Coronal properties of G-type stars in different evolutionary phases

¹ Dipartimento di Scienze Fisiche ed Astronomiche, Sezione di Astronomia, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy e-mail: scelsi@oapa.astropa.unipa.it
² INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

Received: 27 July 2004
Accepted: 6 November 2004

Abstract

We report on the analysis of XMM-Newton observations of three G-type stars in very different evolutionary phases: the weak-lined T Tauri star HD 283572, the Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com. They all have high X-ray luminosity (~10³¹ erg s^-1 for HD 283572 and 31 Com and ~10³⁰ erg s^-1 for EK Dra). We compare the Emission Measure Distributions (s) of these active coronal sources, derived from high-resolution XMM-Newton grating spectra, as well as the pattern of elemental abundances vs. First Ionzation Potential (FIP). We also perform time-resolved spectroscopy of a flare detected by XMM from EK Dra. We interpret the observed s as the result of the emission of ensembles of magnetically confined loop-like structures with different apex temperatures. Our analysis indicates that the coronae of HD 283572 and 31 Com are very similar in terms of dominant coronal magnetic structures, in spite of differences in the evolutionary phase, surface gravity and metallicity. In the case of EK Dra the distribution appears to be slightly flatter than in the previous two cases, although the peak temperature is similar.