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Astron. Astrophys. 345, 127-136 (1999)


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The Henize sample of S stars

I. The technetium dichotomy *

S. Van Eck and A. Jorissen **

Institut d'Astronomie et d'Astrophysique (IAA), Université Libre de Bruxelles, C.P.226, Boulevard du Triomphe, B-1050 Bruxelles, Belgium (svaneck; ajorisse@astro.ulb.ac.be)

Received 20 November 1998 / Accepted 1 February 1999

Abstract

This paper is the first one in a series investigating the properties of the S stars belonging to the Henize sample (205 S stars with [FORMULA] and [FORMULA]) in order to derive the respective properties (like galactic distribution and relative frequencies) of intrinsic (i.e. genuine asymptotic giant branch) S stars and extrinsic (i.e. post mass-transfer binary) S stars. High-resolution (R=30 000 to 60 000) spectra covering the range [FORMULA] Å have been obtained for 76 S stars, 8 M stars and 2 symbiotic stars.

The [FORMULA] Å and [FORMULA] Å blends involving a TcI line were analysed separately and yield consistent conclusions regarding the presence or absence of technetium. Only one `transition' case (Hen 140 = HD 120179, a star where only weak lines of technetium are detectable) is found in our sample. A resolution greater than R [FORMULA] is clearly required in order to derive unambiguous conclusions concerning the presence or absence of technetium. The Tc/no Tc dichotomy will be correlated with radial velocity and photometric data in a forthcoming paper.

Key words: stars: abundances – stars: binaries: symbiotic – stars: evolution – stars: AGB and post-AGB

* Based on observations carried out at the European Southern Observatory (ESO, La Silla, Chile)
** Research Associate, National Fund for Scientific Research (FNRS), Belgium

Send offprint requests to: S. Van Eck

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999

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