Volume 505, Number 1, October I 2009
|Page(s)||299 - 306|
|Published online||24 July 2009|
No first ionization potential fractionation in the active stars AR Piscium and AY Ceti*
Laboratorio de Astrofísica Estelar y Exoplanetas, Centro de Astrobiología / CSIC-INTA, LAEFF Campus, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: email@example.com
2 INAF – Osservatorio Astronomico di Palermo G. S. Vaiana, Piazza del Parlamento, 1, 90134 Palermo, Italy e-mail: [affer;giusi]@astropa.inaf.it
Accepted: 1 July 2009
Context. The comparison of coronal and photospheric abundances in cool stars is an essential question to resolve. In the Sun an enhancement of the elements with low first ionization potential (FIP) is observed in the corona with respect to the photosphere. Stars with high levels of activity seem to show a depletion of elements with low FIP when compared to solar standard values; however, the few cases of active stars in which photospheric values are available for comparison lead to confusing results, and an enlargement of the sample is mandatory for solving this longstanding problem.
Aims. We calculate in this paper the photospheric and coronal abundances of two well known active binary systems, AR Psc and AY Cet, to get further insight into the complications of coronal abundances.
Methods. Coronal abundances of 9 elements were calculated by means of the reconstruction of a detailed emission measure distribution, using a line-based method that considers the lines from different elements separately. Photospheric abundances of 8 elements were calculated using high-resolution optical spectra of the stars.
Results. The results once again show a lack of any FIP-related effect in the coronal abundances of the stars. The presence of metal abundance depletion (MAD) or inverse FIP effects in some stars could stem from a mistaken comparison to solar photospheric values or from a deficient calculation of photospheric abundances in fast-rotating stars.
Conclusions. The lack of FIP fractionation seems to confirm that Alfvén waves combined with pondermotive forces are dominant in the corona of active stars.
Key words: stars: coronae / stars: abundances / stars: individual: AR Psc / X-rays: stars / line: identification / stars: individual: AY Cet
© ESO, 2009
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