The Nearby, Young, Chi1 Fornacis Cluster: Membership, Age, and an Extraordinary Ensemble of Dusty Debris Disks

TL;DR

This study characterizes the nearby Chi1 Fornacis cluster's membership, age (~40 Myr), and structure, revealing an extraordinary prevalence of dusty debris disks around M-type stars, and its relation to other stellar groups.

Contribution

It provides the first detailed analysis of the Chi1 Fornacis cluster's properties and its unique dusty debris disk phenomenon among M-type stars.

Findings

Cluster is ~40 Myr old at 104 pc distance.

High percentage of M-type stars with warm dust disks.

Chi1 For is related to Tucana-Horologium and Columba groups.

Abstract

Only four star clusters are known within ~100 pc of Earth. Of these, the Chi1 For cluster has barely been studied. We use the Gaia DR2 catalog and other published data to establish the cluster membership, structure, and age. The age of and distance to the cluster are ~40 Myr and 104 pc, respectively. A remarkable, unprecedented, aspect of the cluster is the large percentage of M-type stars with warm excess infrared emission due to orbiting dust grains -- these stars lie in an annulus that straddles the tidal radius of the cluster. The Chi1 For cluster appears to be closely related to two extensive, previously known, groups of co-moving, coeval stars (the Tucana-Horologium and Columba Associations) that are spread over much of the southern sky. While Tuc-Hor and Chi1 For are comoving and coeval, the difference in the frequency of their warm dusty debris disks at M-type stars could hardly be more dramatic.