New low-mass members of Chamaeleon I and $\epsilon$ Cha

TL;DR

This study expands the known low-mass star and substellar object membership in the Chamaeleon I region and $oldsymbol{ ext{epsilon}}$ Cha group, characterizing their properties and initial mass function, and suggesting a common origin with LCC A0.

Contribution

It provides new low-mass members for Chamaeleon I and $oldsymbol{ ext{epsilon}}$ Cha, estimates the IMF down to 0.03 M$_{ ext{sun}}$, and explores their possible shared formation history.

Findings

Added three low-mass members to Chamaeleon I.

Increased $oldsymbol{ ext{epsilon}}$ Cha membership by over 40%.

IMF slope consistent with other young clusters.

Abstract

The goal of this paper is to increase the membership list of the Chamaeleon star forming region and the $\epsilon$ Cha moving group, in particular for low-mass stars and substellar objects. We extended the search region significantly beyond the dark clouds. 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 $\epsilon$ Cha. We characterize the properties of objects by deriving their physical parameters, both from spectroscopy and photometry. We add three more low-mass members to the list of Cha I, and increase the census of known $\epsilon$ Cha members by more than 40%, confirming spectroscopically 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 $\epsilon$ Cha has a similar age. The first estimate of the slope of the initial mass function in $\epsilon$ Cha down to the sub-stellar regime is consistent with that of other young clusters. We estimate our IMF to be complete down to $\approx 0.03$M$_{\odot}$. The IMF can be represented by two power laws: for M $<$ 0.5 M$_{\odot}$ $\alpha = 0.42 \pm 0.11$ and for M $>$ 0.5 M$_{\odot}$ $\alpha = 1.44 \pm 0.12$. We find similarities between $\epsilon$ Cha and the southernmost part of Lower Centaurus Crux (LCC A0), both lying at similar distances and sharing the same proper motions. This suggests that $\epsilon$ Cha and LCC A0 may have been born during the same star formation event