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Post Info TOPIC: Chamaeleon II (Cha II) dark cloud
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Chamaeleon dark clouds
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Title: Herschel's view of the large-scale structure in the Chamaeleon dark clouds
Author: C. Alves de Oliveira, N. Schneider, B. Merín, T. Prusti, A. Ribas, N. L. J. Cox, R. Vavrek, V. Könyves, D. Arzoumanian, E. Puga, G. L. Pilbratt, A. Kóspál, Ph. André, P. Didelon, A. Men'shchikov, R. Royer, C. Waelkens, S. Bontemps, E. Winston, L. Spezzi

The Chamaeleon molecular cloud complex is one of the nearest star-forming sites encompassing three molecular clouds with a different star-formation history, from quiescent (Cha III) to actively forming stars (Cha II), and reaching the end of star-formation (Cha I). To characterise its large-scale structure, we derived column density and temperature maps using PACS and SPIRE observations from the Herschel Gould Belt Survey, and applied several tools, such as filament tracing, power-spectra, \Delta-variance, and probability distribution functions of column density (PDFs), to derive physical properties. The column density maps reveal a different morphological appearance for the three clouds, with a ridge-like structure for Cha I, a clump-dominated regime for Cha II, and an intricate filamentary network for Cha III. The filament width is measured to be around 0.12\pm0.04 pc in the three clouds, and the filaments found to be gravitationally unstable in Cha I and II, but mostly subcritical in Cha III. Faint filaments (striations) are prominent in Cha I showing a preferred alignment with the large-scale magnetic field. The PDFs of all regions show a lognormal distribution at low column densities. For higher densities, the PDF of Cha I shows a turnover indicative of an extended higher density component, culminating with a power-law tail. Cha II shows a power-law tail with a slope characteristic of gravity. The PDF of Cha III can be best fit by a single lognormal. The turbulence properties of the three regions are found to be similar, pointing towards a scenario where the clouds are impacted by large-scale processes. The magnetic field could possibly play an important role for the star-formation efficiency in the Chamaeleon clouds if proven that it can effectively channel material on Cha I, and possibly Cha II, but probably less efficiently on the quiescent Cha III cloud.

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RE: Chamaeleon II (Cha II) dark cloud
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Title: Chamaeleon
Authors: Kevin L. Luhman

The dark clouds in the constellation of Chamaeleon have distances of 160-180 pc from the Sun and a total mass of ~5000 M_sun. The three main clouds, Cha I, II, and III, have angular sizes of a few square degrees and maximum extinctions of A_V=5-10. Most of the star formation in these clouds is occurring in Cha I, with the remainder in Cha II. The current census of Cha I contains 237 known members, 33 of which have spectral types indicative of brown dwarfs (>M6). Approximately 50 members of Cha II have been identified, including a few brown dwarfs. When interpreted with the evolutionary models of Chabrier and Baraffe, the H-R diagram for Cha I exhibits a median age of ~2 Myr, making it coeval with IC 348 and slightly older than Taurus (~1 Myr). The IMF of Cha I reaches a maximum at a mass of 0.1-0.15 M_sun, and thus closely resembles the IMFs in IC 348 and the Orion Nebula Cluster. The disk fraction in Cha I is roughly constant at ~50% from 0.01 to 0.3 M_sun and increases to ~65% at higher masses. In comparison, IC 348 has a similar disk fraction at low masses but a much lower disk fraction at M>1 M_sun, indicating that solar-type stars have longer disk lifetimes in Cha I.

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Title: The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds.X. The Chamaeleon II Pre-Main Sequence Population as Observed With IRAC and MIPS
Authors: Juan M.Alcala', Loredana Spezzi, Nicholas Chapman, Neal J. Evans II, Tracy L. Huard, Jes K. Jorgens, Bruno Merin, Karl R. Stapelfel, Elvira Covino, Antonio Frasca, Davide Gandolfi, Isa Oliveira

We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and near infrared data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population of Cha II, in a mapped area of ~1.75 square degrees, and study the spatial distribution and properties of the cloud members and candidate pre-main sequence (PMS) objects and their circumstellar matter. From the analysis of the volume density of the PMS objects and candidates we find two tight groups of objects with volume densities higher than 25 solar masses per cubic parsec and 5-10 members each. These groups correlate well in space with the regions of high extinction. A multiplicity fraction of about 13% is observed for objects with separations between 0.8" and 6.0". Using the results of masses and ages from a companion paper, we estimate the star formation efficiency to be 1-4% significantly 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 the Cha II cloud is turning some 6-7 solar masses into stars every Myr, which is low in comparison with the star formation rate in other c2d clouds. On the other hand, 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, with particular regard to the discovery of a new Herbig-Haro outflow, HH 939, driven by the classical T Tauri star Sz 50.

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