Far-infrared observations of three compact IRAS sources in Sh 247 star forming complex: IRAS 06056+2131, 06058+2138 and 06061+2151

Abstract

Three compact IRAS sources-IRAS 06056+2131, 06058+2138 and 06061+2151 in the Sh 247 complex and having IRAS colours typical of compact H II regions have been observed in the far-infrared using the TIFR 1 m balloon-borne telescope. The observations were done simultaneously in two bands; from these intensity maps at 58 μm and 150 μm with a spatial resolution of 1.'5 have been obtained. We have also obtained intensity maps in the four IRAS bands of 12, 25, 60 and 100 μm using the HIRES routine. Using these and other available observations the spectral energy distributions (SED) for the three sources have been obtained. Radiation transfer modelling has been undertaken to fit the observed SED and infer the nature and distribution of dust in the envelope. In particular, we find that a r⁻² density distribution is ruled out. The uniform density fits better for two sources while r⁻¹ distribution is better for the third. The total luminosities of the sources imply spectral types in the range O9 to B0; however, only two of them have been detected in the radio continuum, that too at a level much lower than that expected. All three are presumably optically thick at 3.6 cm. Molecular observations available in the lines of CO, CS, NH₃ etc. show dense molecular cores as well as outflows associated with all the three sources. IRAS 06056+2131 shows an extended structure with two cores while IRAS 06061+2151 has probably an additional core. The corresponding structures are also seen in the 25 μm map which has higher resolution. While all the three sources are very young and deeply embedded, the absence of radio continuum and non-fragmentation of the cloud suggest that IRAS 06058+2138 is the youngest of the three.