Open AccessAbundances of metal‐weak thick‐disc candidates
Author(s) -
Bonifacio P.,
Centurion M.,
Molaro P.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02866.x
Subject(s) - physics , stars , astrophysics , halo , metallicity , metal , galactic halo , abundance (ecology) , thick disk , spectral line , proper motion , astronomy , galaxy , chemistry , organic chemistry , fishery , biology
High‐resolution spectra of five candidate metal‐weak thick‐disc stars suggested by Beers & Sommer‐Larsen are analysed to determine their chemical abundances. The low abundance of all the objects has been confirmed, with metallicity reaching [Fe/H]=−2.9. However, for three objects the astrometric data from the Hipparcos catalogue suggest they are true halo members. The remaining two, for which proper‐motion data are not available, may have disc‐like kinematics. It is therefore clear that it is useful to address properties of putative metal‐weak thick‐disc stars only if they possess full kinematic data. For CS 22894−19 an abundance pattern similar to those of typical halo stars is found, suggesting that chemical composition is not a useful discriminant between thick‐disc and halo stars. CS 29529−12 is found to be C‐enhanced with [C/Fe]=+1.0; other chemical peculiarities involve the s‐process elements: [Sr/Fe]=−0.65 and [Ba/Fe]=+0.62, leading to a high [Ba/Sr], considerably larger than that found in more metal‐rich carbon‐rich stars, but similar to those in LP 706‐7 and LP 625‐44, discussed by Norris et al. Hipparcos data have been used to calculate the space velocities of 25 candidate metal‐weak thick‐disc stars, thus allowing us to identify three bona fide members, which support the existence of a metal‐poor tail of the thick disc, at variance with a claim to the contrary by Ryan & Lambert.