S 10947 Aql = RX J2009.8+1557: A probable RS CVn star which sometimes stops its eclipses

Abstract

We report the discovery of a new variable star, called S 10947 Aql, as the likely optical counterpart of RX J2009.8+1557. The optical variability pattern as well as the detected X-ray emission suggest that it is a chromospherically active binary of the RS Canum Venaticorum type. We discovered an occasional disappearance of the eclipsing minima as well as large variations in the eclipse amplitude. We discuss possible causes of this peculiarity.

5 pages, LATEX with aa.sty, 4 ps-figs., A&A (accepted), also available at http://www.aip.de/~jcg/publis.html