Revealing the Chamaeleon: First detection of a low-mass stellar halo around the young open cluster Eta Chamaeleontis

TL;DR

This study discovers a low-mass stellar halo around Eta Chamaeleontis, expanding the known cluster boundary, and suggests a dynamical origin for its current structure based on new member identification and variability analysis.

Contribution

It reports the first detection of a low-mass stellar halo around Eta Chamaeleontis and proposes a dynamical formation scenario without requiring an unusual initial mass function.

Findings

Identification of several lithium-rich low-mass stars beyond previous search radius

Detection of variability in H-alpha emission indicating active accretion

Proposal of a dynamical origin for the cluster's current configuration

Abstract

We have identified several lithium-rich low-mass (0.08<M<0.3 Msun). stars within 5.5 deg of the young open cluster Eta Chamaeleontis, nearly four times the radius of previous search efforts. We propose 4 new probable cluster members and 3 possible members requiring further investigation. Candidates were selected on the basis of DENIS and 2MASS photometry, NOMAD astrometry and extensive follow-up spectroscopy. Several of these stars show substantial variation in their H-alpha emission line strengths on timescales of days to months, with at least one event attributable to accretion from a circumstellar disk. These findings are consistent with a dynamical origin for the current configuration of the cluster, without the need to invoke an abnormally top-heavy Initial Mass Function, as proposed by some authors.