The very low-mass population of the Corona Australis and Chamaeleon II star forming regions

¹ Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain e-mail: blopez@am.ub.es
² Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany e-mail: jochen@tls-tautenburg.de
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: mundt@mpia-hd.mpg.de

Received: 18 May 2005
Accepted: 21 July 2005

Abstract

We present the results of a deep optical survey in the Corona Australis and Chamaeleon II star forming regions. Our optical photometry is combined with available near- and mid-infrared photometry to identify very low-mass candidate members in these dark clouds. In our Chamaeleon II field, only one object exhibits clear Hα emission, but the discrepancy between its optical and near-infrared colours suggests that it might be a foreground star. We also identify two objects without Hα emission that could be planetary mass members of Chamaeleon II. In Corona Australis, we find ten stars and three brown dwarf candidates in the Coronet cluster. Five of our new members are identified with ISOCAM sources. Only two of them have a mid-infrared excess, indicating the presence of an accretion disk. On the other hand, one brown dwarf candidate has a faint close companion, seen only in our deepest I-band image. For many of the candidates in both clouds, membership could not be inferred from their Hα emission or near-infrared colours; these objects need spectroscopic confirmation of their status.