A spectroscopic survey for λ Bootis stars^*

II. The observational data

¹ Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria
² Zentraler Informatikdienst der Universität Wien, Universitätsstr. 7, 1010 Wien, Austria
³ Department of Computer Science Keele University, Keele, Staffordshire, UK
⁴ Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada

Corresponding author: E. Paunzen, Ernst.Paunzen@univie.ac.at

Received: 3 April 2001
Accepted: 27 April 2001

Abstract

λ Bootis stars comprise only a small number of all A-type stars and are characterized as nonmagnetic, Population i, late B to early F-type dwarfs which show significant underabundances of metals whereas the light elements (C, N, O and S) are almost normal abundant compared to the Sun. In the second paper on a spectroscopic survey for λ Bootis stars, we present the spectral classifications of all program stars observed. These stars were selected on the basis of their Strömgren colors as λ Bootis candidates. In total, 708 objects in six open clusters, the Orion OB1 association and the Galactic field were classified. In addition, 9 serendipity non-candidates in the vicinity of our program stars as well as 15 Guide Star Catalogue stars were observed resulting in a total of 732 classified stars. The 15 objects from the Guide Star Catalogue are part of a program for the classification of apparent variable stars from the Fine Guidance Sensors of the Hubble Space Telescope. A grid of 105 MK standard as well as "pathological" stars guarantees a precise classification. A comparison of our spectral classification with the extensive work of Abt & Morrell ([CITE]) shows no significant differences. The derived types are 0.23 ± 0.09 (rms error per measurement) subclasses later and 0.30 ± 0.08 luminosity classes more luminous than those of Abt & Morrell ([CITE]) based on a sample of 160 objects in common. The estimated errors of the means are ± 0.1 subclasses. The characteristics of our sample are discussed in respect to the distribution on the sky, apparent visual magnitudes and Strömgren colors.