Volume 423, Number 1, August III 2004
|Page(s)||353 - 362|
|Published online||29 July 2004|
Chemical composition and evolutionary status of nine UV-bright stars in five globular clusters from VLT/UVES spectra *,**,***
UMR 5024 CNRS/UMII, Université Montpellier II, CC 72, 34095 Montpellier Cedex 5, France e-mail: Gerard.Jasniewicz@graal.univ-montp2.fr
2 Dpt. Cassiopée, UMR 6202, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
3 Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
Accepted: 17 April 2004
We have derived the chemical composition of nine UV-bright stars belonging to five Galactic globular clusters of various metallicities ([Fe/H] from -1.0 to -2.4 dex). The analyses are based on high resolution spectra obtained with the UV-Visual Echelle Spectrograph (UVES) at VLT-UT2. The evolutionary status of the stars is assessed from the chemical analysis and location in the H-R diagram. The star ID7 in NGC 5986 is confirmed as a bona fide post-asymptotic giant branch star (post-AGB) whereas the high-luminosity star ID6 has probably left the AGB before the third dredge-up. ZNG 1 in NGC 6712 shows an overabundance of sodium, oxygen, and silicon similar to overabundances we find in the UV-bright star ID6 in NGC 5986; both stars could be in a post-early-AGB (PEAGB) phase of evolution. The UV-bright star ZNG 7 in NGC 6218 seems to be an AGB star. The stars V-4 and ZNG 5 in NGC 6656 are in a post-horizontal-branch phase of evolution, with V-4 being significantly overabundant in heavy elements. The origin of these overabundances is discussed in the context of the evolutionary versus primordial scenario. The three UV-bright stars K 260, K 996 and K 1082 observed in the very metal-deficient globular cluster NGC 7078 are post-horizontal-branch stars, one of them being slightly enriched in s-elements but with a luminosity too low for third dredge-up to have occured. The abundance patterns of K 1082 in NGC 7078 seem to indicate the presence of mild diffusion and a radiative levitation process, already reported in the blue HB stars of M 13 (Behr et al. [CITE], ApJ, 517, L135) and NGC 6752 (Moehler et al. [CITE], A&A, 339, 537).
Key words: stars: abundances / stars : AGB and post-AGB / Galaxy: globular clusters : general
Full Table [see full text] is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/353
© ESO, 2004
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