Kim 3: an Ultra-faint Star Cluster in the Constellation of Centaurus

TL;DR

This paper reports the discovery of Kim 3, an ultra-faint, compact star cluster in Centaurus, notable for being the least luminous known, with signs of ongoing tidal disruption and a relatively young, metal-poor stellar population.

Contribution

It presents the first detailed characterization of Kim 3, a newly discovered ultra-faint star cluster, highlighting its unique properties and evidence of tidal disruption.

Findings

Kim 3 is the least luminous star cluster known.

It shows signs of being in the final stage of tidal disruption.

Kim 3 has a relatively young and metal-poor stellar population.

Abstract

We report the discovery of an ultra-faint star cluster in the constellation of Centaurus. This new stellar system, Kim 3, features a half light radius of $r_{h}=2.29^{+1.28}_{-0.52}$ pc and a total luminosity of $M_{V}=+0.7\pm0.3$. Approximately 26 stars are identified as candidate member stars down to four magnitudes below the main-sequence turn-off, which makes Kim 3 the least luminous star cluster known to date. The compact physical size and extreme low luminosity place it close to faint star clusters in the size-luminosity plane. The stellar population of Kim 3 appears to be relatively young ($9.5^{+3.0}_{-1.7}$ Gyr) and metal-poor ([Fe/H]$=-1.6^{+0.45}_{-0.30}$) at a heliocentric distance of $15.14^{+1.00}_{-0.28}$ kpc. The cluster lacks a well-defined center and a small but prominent group of stars consistent with the Kim 3 isochrone is present approximately 9.7 pc in projection south of the cluster center. Both are signs of the cluster being in the final stage of tidal disruption.