ROSAT CORONAL TEMPERATURES OF YOUNG LATE-TYPE STARS

We analyze ROSAT X-ray spectra of a sample of young late type stars by fitting them with a continuous emission measure model with power-law temperature dependence up to a maximum temperature. This model gives s uccessful fits to all spectra of our sample. While most of the spectra can also fitted equally successful with the frequently used two tempe rature model, we argue and provide evidence that the continuous temper ature distribution model probably describes the coronal temperature st ructure in a more meaningful way. From our fitting results we find a v ery good correlation between the X-ray surface flux and the maximum co ronal temperature with the functional form F-X proportional to T-max(( 2.2+/-0.2)). This correlation extends over several orders of magnitude and is valid for the very young T Tauri stars as well as for the much older young main sequence stars in our sample. Since the X-ray surfac e flux is a good measure of the stellar activity and shows a clear dep endence on the stellar rotational velocity, the correlation means that the coronal temperature is related to the X-ray activity and ultimate ly determined by stellar rotation. Finally, we interpret our results w ith a simple analytic loop model and find that the coronae of the acti ve young stars are probably dominated by loops with generally higher p ressure as compared to typical solar active region loops.