New low-mass members of Chamaeleon I and ϵ Cha

Abstract

Aims: The goal of this paper is to increase the membership list of the Chamaeleon star-forming region and the ϵ Cha moving group, in particular for low-mass stars and substellar objects. We extended the search region significantly beyond the dark clouds.
Methods: Our sample has been selected based on proper motions and colours obtained from Gaia and 2MASS. We present and discuss the optical spectroscopic follow-up of 18 low-mass stellar objects in Cha I and ϵ Cha. We characterize the properties of objects by deriving their physical parameters from spectroscopy and photometry.
Results: We add three more low-mass members to the list of Cha I and increase the census of known ϵ Cha members by more than 40%, thereby spectroscopically confirming 13 new members and relying on X-ray emission as youth indicator for 2 more. In most cases the best-fitting spectral template is from objects in the TW Hya association, indicating that ϵ Cha has a similar age. The first estimate of the slope of the initial mass function in ϵ Cha down to the substellar regime is consistent with that of other young clusters. We estimate our initial mass function (IMF) to be complete down to ≈0.03 M_⊙. The IMF can be represented by two power laws: for M < 0.5 M_⊙ α = 0.42 ± 0.11 and for M > 0.5 M_⊙ α = 1.44 ± 0.12.
Conclusions: We find similarities between ϵ Cha and the southernmost part of Lower Centaurus Crux (LCC A0), which lie at similar distances and share the same proper motions. This suggests that ϵ Cha and LCC A0 may have been born during the same star formation event