A systematic analysis of X-ray variability of dM stars
A. Marino 1,
G. Micela 1 and
G. Peres 2
Received 24 November 1998 / Accepted 11 October 1999
We have systematically analyzed X-ray variability of dM stars. Our data base is the sample of all dM stars listed in the CNS3 (Gliese & Jahreiss 1991) catalog which have been observed with the ROSAT PSPC.
Our data sample includes 86 pointed observations of 55 distinct stars or multiple systems. A large fraction of stars shows significant variations, regardless of their quiescent flux. Variability is detected on all observable time scales. The amplitudes of these variations are independent of both stellar X-ray and visual luminosity. Compared to solar X-ray variability properties our results suggest that the amplitude distribution of X-ray variability in dM stars is consistent with the analogous distribution for solar flares.
We discuss the effect of variability on the spread observed in the X-ray luminosity function of M stars.
The comparison of our data with those obtained with Einstein IPC shows that variations on time scales shorter than a few month are more common than long term variations comparable to, e.g., the 11 years solar cycle.
Key words: stars: coronae stars: late-type X-rays: stars Galaxy: solar neighbourhood
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© European Southern Observatory (ESO) 2000
Online publication: December 8, 1999