EDP Sciences
Free access
Volume 508, Number 2, December III 2009
Page(s) 677 - 693
Section Galactic structure, stellar clusters, and populations
DOI http://dx.doi.org/10.1051/0004-6361/200912660
Published online 21 October 2009
A&A 508, 677-693 (2009)
DOI: 10.1051/0004-6361/200912660

Spectroscopic properties of cool Ursa Major group members

M. Ammler-von Eiff1, 2, 3, 4 and E. W. Guenther5

1  Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
2  Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
3  Astophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergäßchen 2-3, 07745 Jena, Germany
4  Georg-August-Universität Göttingen, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
    e-mail: mammler@uni-goettingen.de
5  Thüringer Landessterwarte Tautenburg, 07778 Tautenburg, Germany

Received 18 June 2009 / Accepted 2 September 2009

Context. Until now, most members of the Ursa Major (UMa) group of stars have been identified by means of kinematic criteria. However, in many cases kinematic criteria alone are insufficient to ascertain, whether an individual star is really a member of this group. Since photometric criteria are ineffective in the case of cool dwarf members, one must use spectroscopic criteria. Nevertheless, resulting membership criteria are inconclusive.
Aims. We reanalyse spectroscopic properties of cool UMa group dwarfs. In particular, we study the distribution of iron abundance, the strength of the Li I absorption at 6708 Å and the Li abundance, and the infilling of the core of the H$\alpha$ line.
Methods. Twenty-five cool and northern bona-fide members are carefully selected from the literature. Homogeneously measured stellar parameters and iron abundances are given for all Sun-like stars selected, based on spectra of high resolution and high signal-to-noise ratio. In addition, we measure the Li equivalent width and abundance as well as the relative intensity of the H$\alpha$ core and the corresponding chromospheric flux.
Results. The studied stars infer an average Ursa Major group iron abundance of -0.03$\pm$0.05 dex, which is higher by about 0.06 dex than determined elsewhere. The Li abundance derived of Ursa Major group dwarf stars is higher than in the Hyades at effective temperatures cooler than the Sun, but lower than in the younger Pleiades, a result which is independent of the exact value of the effective temperature adopted. The Sun-like and cooler dwarfs also display chromospheric infilling of the H$\alpha$ core. We present spectroscopic criteria that may be used to exclude non-members.

Key words: stars: abundances -- stars: fundamental parameters -- open clusters and associations: individual: Ursa Major group -- solar neighborhood

© ESO 2009