Protostars and stars in the Coronet cluster: Age, evolution, and cluster structure

TL;DR

This study combines optical, near-IR, and submillimeter observations to determine that the Coronet cluster is younger than 2 million years, revealing details about its structure, star formation activity, and disk evolution.

Contribution

It provides a revised, younger age estimate for the Coronet cluster based on new multi-wavelength data and analyzes its structure and star formation characteristics.

Findings

Cluster age estimated at ~0.5-1 Myr

Star formation occurs in two elongated structures

Low disk and accretion fraction observed

Abstract

We present new optical spectroscopy with FLAMES/VLT, near-IR imaging with HAWK-I/VLT, and 870 micron mapping with APEX/LABOCA of the Coronet cluster. The optical data allow to estimate spectral types, extinction and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in the HR diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably ~0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks.