HEAD Division Meeting 1999, April 1999
Session 18. Stellar Coronae
Poster, Tuesday, April 13, 1999, 8:30am-6:02pm, Gold Room

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[18.01] Observational Links Between Active Stellar Coronae and Solar Active Regions

Jeremy J. Drake (Smithsonian Astrophysical Observatory), Peres Giovanni (Universit\`a di Palermo), Salvatore Orlando (ESA Solar System Division, Space Science Dept., ESTEC), J. Martin Laming (Naval Research Laboratory), Antonio Maggio (Osservatorio Astronomico di Palermo)

Based on Yohkoh SXT observations of the Sun near peak activity level obtained on 6 January 1992, we search for coronal structures that have emission measure distributions EM(T) that match the observed stellar coronal emission measure distributions derived for the intermediate activity stars \epsilon~Eri (K2 V) and \xi~Boo~A (G8 V) from EUVE spectroscopic observations. We find that the temperatures of the peaks of the observed stellar distributions EM(T), as well as their slopes in the temperature range 6.0 \le \log T \le 6.5, are very similar to those obtained for the brightest of the solar active regions in the 6 January 1992 SXT images. The observed slopes correspond approximately to EM\propto T\beta with \beta~4, which is much steeper than predicted by static, uniformly heated loop models. Plasma densities in the coronae of \epsilon~Eri and \xi~Boo~A are also observed to be essentially the same as the plasma densities typical of solar active regions. These data provide the best observational support yet obtained for the hypothesis that solar-like stars up to the activity levels of \epsilon~Eri (K2 V) and \xi~Boo~A are dominated by active regions similar to those observed on the Sun. The surface filling factors of bright active regions needed to explain the observed stellar emission measures is approximately unity. Based on these results, we speculate on the nature of coronal structure at still higher levels of activity.

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