The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds.X. The Chamaeleon II Pre-Main Sequence Population as Observed With IRAC and MIPS

TL;DR

This study uses Spitzer IRAC and MIPS data to analyze the young stellar population in the Chamaeleon II cloud, revealing its star formation efficiency, multiplicity, and active accretion characteristics, along with discovering a new outflow.

Contribution

It provides the first comprehensive census of Cha II's pre-main sequence stars and their properties using combined infrared and optical data, highlighting differences from other clouds.

Findings

Identified two dense groups of young stars correlating with high extinction regions.

Estimated star formation efficiency of 1-4%, lower than in Cha I.

Found a high disk fraction of 70-80%, indicating active accretion.

Abstract

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.