Observational Links Between Active Stellar Coronae and Solar Active Regions

Details Observational Links Between Active Stellar Coronae and Solar Active Regions Observational Links Between Active Stellar Coronae and Solar Active Regions

Apr 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999head....4.1801d&link_type=abstract

American Astronomical Society, HEAD meeting #4, #18.01; Bulletin of the American Astronomical Society, Vol. 31, p.721

Astronomy and Astrophysics

Astronomy

Scientific paper

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 <= log T <= 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~ 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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