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Issue A&A
Volume 378, Number 2, November I 2001
Page(s) 455 - 465
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20011210



A&A 378, 455-465 (2001)
DOI: 10.1051/0004-6361:20011210

K 413, a star near the AGB in the globular cluster M 12

V. G. Klochkova1, 2 and N. N. Samus3, 4

1  Special Astrophysical Observatory, N. Arkhyz 369167, Russia
2  Isaac Newton Institute of Chile, SAO Branch, Russia
3  Institute of Astronomy of Russian Acad. Sci., 48, Pyatnitskaya Str., Moscow 109017, Russia and Sternberg Astronomical Institute of Moscow University, 13, University Ave., Moscow 119899, Russia
4  Isaac Newton Institute of Chile, Moscow Branch, Russia

(Received 27 June 2001 / Accepted 20 August 2001 )

Abstract
CCD spectra obtained with the echelle spectrometer of the 6-meter telescope were used to determine, by the model atmospheres method, the fundamental parameters ( = 4800 K, log g = 0.7) and detailed chemical abundances for the star K 413, a member of the globular cluster M 12. The resulting value, ${\rm [Fe/H] = -1.38}$, is the first metallicity determination for M 12 using high-resolution spectra. The main characteristic feature of the star's atmospheric chemical abundance pattern is a large oxygen excess, ${\rm [O/Fe] \approx +2}$. The s-process elements are probably slightly depleted compared to metallicity: ${\rm [X/Fe] = -0.04}$ for yttrium and zirconium, ${\rm [Ba/Fe] = -0.12}$ for barium. Abundances of the heavier elements: La, Ce, Nd, and Pr, do not differ, relative to iron, from the solar ones: ${\rm [heavy/Fe] = 0.0}$. The europium excess, ${\rm [Eu/Fe] = +0.48}$, is typical of members of low-metallicity globular clusters. The spectrum of K 413 shows, for the H$\alpha$ line, an variable absorption and emission profile. From its high luminosity and chemical abundance anomalies, we can suppose that K 413 is in an evolutionary stage after the AGB. In the spectrum, we find absorption details that can be identified with diffuse interstellar bands displaced by 16 to longer wavelengths relative to the star's velocity.


Key words: globular clusters: general -- globular clusters: individual M 12 -- stars: abundances -- stars: atmospheres -- stars: AGB and post-AGB

Offprint request: V. G. Klochkova, valenta@sao.ru

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