Investigating the possible connection between λ Bootis stars and intermediate Population II type stars

¹ Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
e-mail: epaunzen@physics.muni.cz
² Rozhen National Astronomical Observatory, Institute of Astronomy of the Bulgarian Academy of Sciences, PO Box 136, 4700 Smolyan, Bulgaria
³ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ Institutionen för fysik och astronomi, Uppsala universitet, Box 516, 751 20 Uppsala, Sweden
⁵ Institute for Astrophysics, University of Vienna, Türkenschanzstr. 17, 1180 Vienna, Austria

Received: 16 March 2014
Accepted: 2 June 2014

Abstract

Context. The λ Bootis stars are located at the upper main sequence of the Hertzsprung-Russell diagram and exhibit a peculiar abundance pattern. The light elements (C, N, O, and S) present solar abundances whereas all other elements are moderately to strongly underabundant. It has not yet been determined whether that abundance pattern is intrinsic, or is restricted to the stellar surface.

Aims. If we follow the hypothesis that the λ Bootis stars are intrinsically metal-weak, then there should be a connection with the intermediate Population II and F-weak objects. Such a possible affinity has not been previously investigated.

Methods. We present detailed elemental abundances, including those of the light elements carbon and oxygen, for 38 bright intermediate Population II and F-weak objects. In addition, we investigate the kinematic characteristics of the groups.

Results. From photometric, spectroscopic, and kinematic data, there is no distinction between the intermediate Population II and F-weak type stars. We therefore conclude that the two groups are identical. However, it is possible to distinguish the λ Bootis stars from the intermediate Population II stars on the basis of elemental abundances, though not in terms of their kinematics.

Conclusions. The λ Bootis stars seem to be distinct from the intermediate Population II group. Further asteroseismologic investigations and analyses of spectroscopic binary systems are needed to strengthen this conclusion.