The JCMT Gould Belt Survey: First results from the Corona Australis molecular cloud and evidence of variable dust emissivity indices in the Coronet region

Abstract

We present 450 m and 850 m James Clerk Maxwell Telescope (JCMT) observations of the Corona Australis (CrA) molecular cloud taken as part of the JCMT Gould Belt Legacy Survey (GBLS). We present a catalogue of 39 starless and protostellar sources, for which we determine source temperatures and masses using SCUBA-2 450 m/850 m flux density ratios for sources with reliable 450 m detections, and compare these to values determined using temperatures measured by the Herschel Gould Belt Survey (HGBS). In keeping with previous studies, we find that SCUBA-2 preferentially detects high-volume-density starless cores, which are most likely to be prestellar (gravitationally bound). We do not observe any anti-correlation between temperature and volume density in the starless cores in our sample. Finally, we combine our SCUBA-2 and Herschel data to perform SED fitting from 160–850 m across the central Coronet region, thereby measuring dust temperature T, dust emissivity index β and column density N(H2) across the Coronet. We find that β varies across the Coronet, particularly measuring β = 1.55 ± 0.35 in the colder starless SMM-6 clump to the north of the B star R CrA. This relatively low value of β is suggestive of the presence of large dust grains in SMM-6, even when considering the effects of T − β fitting degeneracy and 12CO contamination of SCUBA-2 850 m data on the measured β values.