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Astron. Astrophys. 353, 557-568 (2000)


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Heavy-element abundances in the CH/CN-strong very metal-poor stars CS 22948-27 and CS 29497-34 *

V. Hill 1,2, B. Barbuy 3, M. Spite 2, F. Spite 2, R. Cayrel 4, B. Plez 5, T.C. Beers 6, B. Nordström 7 and P.E. Nissen 8

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany (vhill@eso.org)
2 Observatoire de Paris-Meudon, DASGAL, URM 8633 du CNRS, 92195 Meudon Cedex, France (Monique.Spite, Francois.Spite@obspm.fr)
3 Universidade de São Paulo, CP 3386, São Paulo 01060-970, Brazil (barbuy@orion.iagusp.usp.br)
4 Observatoire de Paris, DASGAL, URM 8633 du CNRS, 61 Av. de l'Observatoire, 75014 Paris, France (Roger.Cayrel@obspm.fr)
5 GRAAL cc72, Université de Montpellier II, 34095 Montpellier Cedex 5, France (plez@graal.univ-montp2.fr)
6 Michigan State University, Department of Physics andtronomy, East Lansing, MI 48824, USA (beers@pa.msu.edu)
7 Niels Bohr Institute for Astronomy, Physics and Geophysics, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark (birgitta@astro.ku.dk)
8 Institute of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark (pen@obs.aau.dk)

Received 26 July 1999 / Accepted 2 November 1999

Abstract

We have carried out a new analysis of the very metal-poor CH/CN strong stars CS 22948-27 and CS 29497-34. In particular, the effective temperatures were recomputed by comparing newly obtained photometric data to colours derived from model atmospheres computed especially for these stars. Metallicities of [Fe/H] = -2.45 and -2.90 are found, respectively, for CS 22948-27 and CS 29497-34.

The abundances of heavy elements have been derived from newly obtained high-resolution spectroscopy in the blue spectral region, together with previously obtained spectra in the red, resulting in a total wavelength coverage of [FORMULA] 4000-8200 Å.

We find that the abundance patterns of our stars reflect enrichment by the r-process (as indicated by a high Eu abundance), as well as by the s-process, which could be due to a mass transfer episode from a companion crossing the AGB phase, although no clear evidence for binarity is indicated in the spectra obtained to date.

Key words: stars: abundances – stars: fundamental parameters – stars: general

* Observations collected at the European Southern Observatory (ESO), La Silla, Chile.

Send offprint requests to: B. Barbuy

© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999

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