Molecular Gas and Dust in the Massive Star Forming Region S 233 IR

摘要

The massive star forming region S 233 IR is observed in the molecular lines CO J = 2-1, 3-2, NH_3 (1,1), (2,2) and the 870 μm dust continuum. Four submillimeter continuum sources, labelled SMM 1-4, are revealed in the 870 μm dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2 coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32 K and 92 K for the cold- and hot-dust components. An SMM1 core mass of 246 solar mass and a total mass of 445 solar mass are estimated from the 870 μm dust continuum emission. SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3-2 emission is estimated to be 35 solar mass. Low velocity outflows are also found in the NH_3 (1,1) emission. The non-thermal dominant NH_3 line width as well as the substantial core mass suggest that the SMM1 core is a "turbulent, massive dense core", in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.