Heidelberg 2006 – scientific programme

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EP: Extraterrestrische Physik

EP 17: Sonne: Atmosph
äre

EP 17.3: Fachvortrag

Thursday, March 16, 2006, 09:45–10:00, B

Investigating stellar coronae using models of solar structures — •Pia Zacharias and Hardi Peter — Kiepenheuer-Institut für Sonnenphysik, 79104 Freiburg

In order to investigate the density and temperature structure of stellar coronae we describe them as being composed of a large number of coronal loops, i.e. as multi-loop coronae. Each of these loops is modeled by an analytical approximation to a static loop model or, even more simple, by well known scaling laws relating loop length, heating rate, temperature and pressure. We construct the stellar corona by assuming a distribution of loop lengths and heating rates, for which the loop densities and temperatures are calculated. From these the emission in various EUV and X-ray spectral lines is derived using the atomic data package CHIANTI. We now treat the spectrum integrated from all these loops as the spectrum from a hypothetic star, i.e. we analyze this spectrum with standard techniques used in stellar EUV and X-ray spectroscopy.

We find that the classical inversions of stellar spectra can give results for the average temperature or density of a star which are up to an order of magnitude off the peak of the respective distribution used as input for the multi-loop model. Nevertheless, the typical scale height of the corona derived from the synthesized spectrum matches the loop length quite well. This study shows the limitations of classical EUV and X-ray diagnostics to infer temperatures and densities from stellar spectra, but it also shows new ways how to derive such quantities in a more reliable way.