Protostars, multiplicity, and disk evolution in the Corona Australis region: a Herschel Gould Belt Study

Context. The CrA region and the Coronet cluster form a nearby (138 pc), young (1-2 Myr) star-forming region that hosts a moderate population of Class I, II, and III objects. Aims. We study the structure of the cluster and the properties of the protostars and protoplanetary disks in the region. Methods. We present Herschel PACS photometry at 100 and 160 mu m, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members within the cloud with high sensitivity and high dynamic range. Results. Many of the cluster members are detected, including some embedded, very low-mass objects, several protostars (some of them extended), and substantial emission from the surrounding molecular cloud. Herschel also reveals some striking structures, such as bright filaments around the IRS 5 protostar complex and a bubble-shaped rim associated with the Class I object IRS 2. The disks around the Class II objects display a wide range of mid-and far-IR excesses consistent with different disk structures. We have modeled the disks with the RADMC radiative transfer code to quantify their properties. Some of them are consistent with flared, massive, relatively primordial disks (S CrA, T CrA). Others display significant evidence for inside-out evolution, consistent with the presence of inner holes/gaps (G-85, G-87). Finally, we found disks with a dramatic small dust depletion (G-1, HBC 677) that, in some cases, could be related to truncation or to the presence of large gaps in a flared disk (CrA-159). The derived masses for the disks around the low-mass stars are found to be below the typical values in Taurus, in agreement with previous Spitzer observations. Conclusions. The Coronet cluster presents itself as an interesting compact region that contains both young protostars and very evolved disks. The Herschel data provide sufficient spatial resolution to detect small-scale details, such as filamentary structures or spiral arms associated with multiple star formation. The disks around the cluster members range from massive, flared primordial disks to disks with substantial small dust grain depletion or with evidence of inside-out evolution. This results in an interesting mixture of objects for a young and presumably coevally formed cluster. Given the high degree of multiplicity and interactions observed among the protostars in the region, the diversity of disks may be a consequence of the early star formation history, which should also be taken into account when studying the disk properties in similar sparsely populated clusters.