Coronal abundances of X-ray bright pre-main sequence stars in the Taurus molecular cloud

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
³ Paul Scherrer Institut, Würenlingen and Villigen, 5232 Villigen PSI, Switzerland

Received: 4 May 2007
Accepted: 5 July 2007

Abstract

Aims.We studied the thermal properties and chemical composition of the X-ray emitting plasma of a sample of bright members of the Taurus Molecular Cloud to investigate possible differences among classical and weak-lined T Tauri stars, and possible dependences of the abundances on the stellar activity level and/or on the presence of accretion/circumstellar material.

Methods.We used medium-resolution X-ray spectra obtained with the sensitive EPIC/PN camera in order to analyze the possible sample. The PN spectra of 20 bright (L_X ~ 10³⁰–10³¹ erg s^-1) Taurus members, with at least ~ 4500 counts, were fitted using thermal models of optically thin plasma with two components and variable abundances of O, Ne, Mg, Si, S, Ar, Ca, and Fe. Extensive preliminary investigations were employed to study the performances of the PN detectors regarding abundance determinations, and finally to check the results of the fittings.

Results.We found that the observed X-ray emission of the studied stars can be attributed to coronal plasma having similar thermal properties and chemical composition both in the classical and in the weak-lined T Tauri stars. The results of the fittings did not reveal a correlation between the abundance patterns and activity or accretion/disk presence. The iron abundance of these active stars is significantly lower than the solar photospheric value (~ 0.2 solar). An indication of slightly different coronal properties in stars with different spectral type is found in this study. G-type and early K-type stars have, on average, slightly higher Fe abundances (Fe ~ 0.24 solar) than stars with later spectral type (Fe ~ 0.15 solar), confirming previous findings from high-resolution X-ray spectroscopy. Stars of the former group are also found to have, on average, hotter coronae.