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Astron. Astrophys. 355, 629-638 (2000)

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A ROSAT pointed observation of the Chamaeleon II dark cloud *

J.M. Alcalá 1,6, E. Covino 1, M.F. Sterzik 2, J.H.M.M. Schmitt 3, J. Krautter 4 and R. Neuhäuser 5

1 Osservatorio Astronomico di Capodimonte, 80131 Napoli, Italy
2 European Southern Observatory, Casilla 19001, Santiago 19, Chile
3 Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
4 Landessternwarte Königstuhl, 69117 Heidelberg, Germany
5 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching, Germany
6 Instituto Nacional de Astrofísica, Optica y Electrónica, A.P. 51 y 216 C.P. 72000, Puebla, México

Received 23 September 1999 / Accepted 13 January 2000


A deep 13.5 ksec ROSAT PSPC pointed observation in the Chamaeleon II (Cha II) cloud is reported. 40 X-ray sources are detected of which 14 can be identified with previously known young stellar objects (YSOs), namely IRAS sources, classical T Tauri stars and weak T Tauri stars. From spectroscopic follow-up observations, four new weak T Tauri candidates have been found. The X-ray sources are mainly located on the north-east of the cloud and their spatial distribution follows the lanes of the 100µm dust emission. Their X-ray properties are similar to those of low-mass PMS stars. None of the protostar candidates in Cha II has been detected in the ROSAT pointed observation, in agreement with the ASCA observations results. The X-ray detection rates indicate that the weak T Tauri stars (WTTS) are less numerous than the classical T Tauri stars (CTTS), contrarily to the findings in Chamaeleon I (Cha I) and other star forming regions where the WTTS may outnumber the CTTS. The latter result could be a consequence of the fact that Cha II is in an earlier evolutionary stage as compared to Cha I, as conjectured by previous studies. The Cha II young stellar objects (YSOs) are, on the average, slightly less X-ray luminous than those in Cha I, but the normalised X-ray luminosity distribution functions of the two regions are not significantly different.

Key words: surveys – stars: formation – stars: low-mass – stars: pre-main sequence – ISM: individual objects: Chamaeleon clouds – X-rays: stars

* Based on observations with the European Southern Observatory, La Silla, Chile under proposal number 55.E-0792

Send offprint requests to: J.M. Alcalá

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000