The Stellar Population of the Chamaeleon I Star-Forming Region

TL;DR

This study provides a comprehensive census of the Chamaeleon I star-forming region, discovering new members, analyzing their properties, and comparing the initial mass function with other clusters to understand star formation history.

Contribution

It presents the discovery of 50 new members, including many substellar objects, and analyzes their ages, masses, and spatial distribution using new photometry, spectroscopy, and evolutionary models.

Findings

226 known members including 14 substellar objects

Star formation began 3-6 million years ago with ongoing activity

IMF peaks at 0.1-0.15 solar masses and remains flat into the substellar regime

Abstract

I present a new census of the stellar population in the Chamaeleon I star-forming region. Using optical and near-IR photometry and followup spectroscopy, I have discovered 50 new members of Chamaeleon I, expanding the census of known members to 226 objects. Fourteen of these new members have spectral types later than M6, which doubles the number of known members that are likely to be substellar. I have estimated extinctions, luminosities, and effective temperatures for the known members, used these data to construct an H-R diagram for the cluster, and inferred individual masses and ages with the theoretical evolutionary models of Baraffe and Chabrier. The distribution of isochronal ages indicates that star formation began 3-4 and 5-6 Myr ago in the southern and northern subclusters, respectively, and has continued to the present time at a declining rate. The IMF in Chamaeleon I reaches a maximum at a mass of 0.1-0.15 M_sun, and thus closely resembles the IMFs in IC 348 and the Orion Nebula Cluster. In logarithmic units where the Salpeter slope is 1.35, the IMF is roughly flat in the substellar regime and shows no indication of reaching a minimum down to a completeness limit of 0.01 M_sun. The low-mass stars are more widely distributed than members at other masses in the northern subcluster, but this is not the case in the southern subcluster. Meanwhile, the brown dwarfs have the same spatial distribution as the stars out to a radius of 3 deg (8.5 pc) from the center of Chamaeleon I.