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

We present 450 and 850 μm 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 μm/850 μm flux density ratios for sources with reliable 450 μm 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 anticorrelation 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 μm 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 μm data on the measured β values.