Abstract
Context. Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet. Aims. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis. Methods. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128 deg2 around the dark clouds of the region. Results. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before. Our sample of members covers the magnitude range between G ≳ 5 mag and G ≲ 20 mag, and it reveals the existence of two kinematically and spatially distinct subgroups. There is a distributed “off-cloud” population of stars located in the north of the dark clouds that is twice as numerous as the historically known “on-cloud” population that is concentrated around the densest cores. By comparing the location of the stars in the HR-diagram with evolutionary models, we show that these two populations are younger than 10 Myr. Based on their infrared excess emission, we identify 28 Class II and 215 Class III stars among the sources with available infrared photometry, and we conclude that the frequency of Class II stars (i.e. “disc-bearing” stars) in the on-cloud region is twice as large as compared to the off-cloud population. The distance derived for the Corona-Australis region based on this updated census is d = 149.4 +0.4−0.4 pc, which exceeds previous estimates by about 20 pc. Conclusions. In this paper we provide the most complete census of stars in Corona-Australis available to date that can be confirmed with Gaia data. Furthermore, we report on the discovery of an extended and more evolved population of young stars beyond the region of the dark clouds, which was extensively surveyed in the past.
Highlights
In the early 1960s, Herbig (1960) estimated the age of the two variable stars R CrA and T CrA associated with nebulosity based on the expected time required for them to contract to the main sequence (∼107 yr) and showed that they were young
To perform the membership analysis described in this paper, we downloaded the Gaia-DR2 catalogue in the region defined by 0◦ ≤ l ≤ 4◦ and −26◦ ≤ b ≤ −10◦ as well as 356◦ ≤ l ≤ 360◦ and −26◦ ≤ b ≤ −10◦, which clearly extends beyond the location of the Coronet cluster and known young stellar objects (YSO) in the CoronaAustralis region
The remaining candidate members from the literature, which were rejected by our analysis, have proper motions and/or parallaxes in Gaia-DR2 that are inconsistent with membership in Corona-Australis, and they lie below or above the empirical isochrone defined by the cluster members
Summary
In the early 1960s, Herbig (1960) estimated the age of the two variable stars R CrA and T CrA associated with nebulosity based on the expected time required for them to contract to the main sequence (∼107 yr) and showed that they were young. The mean parallax of these stars ( = 6.8 ± 0.3 mas) yields a distance of 146 ± 6 pc and suggests that the adopted distance to CoronaAustralis needs to be revised In this context, the second data release of the Gaia space mission (Gaia-DR2, Gaia Collaboration 2018) allowed us to search for additional members in Corona-Australis and revisit the distance to this region. We discuss the existence of substructures in the Corona-Australis region, compute distances and 2D velocities for individual stars from Bayesian inference, and classify the newly discovered members as Class I, II, or III stars based on their infrared excess emission.
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