Abstract
Context. Chamaeleon is the southernmost low-mass star-forming complex within 200 pc from the Sun. Its stellar population has been extensively studied in the past, but the current census of the stellar content is not complete yet and deserves further investigation. Aims. We take advantage of the second data release of the Gaia space mission to expand the census of stars in Chamaeleon and to revisit the properties of the stellar populations associated to the Chamaeleon I (Cha I) and Chamaeleon II (Cha II) dark clouds. Methods. We perform a membership analysis of the sources in the Gaia catalogue over a field of 100 deg2 encompassing the Chamaeleon clouds, and use this new census of cluster members to investigate the 6D structure of the complex. Results. We identify 188 and 41 high-probability members of the stellar populations in Cha I and Cha II, respectively, including 19 and 7 new members. Our sample covers the magnitude range from G = 6 to G = 20 mag in Cha I, and from G = 12 to G = 18 mag in Cha II. We confirm that the northern and southern subgroups of Cha I are located at different distances (191.4−0.8+0.8 pc and 186.7−1.0+1.0 pc), but they exhibit the same space motion within the reported uncertainties. Cha II is located at a distance of 197.5−0.9+1.0 pc and exhibits a space motion that is consistent with Cha I within the admittedly large uncertainties on the spatial velocities of the stars that come from radial velocity data. The median age of the stars derived from the Hertzsprung-Russell diagram and stellar models is about 1−2 Myr, suggesting that they are somewhat younger than previously thought. We do not detect significant age differences between the Chamaeleon subgroups, but we show that Cha II exhibits a higher fraction of disc-bearing stars compared to Cha I. Conclusions. This study provides the most complete sample of cluster members associated to the Chamaeleon clouds that can be produced with Gaia data alone. We use this new census of stars to revisit the 6D structure of this region with unprecedented precision.
Highlights
The molecular cloud complex in the southern constellation of Chamaeleon hosts one of the richest populations of T Tauri stars in the Solar neighbourhood
We compute the true positive rate (TPR, i.e. the fraction of synthetic cluster members recovered by our methodology) and contamination rate (CR, i.e. the fraction of synthetic field stars identified by our model as cluster members) of the classifier to better evaluate our results obtained with different pin values
We confirm most of the historical members from the literature and increase the samples of cluster members by 11% and 21% in Chamaeleon I (Cha I) and Chamaeleon II (Cha II), respectively
Summary
The molecular cloud complex in the southern constellation of Chamaeleon hosts one of the richest populations of T Tauri stars in the Solar neighbourhood. Roccatagliata et al (2018) used the parallaxes from the second data release of the Gaia space mission (Gaia-DR2, Gaia Collaboration 2018) to revisit the distance to Cha I These latter authors reported distances of 192.7+−00..44 pc and 186.5+−00..77 pc to the northern and southern subgroups of stars in this cloud, respectively. The scarcity of trigonometric parallaxes and radial velocity (RV) information for most stars in Chamaeleon has been the main limitation to studying the kinematic properties of this region This situation has dramatically changed with the advent of the GaiaDR2 catalogue combined with the spectroscopic observations conducted by the Gaia-ESO Survey (Gilmore et al 2012) in the Chamaeleon region (see e.g., Sacco et al 2017).
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