Spectroscopic properties of cool Ursa Major group members
  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. 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 A
and the Li abundance, and the infilling of the core of the H alpha line.
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. The studied stars infer an average Ursa Major
group iron abundance of -0.03+-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.
