An EXOSAT observation of 1.5 orbital cycles of the 0.7 day short-period RS CVn system ER Vul.
Abstract
Two Exosat observations of the short-period 0.7-day eclipsing RS Cvn binary system ER Vul are reported. The first observation in October 1984, lasted for 3 hr, while the second in May 1985, covered 1.5 orbital cycles. The overall counting rate decreased by a factor of about 2 in the 6 months separating the two observations. No strong orbital modulation of the X-ray flux was evident, nor were any deep eclipses seen. The spectrum measured in the 0.05-6 keV band was well fitted by a two-component thermal plasma model with temperaures of 6 and 40 million degrees. The failure to detect any strong orbital modulation indicates for both temperature components either loop heights larger than a stellar radius, or more compact loops that are uniformly distributed as a function of longitude. The failure to detect deep eclipses cannot convicingly be used to distinguish these two possibilities because only latitudes greater than 10 deg are occulted, although there was some evidence for a 10-20 percent occultation of the low-energy light curve at secondary optical eclipse.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 1987
- DOI:
- 10.1093/mnras/227.3.545
- Bibcode:
- 1987MNRAS.227..545W
- Keywords:
-
- Eclipsing Binary Stars;
- Exosat Satellite;
- Stellar Orbits;
- Light Curve;
- X Ray Astronomy;
- Astrophysics