EXOSAT observations of the rapidly rotating flare star gliese 890

Abstract

We present the first X-ray observations of the late-type dwarf flare star Gliese 890 using the low-energy (LE) and the medium energy (ME) detectors of the EXOSAT Observatory. A steady X-ray emission, most probably of coronal origin, is detected. No flaring activity is observed in our X-ray observations. We have carried out a combined spectral fit to the LE and ME data and derived an X-ray plasma temperature of 1.4 ± 0.3 keV and the equivalent hydrogen column density of (7.5 ± 4.7) x 10¹⁹ cm^-2 using the plasma emission models given by Raymond and Smith. The X-ray luminosity in the 0.1-4.0 keV energy band is 4.1 × 10²⁹ ergs s^-1 . The X-ray luminosity and the temperature are typical of a slowly rotating dMe type flare star and do not show any effect of the fast rotation, possibly suggesting a saturation effect of the dynamo action. It appears unlikely that a hot white dwarf companion is hibernating in orbit around GI 890.