Spectroscopy of the W Virginis star V1 (K 307 ) in the globular cluster M12

Details Spectroscopy of the W Virginis star V1 (K 307 ) in the globular cluster M12 Spectroscopy of the W Virginis star V1 (K 307 ) in the globular cluster M12

Nov 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003astl...29..748k&link_type=abstract

Astronomy Letters, Volume 29, Issue 11, pp.748-762

Astronomy and Astrophysics

Astronomy

3

Globular Clusters, Post-Agb Stars, Spectroscopy, Chemical Composition, Shock Waves

Scientific paper

High-resolution CCD spectra have been obtained for the first time for the W Virginis star V1 (K 307) in the globular cluster M12 and its closest neighbor K 307b ( m pg=14m; the angular distance from the W Vir star is δ<1 arcsec). We determined the fundamental parameters ( T eff=5600 K, log g=1.3, and T eff=4200 K, log g=1.0 for the W Vir star and the neighboring star, respectively) and their detailed chemical composition. The derived metallicities of the two stars ([Fe/H]=-1.27 and -1.22 relative to the solar value) are in good agreement with the metallicities of other cluster members. Changed CNO abundances were found in the atmosphere of the W Vir star: a small carbon overabundance, [C/Fe]=+0.30 dex, and a large nitrogen overabundance, [N/Fe]=+1.15 dex, with oxygen being underabundant, [O/Fe]≈-0.2 dex. The C/O ratio is ≥1. Na and the α-process elements Mg, Al, Si, Ca, and Ti are variously enhanced with respect to iron. We found an enhanced abundance of s-process metals relative to iron: [X/Fe]=+0.34 for Y, Zr, and Ba. The overabundance of the heavier metals La, Ce, and Nd with respect to iron is larger: [X/Fe]=+0.49. The largest overabundance was found for the r-process element europium, [Eu/Fe]=+0.82. The spectrum of the W Vir star exhibits the Hα and Hβ absorption-emission profiles and the He I λ5876 Å emission line, which are traditionally interpreted as a result of shock passage in the atmosphere. However, the radial velocities determined from absorption and emission features are in conflict with the formation pattern of a strong shock. The high luminosity log L/ L &sun; = 2.98, the chemica peculiarities, and the spectral peculiarity are consistent with the post-AGB evolution in the instability strip. The pattern of relative elemental abundances [X/Fe]in the atmosphere of the neighboring star K 307b is solar. Statistically significant differences were found only for sodium and α-process elements: the mean overabundance of light metals is [X/Fe]=+0.35.

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