The active binary star II Pegasi with it BeppoSAX

Abstract

II Peg is an ideal target to study stellar activity and flares, since intense and long lasting flares have been frequently detected from this system at all wavelengths. We report here about a BeppoSAX observation of II Peg. We followed the system for ~ 19 hours on December 5 and 6 1997 with BeppoSAX and the X-ray light curve resembles the typical behavior of a decay phase of a long-lasting flare. The spectral analysis shows that the II Peg X-ray spectrum is described by a two-temperature components, with the two dominant temperatures centered in the range of 9-11 and 24-26 MK. The derived coronal metal abundance is low ( Z ~ 0.2 Z_sun) compared to recent determinations of the photospheric abundance (Z ~ 0.6 Z_sun). Some possible explanations for this phenomenology are reviewed. As for most other stellar coronal sources observed with BeppoSAX, we find that in order to fit the BeppoSAX spectra an interstellar column density about a factor ten higher than previously determined is required.