A&A Supplement series, Vol. 126, December II 1997, 407-411
Received December 9, 1996; accepted April 3, 1997
E. Paunzen - R.O. Gray
Send offprint request: E. Paunzen
Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, A-1180 Wien, Austria
Department of Physics and Astronomy, Appalachian State University, Boone, North Carolina 28608, U.S.A.
In recent years, the chemically peculiar (CP) stars of the upper main sequence
have become a fruitful field for the testing of astrophysical theories.
such as diffusion, convection and mass loss have been developed theoretically
and introduced into models. The group of Bootis stars, however, is remarkable
among the chemically
peculiar stars as they are nonmagnetic, PopulationI, A to F-type dwarfs
which show significant underabundances of metals (except for C, N, O
and S). Unfortunately, the small number of confirmed members of the
Bootis class makes a sound statistical analysis of their properties impossible.
Thus, it is still difficult to decide between the two theories - mass loss
with diffusion and the accretion theory - which have
been proposed to explain the origin of these stars.
We therefore have started a spectroscopic survey to find new Bootis stars in the field as well as in open clusters and associations. The presence of Bootis stars in open clusters and associations would permit a determination of the ages of these stars, and thus would yield an important test for distinguishing between the two theories. In this paper we describe the selection of candidates using photometric criteria, the basic requirements, spectroscopic follow-up observations and results from the first three observing runs. Special care was taken to avoid misclassification of our programme stars (e.g. Bootis stars are often confused with intermediate PopulationII, He-weak or high stars), using a refined MK system. The discovery of at least six new Bootis stars (including three in the Orion OB1 association) shows the efficacy of our selection criteria.
keywords: surveys -- stars -- Bootis -- stars: chemically peculiar -- stars: early type; stars: fundamental parameters