A SUBMILLIMETER STUDY OF THE CLASS-0 PROTOSTAR HH24MMS

Results are presented of a JCMT submillimetre continuum study of the r ecently discovered candidate protostellar source HH24MMS. New submilli metre flux densities are listed, which were obtained under good weathe r conditions on Mauna Kea, and the shortest wavelength detection of th is source is now 350 mu m. The spectrum of HH24MMS is discussed and it s implications for the mass, luminosity and evolutionary stage of the source are derived under two different sets of assumptions: (i) a grey -body single-temperature fit to the submillimetre spectral energy dist ribution, and (ii) a radiative transfer calculation with a dust model of icy and fluffy grains and a radial temperature dependence. A VLA co ntinuum source coincident with the submillimetre source indicates an e mbedded young stellar object, and hence a protostellar source which ha s passed the ambipolar diffusion phase; the radio spectral index shows the emission to be partly free-free and partly thermal dust. A 450-mu m map of HH24MMS shows the source to be unresolved E-W, and partially resolved N-S, with a deconvolved FWHM of 21 arcsec. The total mass of HH24MMS under this Gaussian is found to be similar to 4-9 M. under th e single-temperature assumption, and similar to 4-8 M. under the radia tive transfer model assumptions, consistent with virial mass estimates from (CO)-O-18 linewidths. If the higher values are correct, they may be indicating partial gas freezing on to dust grains. Because of the absence of far-IR data the total luminosity is still uncertain. We can place an upper limit of 20 L. from the IRAS upper limits. The single- temperature assumption yields a best estimate of the total luminosity of 5.3 L.. The radiative transfer model attempts to separate the two c ontributions to this luminosity of external heating and internal heati ng, and suggests an upper limit to the luminosity of the central proto stellar source of 2.5 L.. We use the ratio of total to submillimetre l uminosity to determine the appropriate classification of a young stell ar object, finding a value of this ratio for this source of <40, well below the Class 0 upper limit of 200. Hence we confirm that HH24MMS is a Class 0 protostar, which is at the beginning of the protostellar ac cretion phase.