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We will report on our ROSAT Wide Field Camera (WFC) survey of all nondegenerate stars within 10 pc. Extreme ultraviolet (EUV) luminosity functions will be constructed for each stellar spectral type represented in this survey (F, G, K, and M) for comparison with each other and with X-ray luminosity functions previously derived from Einstein Imaging Proportional Counter (IPC) data. We will also study the effects of binarity and stellar rotation rate on EUV luminosity.
Since count rates from different EUV and X-ray spectral ranges can be used to determine possible coronal plasmas temperatures, the WFC count rates (for both the S1 and S2 filters) have been analyzed together with those of the Einstein IPC, the ROSAT Position Sensitive Proportional Counter, and the EXOSAT Low Energy Telescope with the 3000~\AA\ Lexan filter. We analyze in depth the advantages and limitations of using count rates from these different bandpasses together to constrain coronal temperatures. For a set of 18 stars in our survey, we have compared temperature solutions computed using multi-filter photometry with the IPC-derived temperature solutions of Schmitt et al.\ (1990 ApJ 365, 704). In general, the two temperature fits derived by the IPC are inconsistent with our results; our data imply that in many cases, the two temperatures derived by the IPC may be too low by about a factor of 2. While our analysis does suggest the existence of more than one temperature in the coronae of late-type stars, in many instances our data are inconsistent with the presence of a broad temperature distribution. This, together with the success of two temperature plasmas in fitting IPC data, implies that for many stars, the coronal emission measure distribution is in fact dominated by two distinct temperatures.
This work is supported by NASA grants NAGW-2904 and NAG5-1792 to the University of Colorado.
