A study of coronal abundances in RS CVn binaries ^*

¹ Paul Scherrer Institut, Würenlingen & Villigen, 5232 Villigen PSI, Switzerland
² Institute of Astronomy, ETH Zentrum, 8092 Zürich, Switzerland
³ Space Research Organization of the Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Corresponding author: M. Audard, audard@astro.columbia.edu

Received: 18 September 2002
Accepted: 21 November 2002

Abstract

We present XMM-Newton data of several RS CVn binary systems. High-resolution X-ray spectra obtained with the Reflection Grating Spectrometers have been interpreted simultaneously with the European Photon Imaging Camera spectra. Highly active stars show a depletion of elements with a low first ionization potential (FIP) relative to high-FIP elements, whereas intermediately active binaries show either no FIP bias or a possible solar-like FIP effect. We find that the low-FIP abundance ratios to oxygen vary with the coronal average temperature whereas the ratios for high-FIP elements stay constant. Since we observe that the absolute Fe (low-FIP) abundance increases with decreasing activity, this suggests that the abundances of elements with low FIP vary with the coronal activity level. Compared with laboratory measurements of the intensity ratios of the 15.01 and 15.26 Å  lines, the coronal plasmas are in the optically thin regime.