The Corona-Australis star-forming region

Abstract

Context. The star-forming complex of Corona Australis (CrA) is one of the closest and most isolated molecular clouds. It belongs to a chain of clusters that show age gradients with distance from the galactic plane.Aims. We aim to provide suggestions regarding its formation history by examining the stellar and disk populations, the stellar multiplicity, and the interstellar absorption.Methods. We made a census of stars and disks using Gaia DR3 and infrared data. Interstellar absorption in the direction of each star was derived by comparing spectral types from the literature and Gaia colors. Stellar multiplicity analysis accounts for both direct observation of visual companions (Gaia data and high-contrast imaging) and indirect detection of the presence of companions (eclipsing binaries, spectroscopic binaries, and astrometry). The properties of the disks were obtained from the slopes of the spectral energy distributions.Results. As found in previous studies, the CrA complex can be divided into two regions: a younger region (CrA-Main: 3±1 Myr) and an older one (CrA-North: 6.7±0.3 Myr), which are slightly younger than previously thought. Moreover, while CrA-Main still appears bound to the gas, CrA-North is unbound and expanding. The stars that belong to CrA-North were in the most compact configuration 3.72 Myr ago. At that time, CrA-Main and CrA-North were also much closer to each other than they appear now. The fraction of disk-bearing stars is higher in CrA-Main than in CrA-North, as also expected due to the younger age of CrA-Main.Conclusions. We propose a formation history scenario for the CrA-complex. It started between 15 and 18 Myr ago with supernovae (SNe) explosions in the Upper Centaurus-Lupus complex, followed by a quiescent phase with little star formation. A star formation episode ~7 Myr ago formed CrA-North stars. About 3.7 Myr ago, a second SN explosion south of CrA-North triggered star formation in CrA-Main. This last SN might have been the origin of the pulsar RX J1856.5-3754.