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Published June 20, 2008 | Published
Journal Article Open

The young population of the Chamaeleon II dark cloud


We discuss the results of the optical spectroscopic follow-up of pre-main-sequence (PMS) objects and candidates selected in the Chamaeleon II dark cloud based on data from the Spitzer Legacy survey "From Molecular Cores to Planet Forming Disks" (c2d) and from previous surveys. Our sample includes both objects with infrared excess selected according to c2d criteria and referred to as young stellar objects and other cloud members and candidates selected from complementary optical and near-infrared data. We characterize the sample of objects by deriving their physical parameters. The vast majority of objects have masses M ≤ 1 M_☉ and ages <6 Myr. Several of the PMS objects and candidates lie very close to or below the hydrogen-burning limit. A first estimate of the slope of the initial mass function in Cha II is consistent with that of other T associations. The star formation efficiency in the cloud (1%-4%) is consistent with our own estimates for Taurus and Lupus, but significantly lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds may reflect a different history of star formation. We also find that the Cha II cloud is turning some 8 M_☉ into stars every megayear, which is less than the star formation rate in the other c2d clouds. However, the star formation rate is not steady and evidence is found that the star formation in Cha II might have occurred very rapidly. The Hα emission of the Cha II PMS objects, as well as possible correlations between their stellar and disk properties, is also investigated.

Additional Information

© 2008 The American Astronomical Society. Received 2007 December 11, accepted for publication 2008 February 27. We are grateful to an anonymous referee for his/her very constructive comments and suggestions. This paper is based on observations carried out at the European Southern Observatory, Paranal (Chile), under observing programs 076.C-0385 and 078.C-0293. This work was partially financed by the Istituto Nazionale di Astrofisica (INAF) through PRIN-INAF-2005. Support for thiswork, part of the Spitzer Legacy Science Program, was provided by NASA through contract 1224608 issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. L. S. acknowledges financial support from PRIN-INAF-2005 (Stellar Clusters: A Benchmark for Star Formation and Stellar Evolution). We are grateful to Dan Jaffefor his careful reading and for his valuable comments/suggestions to the paper.We thank the c2d collaborators for the many discussions and suggestions during the telecons. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the National Science Foundation. We also acknowledge extensive use of the SIMBAD database. We are also grateful to many others, in particular to Salvatore Spezzi.

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