Properties of X-ray flares on young stars

Thomas Preibisch & Ralph Neuhäuser

IAU Coll. 151: Flares and Flashes, eds. Greiner et al., Springer Verlag, p. 212


The interest in the giant flares found on young stars results from the fact that their energetics is vastly different from solar flares. The recent ROSAT observations of young clusters yield a good basis for a systematic study of these flares. We have investigated 18 very deep pointed observations of star forming regions in IC348, Chamaeleon, rho Ophiuchi, and Orion. To study the age dependence of the flare properties we also investigated observations of the young clusters IC2391, Pleiades, and Hyades. In this way we have evaluated the X-ray emission of several hundred young stars with ages ranging from about 10^6 years to 7 x 10^8 years. We have found 36 large flares on identified cluster members and have determined the flare properties with a simple flare model.

The flares show the same relation between the total X-ray flare energy and the quiescent X-ray luminosity as the dM star flares. The total X-ray flare energies decrease smoothly from the very high values found for very young stars to solar values with increasing cluster age. Our results indicate that the large flares on young stars are similar to scaled-up solar-like activity rather than to accretion processes.

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