Spectral diagnostics of stellar coronae
Giulio Del Zanna (DAMTP, University of Cambridge UK)
Past and current satellites have provided a
wealth of XUV spectroscopic observations
of stellar coronae and transition regions (TR).
However, measurements of basic characteristics
have been elusive. For example, TR densities of
active stars have most probably been overestimated by
about an order of magnitude due to an incorrect assumption of
ionization equilibrium. Much of the results
(emission measures, temperatures, chemical abundances)
currently published also rely on the same assumption.
I review previous and new atomic data that allow direct
measurements of electron temperatures for 10 MK plasmas,
and use Chandra data to show that for some active
stars the electron temperatures are clearly at odds with
temperatures derived from emission measure distributions.
This indicates a possible breakdown of ionization equilibrium.
http://www.damtp.cam.ac.uk/user/astro/gd232/astro.html