Carbon and nitrogen abundances in the coronae of Algol B and other evolved stars: Evidence for CNO-cycle processed material

Free access article

Issue		A&A Volume 388, Number 1, June II 2002


Page(s)		L13 - L16
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20020558

A&A 388, L13-L16 (2002)
DOI: 10.1051/0004-6361:20020558

Letter

Carbon and nitrogen abundances in the coronae of Algol B and other evolved stars: Evidence for CNO-cycle processed material

J. H. M. M. Schmitt and J.-U. Ness

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

(Received 21 March 2002 / Accepted 10 April 2002 )

Abstract
Using the Ly $_{\alpha}$ -lines of carbon and nitrogen measured in Chandra Low Energy Transmission Grating Spectrometer (LETGS) spectra we study the coronal abundances of these elements in a sample of late-type stars including dwarf stars, the prototypical eclipsing binary Algol, the single giant $\beta$ Cet, and three RS CVn binaries. In the main sequence stars of our sample the flux ratio $R_{\rm NC}$ between the Ly $_{\alpha}$ -lines of nitrogen and carbon is below unity, while $R_{\rm NC}$ is found to be $\approx$ 8.5 for $\beta$ Cet and >23.3 for Algol. These values are more than an order of magnitude larger than expected from a solar abundance plasma in collisional equilibrium regardless of the chosen temperature structure. We therefore interpret the anomalously large $R_{\rm NC}$ -ratios as being due to the exposure of processed material at the surfaces and in the coronae of Algol and $\beta$ Cet.

Key words: stars: abundances -- stars: activity -- stars: coronae -- stars: late type X-rays: stars -- stars: individual: Algol

Offprint request: J. H. M. M. Schmitt, jschmitt@hs.uni-hamburg.de

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