Diagnozing star formation in the Chamaeleon–Musca dark cloud complex

Abstract

We present a comprehensive young stellar census of the Chamaeleon–Musca dark-cloud complex. Searching in a $12°\times 12°$ sky area using Gaia DR3 data for astrometric membership, aided by 2MASS and ALLWISE infrared colors for disk-bearing objects, we have found not only members known to be associated with main clouds, but also inter-cloud candidates discovered for the first time. We confirm that Cha I is active in starbirth with more than 200 members. Cha II harbors some 50 members, among which three are projected in northern Cha III, which itself lacks any star-forming activity. The subcluster Cha I South is at an average distance of $\sim$189 pc, slightly nearer than Cha I North at $\sim$192 pc, whereas Cha II is farther at $\sim$198 pc, forming a distance sequence. The isochrone fitting indicates a consistent age of about 3 Myr for Cha I and Cha II, suggesting coeval star formation. Our work confirms the Musca filament with the paucity of fully grown young stars. Serendipitously, in the foreground ($\sim$110 pc), some members of $ϵ$ Cha or LCC associations are projected in our studied field; they are more evolved pre-main sequence objects or dwarfs with an age spread of 5-20 Myr. Also detected in our data is a part of the cluster UPK 569 older ($\sim$30 My) and farther ($\sim$250 pc) than Chamaeleon clouds. An analysis of two separate clouds some 10 deg to the south-east, Cha-East I and Cha-East II, uncovers no young stars, lending support that Cha I and Cha II mark the end of the sequence of the latest episode of triggered star formation by the Sco-Cen OB association.