Astronomy & Astrophysics

Free access article

A&A 417, 651-665 (2004)
DOI: 10.1051/0004-6361:20030495

NEXXUS: A comprehensive ROSAT survey of coronal X-ray emission among nearby solar-like stars

J. H. M. M. Schmitt and C. Liefke

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
e-mail: cliefke@hs.uni-hamburg.de
(Received 19 February 2003 / Accepted 20 March 2003 )

Abstract
We present a final summary of all ROSAT X-ray observations of nearby stars. All available ROSAT observations with the ROSAT PSPC, HRI and WFC have been matched with the CNS4 catalog of nearby stars and the results gathered in the Nearby X-ray and XUV-emitting Stars data base, available via www from the Home Page of the Hamburger Sternwarte at the URL http://www.hs.uni-hamburg.de/DE/For/Gal/Xgroup/nexxus. New volume-limited samples of F/G-stars ( $d_{\rm lim} = 14$ pc), K-stars ( $d_{\rm lim} = 12$ pc), and M-stars ( $d_{\rm lim} = 6$ pc) are constructed within which detection rates of more than 90% are obtained; only one star (GJ 1002) remains undetected in a pointed follow-up observation. F/G-stars, K-stars and M-stars have indistinguishable surface X-ray flux distributions, and the lower envelope of the observed distribution at $F_{\rm X} \approx 10^4$ erg/cm ²/s is the X-ray flux level observed in solar coronal holes. Large amplitude variations in X-ray flux are uncommon for solar-like stars, but maybe more common for stars near the bottom of the main sequence; a large amplitude flare is reported for the M star LHS 288. Long term X-ray light curves are presented for $\alpha$ Cen A/B and Gl 86, showing variations on time scales of weeks and demonstrating that $\alpha$ Cen B is a flare star.

Key words: stars: activity -- stars: coronae -- stars: late-type -- X-rays: stars

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

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