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The Henize sample of S stars
I. The technetium dichotomy *
S. Van Eck and
A. Jorissen **
Received 20 November 1998 / Accepted 1 February 1999
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 and ) 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 Å have been obtained for 76 S stars, 8 M stars and 2 symbiotic stars.
The Å and 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 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
Send offprint requests to: S. Van Eck
Online publication: April 12, 1999