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Published March 20, 2008 | Published
Journal Article Open

The Spitzer c2d survey of large, nearby, interstellar clouds. X. The Chamaeleon II pre-main-sequence population as observed with IRAC and MIPS


We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and NIR data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population in an area of similar to 1.75 deg^(2) and study the spatial distribution and properties of the cloud members and candidate pre-main-sequence (PMS) objects and their circumstellar matter. Our census is complete down to the substellar regime (M approximate to 0.03 M☉). From the analysis of the volume density of the PMS objects and candidates we find two groups of objects with volume densities higher than 25 M☉ pc^(-3) and 5-10 members each. A multiplicity fraction of about 13% +/- 3% is observed for objects with separations 0.8" < θ < 6.0" (142-1065 AU). No evidence for variability between the two epochs of the c2d IRAC data set, Δt ~ 6 hr, is detected. We estimate a star formation efficiency of 1%-4%, consistent with the estimates for Taurus and Lupus, but lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds reflect a different history of star formation. We also find that Cha II is turning some 6-7 M☉ into stars every Myr, which is low in comparison with the star formation rate in other c2d clouds. The disk fraction of 70%-80% that we estimate in Cha II is much higher than in other star-forming regions and indicates that the population in this cloud is dominated by objects with active accretion. Finally, the Cha II outflows are discussed; a new Herbig-Haro outflow, HH 939, driven by the classical T Tauri star Sz 50, has been discovered.

Additional Information

© 2008 American Astronomical Society. Received 2007 August 28; accepted 2007 November 17. We thank the anonymous referee for his careful reading and useful comments/suggestions. Support for this work, 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. This work was partially financed by the Istituto Nazionale di Astrofisica (INAF) through PRIN-INAF-2005. L. S. acknowledges financial support from PRIN-INAF-2005 (Stellar clusters: a benchmark for star formation and stellar evolution), and B. M. thanks the Fundación Ramón Areces for financial support. We thank T. Robitaille for discussions and help on the use of his accretion models and J. Kainulainen for providing an unpublished extinction map of Cha II and for discussions on extinction issues. We are also grateful to Ewine van Dishoeck for several discussions, comments, and suggestions on an earlier version of the paper and to Paul Harvey for the many discussions on the YSO selection and for his comments on the paper. We also thank Bo Reipurth for discussions on HH objects and B. Stelzer for communications on unpublished results of XMM-Newton observations in Cha II. We also thank Tyler Bourke for his comments. A special thanks to pussycat Matula for her assiduous and warm assistantship during the preparation of this manuscript. We acknowledge the c2d collaborators for the many discussions and suggestions during the telecons. This paper is based on observations carried out at the European Southern Observatory, La Silla and Paranal (Chile), under proposals 67.C-0225, 68.C-0311, 076.C-0385, and 078.C-0293. 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.

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