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FLARE HEATING IN STELLAR CORONAE Vinay L. Kashyap and Jeremy J. Drake

Vinay L. Kashyap and Jeremy J. Drake
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138;
vkashyap@cfa.harvard.edu, jdrake@cfa.harvard.edu
Manuel Gu¨del and Marc Audard
Laboratory for Astrophysics, Paul Scherrer Institute, Wu¨renlingen and Villigen, 5232 Villigen PSI, Switzerland;
guedel@astro.phys.ethz.ch, audard@astro.phys.ethz.ch
Received 2002 March 25; accepted 2002 August 2
An open question in the field of solar and stellar astrophysics is the source of heating that causes stellar
coronae to reach temperatures of millions of degrees. One possibility is that the coronae are heated by a large
number of small flares. On the Sun, flares with energies as low as those of microflares are distributed with
energy as a power law of the form dN=dEđ Ţ / EŔ, with % 1:8, and appears to increase to values of 2.2­
2.7 for flares of lower energy. If the slope exceeds the critical value of 2, then in principle the entire coronal
energy input can be ascribed to flares that are increasingly less energetic but are more numerous. Previous
analyses of flares in light curves of active stars have shown that this index generally is greater than 2, although
it may be as low as 1.6 when strong flares alone are considered. Here we investigate the contribution of very
weak flares, covering the milliflare energy range, to the coronal luminosity of low-mass active stars. We ana-
lyze Extreme Ultraviolet Explorer/Deep Survey events data from FK Aqr, V1054 Oph, and AD Leo and con-


Source: Audard, Marc - INTEGRAL Science Data Centre & Observatory of Geneva, Université de Genčve


Collections: Physics