Observational clues for a role of circumstellar accretion in PMS X-ray activity

INAF - Osservatorio Astronomico di Palermo Giuseppe S. Vaiana, Palazzo dei Normanni, 90134 Palermo, Italy e-mail: giusi@oapa.astropa.unipa.it;sciorti@oapa.astropa.unipa.it

Corresponding author: E. Flaccomio, ettoref@oapa.astropa.unipa.it

Received: 25 June 2002
Accepted: 9 October 2002

Abstract

We revisit the published analyses of ROSAT X-ray observations of the star forming regions NGC 2264 and Chamaeleon I (∼3 and ∼5 Myr old respectively) in the light of newly published optical data. At odds with previous results on Chamaeleon I members, we find that low mass stars in both regions have near-saturated emission levels. Similarly to what previously found in the Orion Nebula Cluster, Weak Line T-Tauri Stars in NGC 2264 and in the Chamaeleon I cloud have higher X-ray activity levels respect to Classical T Tauri Stars, arguing in favor of a role of the disk and/or accretion in determining X-ray emission.