Astron. Astrophys. 364, L6-L12 (2000)

Letter to the Editor

Abundance analysis of two extremely metal-poor stars from the Hamburg/ESO Survey ^*

E. Depagne ¹, V. Hill ², N. Christlieb ³ and F. Primas <sup>2

1</sup> Observatoire de Paris-Meudon, 92125 Meudon Cedex, France (Eric.Depagne@obspm.fr)
² European Southern Observatory, 85748 Garching, Germany ([vhill,fprimas]@eso.org)
³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany (nchristlieb@hs.uni-hamburg.de)

Received 10 August 2000 / Accepted 25 August 2000

Abstract

We report on the first high spectral resolution analysis of extremely metal-poor halo stars from the Hamburg/ESO objective-prism survey (HES). The spectra were obtained with UVES at VLT-UT2. The two stars under investigation (HE 1303-2708 and HE 1353-2735) are main-sequence turnoff-stars having metal abundances of and -3.20, respectively. The stellar parameters derived from the UVES spectra are in very good agreement with those derived from moderate-resolution follow-up spectra. HE 1353-2735 is a double-lined spectroscopic binary.

The two stars nicely reproduce the strong scatter in [Sr/Fe] observed for extremely metal-poor stars. While we see a strong Sr II Å line in the spectrum of HE 1303-2708 (), we can only give an upper limit for HE 1353-2735 (), since the line is not detected. We report abundances of Mg, Ca, Sc, Ti, Cr for both stars, and Co, Y for HE 1303-2708 only. These abundances do not show any abnormalities with respect to known trends for metal-poor stars. Lithium is also detected in these stars, to a level which places them among Lithium-plateau metal-poor dwarfs.

Key words: stars: abundances stars: binaries: spectroscopic stars: fundamental parameters stars: individual: stars: subdwarfs surveys

* Based on observations collected at the European Southern Observatory, Paranal, Chile

Send offprint requests to: Eric.Depagne@obspm.fr

SIMBAD Objects

Contents

• 1. Introduction
• 2. HES candidate selection and spectroscopic follow-up
• 3. UVES observations
• 4. Stellar parameters and abundances
  • 4.1. Parameter determination methods
  • 4.2. Specific methods for HE 1353-2735
  • 4.3. Abundance determination
• 5. Discussion
  • 5.1. Stellar parameters
  • 5.2. -elements
  • 5.3. s-process elements
  • 5.4. Lithium
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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