eROSITA X-ray scan of the eta Chamaeleontis cluster

TL;DR

This study used eROSITA X-ray observations to analyze known and potential new members of the eta Chamaeleontis cluster, identifying additional dispersed members and characterizing their X-ray properties to understand the cluster's structure.

Contribution

First X-ray survey of eta Chamaeleontis with eROSITA, identifying new dispersed members and providing detailed X-ray properties of known and candidate cluster stars.

Findings

Identified five new stellar systems with similar X-ray characteristics to known members.

Confirmed four previously proposed members through X-ray data.

Estimated at least 23 total members, including dispersed halo population.

Abstract

The nearby young open cluster eta Chamaeleontis has been observed by eROSITA/SRG during its CalPV phase for 150 ks. The eROSITA data were taken in the field-scan mode, an observing mode of Spectrum-Roentgen-Gamma (SRG) that follows a rectangular grid-like pattern, here covering a 5x5 deg field with an exposure depth of about 5 ks. We study the known members in X-rays and search for potential new members of the anticipated dispersed low-mass cluster population. Detected sources were identified by cross-matching X-ray sources with Gaia and 2MASS, and young stars were identified by their X-ray activity, the position in the color-magnitude diagram, and by their astrometric and kinematic properties. X-ray-luminosities, light curves, and spectra of cluster members were obtained and compared with previous X-ray data. Literature results of other member searches were used to verify our new member candidates in the observed field. We determine X-ray properties of virtually all known eta Cha members and identify five additional stellar systems that show basically identical characteristics, but are more dispersed. Four of them were previously proposed as potential members; this status is supported by our X-ray study. Based on their spatial distribution, further members are expected beyond the sky region we surveyed. The identified stellar systems very likely belong to the ejected halo population, which brings the total number of eta Cha cluster members to at least 23.