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Stellar Coronae

Published online by Cambridge University Press:  30 March 2016

G. S. Vaiana
G. S. Vaiana*
Affiliation:
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA and Osservatorio Astronomico, Palermo

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The standard theory of stellar coronae requires the presence of vigorous surface convection. In consequence, the expectation of such a theory is that stellar x-ray emission — if due to a corona — should be limited to a subset of stars (principally those of main sequence spectral types F and G), and therefore should be relatively rare. This theory also makes detailed predictions about coronal heating, which are subject to test if spatially resolved coronal data are available. We are now in a position to subject the standard coronal scenarios to observational scrutiny on both counts: Skylab and later observations have supplied us with spatially resolved data of the solar corona, while the succession of high-energy x-ray astronomy satellites, culminating with EINSTEIN, now gives us a long-awaited glimpse of stellar x-ray emission throughout the K-R diagram.

I will maintain that these new data imply that coronal x-ray emission dominantly derives from plasma structure confined by stellar surface magnetic fields; that coronal heating is likely to be non-acoustic in character and involves the confining magnetic fields; that stellar x-ray emission is not well correlated with the level of surface convection activity. These results of course cast serious doubt upon the viability of the standard theory of stellar coronal formation. In the following, I will try to very briefly summarize the solar and stellar data, to present the context in which they were initially obtained, and very briefly sketch the new coronal picture we are pursuing. The results presented here are excerpted from lectures presented by R. Rosner and myself recently at Erice, Italy (viz. Vaiana 1979) and from the preliminary results of the EINSTEIN Stellar Survey (Vaiana et al. 1979). The latter, part of a larger effort in x-ray astronomy led by R. Giacconi, involves the work of many people, including F.R. Harnden, L. Golub, P. Gorenstein, R. Rosner, F. Seward, K. Topika at CFA, as well as a number of EINSTEIN guest investigators.

Type
Joint Discussion
Information
Highlights of Astronomy , Volume 5: Highlights of Astronomy. As presented at the XVIIth General Assembly of the IAU, 1979 , 1980 , pp. 419 - 428
Copyright
Copyright © Cambridge University Press 1980

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