Light element non-LTE abundances of λ Bootis stars^*

II. Nitrogen and sulphur

¹ Leiden Observatory, Niels Bohrweg 2, PO Box 9513, 2300 RA Leiden, The Netherlands
² Institute of Astronomy, National Astronomical Observatory, and Isaac Newton Institute of Chile Bulgarian Branch, PO Box 136, 4700 Smolyan, Bulgaria e-mail: rozhen@mbox.digsys.bg
³ Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria e-mail: Ernst.Paunzen@univie.ac.at
⁴ Zentraler Informatikdienst der Universität Wien, Universitätsstr. 7, 1010 Wien, Austria
⁵ Departamento de Física, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, Argentina -Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, Argentina e-mail: opintado@tucbbs.com.ar
⁶ Visiting Astronomers at Complejo Astronomico El Leoncito
⁷ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF), Apartado de Correos 50727, 28080 Madrid, Spain e-mail: esm@vilspa.esa.es

Corresponding author: I. Kamp, kamp@strw.leidenuniv.nl

Received: 18 May 2001
Accepted: 31 May 2001

Abstract

One of the main characteristics proclaimed for the group of the λ Bootis stars is the apparent solar abundance of the light elements C, N, O and S. The typical abundance pattern is completed by the strong underabundances of the Fe-peak elements. In the first paper of this series, we have shown that carbon is less abundant than oxygen but both elements are still significantly more abundant than Fe-peak elements. The mean abundances, based on a detailed non-LTE investigation, were found -0.37 dex and -0.07 dex, respectively. As a further step, we now present non-LTE abundances of nitrogen and sulphur for thirteen members of the λ Bootis group based on several spectral lines between 8590 Å and 8750 Å. Furthermore, LTE abundances for calcium in the same spectral range were derived and compared with values from the literature. Similar to the mean abundances of carbon and oxygen, nearly solar values were found (-0.30 dex for nitrogen and -0.11 dex for sulphur) for our sample of program stars. Among our sample, one previously undetected binary system (HD 64491) was identified. From a statistical point of view, the abundances of the light elements range from slightly overabundant to moderately underabundant compared to the Sun. However, the individual objects always exhibit a similiar pattern, with the Fe-peak elements being significantly more underabundant than the light elements. No correlation of the derived abundances with astrophysical parameters such as the effective temperature, surface gravity or projected rotational velocity was found. Furthermore, the abundances of the light elements do not allow us to discriminate between any proposed theory.