLTE abundance study of the optical Ne I and Ne II lines in a sample of 18 nearby, early B-type stars, which suggests log É (Ne) = 7.97 ± 0.07 dex (on the scale in which log É [H] = 12) for the present-day neon abundance of the local interstellar medium (ISM). Chemical evolution models of the Galaxy only predict a very small enrichment of the nearby interstellar gas in neon over the past 4.6 Gyr, implying that our estimate should be representative of the Sun at birth. Although higher by about 35% than the new recommended solar abundance, such a value appears insufficient by itself to restore the past agreement between the solar models and the helioseismological constraints. Appendices A and B are only available in electronic form at http://www.aanda.org Table [see full text] is also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/487/307 [less ▲]

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See detailNitrogen excess in slowly-rotating beta Cephei stars: deep mixing or diffusion?
Morel, Thierry ULg; Butler, K.; Aerts, C. et al

in Communications in Asteroseismology (2007), 150

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of ... [more ▼]

We present the results of an NLTE abundance study of a small sample of β Cephei stars, which point to the existence of a population of slowly-rotating B-type pulsators exhibiting a significant amount of nitrogen-enriched material at their surface. Although the origin of this nitrogen excess remains unclear, an overabundance preferentially occurring in stars with a detected magnetic field seems to emerge at this stage. Full details can be found in Morel et al. (2006). [less ▲]

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See detailAbundance analysis of prime B-type targets for asteroseismology. I. Nitrogen excess in slowly-rotating beta Cephei stars
Morel, Thierry ULg; Butler, K.; Aerts, C. et al

in Astronomy and Astrophysics (2006), 457

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 ... [more ▼]

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. [less ▲]

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