Corona-Australis is one of the closest regions to the Sun with recent and ongoing star formation.
Its stellar population has been extensively surveyed over the last decades, but only a small number of members could be effectively identified due to the high extinction and lack of accurate data (e.g. proper motions and parallaxes) which hampered many studies in the past. We have recently performed a membership analysis based on Gaia-DR2 data over a field of 128deg² around the dark clouds of the region and identified 313 high-probability members.
Our new census of the Corona-Australis population covers the magnitude range from G > 5 mag to G < 20 mag, and includes stars with masses ranging from 0.02 to 5 solar masses. We report 262 stars which had never been classified as members before, and we increase the number of stars in this region by a factor of about five.
In particular, we discovered a more dispersed “off-cloud” population of stars in the north of the molecular clouds that is twice as numerous as the “on-cloud” population of stars which is located mostly in the densest cores of the region and contains most of the classical members identified in the past (see Figure 1). The two populations exhibit slightly distinct properties (see Figure 2), but they are very close to each other and part of the same star-forming complex. Our study also returned a new distance determination of 149.4 ± 0.4 pc for the Corona-Australis region that exceeds previous estimates by about 20pc. Altogether, this shows that the Corona-Australis region hosts one of the richest association of T Tauri stars of the Solar neighbourhood making it a promising target for many studies related to star and planet formation.
Figure 1: Location of the high-probability members of the Corona-Australis star-forming region identified in our analysis. Red and blue symbols indicate the “off-cloud” and “on-cloud” populations of stars investigated in our study.
Figure 2: Proper motions and parallaxes of the two populations of stars in Corona-Australis.
© Last Update: 03-11-2020 by H. Bouy