Crazy Coronal Abundances

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Sep 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001tysc.confe..20l&link_type=abstract

Two Years of Science with Chandra, Abstracts from the Symposium held in Washington, DC, 5-7 September, 2001, meeting abstract.

Computer Science

Normal Stars And White Dwarfs

Scientific paper

Chandra high resolution spectra of active late-type stars show a pattern of strange coronal abundances. Elements with low first ionization potential (FIP < 10 eV) like Fe are underabundant, whereas elements with FIP > 10 eV (in particular, Ne and Ar) are overabundant compared to solar photospheric values. Preliminary evidence for this pattern was already seen in the ROSAT and ASCA data, but the Chandra and XMM-Newton data greatly strengthen the case. The coronal abundances in active stars are especially interesting because the solar corona shows the opposite effect (FIP deficiency). We will summarize the new results and comment on their limitations. In particular, We will present the coronal abundances of four active stars observed with the HETG - AB Dor, AU Mic, 44 Boo, and σ2 CrB. The solar FIP and stellar anti-FIP effects can be understood (at least in part) in terms of fractionation effects in the chromosphere and perhaps diffusion in the corona. We will present theoretical and heuristic models that can explain the observed crazy coronal abundances.

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