Ness, Jan-Uwe

Contact Email: jness@hs.uni-hamburg.de
Institute: University Hamburg, Gojenbergsweg 112, D-21029
Hamburg, Germany
First Coauthor: Rolf Mewe
Institute: Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
Second Coauthor: Anton J.J. Rassen
Institute: Space Research Organization Netherlands (SRON), Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
Research URL:http://www.hs.uni-hamburg.de/german/persons/ness_e.html
Presenting Thesis: Yes
Subject Area: Single Stars
Waveband: X-rays
Technique: Spectroscopy
Presentation: Oral Contribution: Thursday
Title: Influence of radiation fields on the density diagnostics of coronae of late-type stars: Algol and Procyon
Abstract: Spectroscopic density diagnostics based on He-like triplets have been common to investigate the structure of the solar corona for more than three decades. With the new instrumentation onboard Chandra and XMM this method of analysis can now also be applied to stellar coronae. In collision-dominated plasmas the ratio R=f/i of the forbidden line ( $1s2s\> 3S_1 \to 1s^2 1S_0$), disappearing in high density plasmas, and the intercombination line ( $1s2p\>3P_{2,1} -> 1s^2 1S_0$), increasing in higher density plasmas on cost of the forbidden line, is used as a sensitive indicator of electron density, yielding high values of R for low densities ( $n_e < 10^9 {\rm cm}^{-3}$). Measuring a low flux in the forbidden line compared to theintercombination line, however, is not always an indicator for high densities, it might also indicate that the depopulation of the forbidden line level ( $1s2\>3S_1 \to 1s2p\> 3P_{2,1}$) is due to a relatively strong UV radiation field instead of due to collisions in a high-density plasma. We illustrate this effect with Chandra LETGS measurements of the binary Algol, consisting of an X-ray dark B star and a K-star with a very active corona, and the inactive F star Procyon. Focussing on the triplets of CV, NVI, OVII, and NeIX, we show that the radiation fields might have significant influence on the density analysis of the low-Z ions of C, N and O in both cases, despite of the different radiation dilution factors. The sources of the UV radiation are of completely different origin for the two stars. While for Procyon the radiation originates from the stellar surface, the radiation in the case of Algol is supplied by the companion B star. A detailed investigation of whether the observed part of Algol's corona is actually illuminated by the radiation field of the B star, is necessary.