Two Extreme Young Objects in Barnard 1-b

Abstract

Two submm/mm sources in the Barnard 1b (B1-b) core, B1-bN and B1-bS, have been studied in dust continuum, H13CO+ J=1-0, CO J=2-1, 13CO J=2-1, and C18O J=2-1. The spectral energy distributions of these sources from the mid-IR to 7 mm are characterized by very cold temperatures of T_dust < 20 K and low bolometric luminosities of 0.15-0.31 L_sun. The internal luminosities of B1-bN and B1-bS are estimated to be <0.01-0.03 L_sun and ~0.1-0.2 L_sun, respectively. Millimeter interferometric observations have shown that these sources have already formed central compact objects of ~100 AU sizes. Both B1-bN and B1-bS are driving the CO outflows with low characteristic velocities of ~2-4 km/s. The fractional abundance of H13CO+ at the positions of B1-bN and B1-bS is lower than the canonical value by a factor of 4-8. This implies that significant fraction of CO is depleted onto dust grains in dense gas surrounding these sources. The observed physical and chemical properties suggest that B1-bN and B1-bS are in the earlier evolutionary stage than most of the known Class 0 protostars. Especially, the properties of B1-bN agree with those of the first hydrostatic core predicted by the MHD simulations. The CO outflow was also detected in the mid-IR source located at ~15" from B1-bS. Since the dust continuum emission was not detected in this source, the circumstellar material surrounding this source is less than 0.01 M_sun. It is likely that the envelope of this source was dissipated by the outflow from the protostar that is located to the southwest of B1-b.