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Post Info TOPIC: Barnard 1b
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RE: Barnard 1b
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Title: Two Extreme Young Objects in Barnard 1-b
Author: Naomi Hirano, Fang-Chun Liu

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.

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Blobrana


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Title: Probing the Earliest Stage of Protostellar Evolution -- Barnard 1-bN and Barnard 1-bS
Authors: Yun-Hsin Huang, Naomi Hirano

Two submm/mm sources in the Barnard 1b (B1-b) core, B1-bN and B1-bS, have been observed with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The 1.1 mm continuum map obtained with the SMA reveals that the two sources contain spatially compact components, suggesting that they harbour protostars. The N2D+ and N2H+ J=3-2 maps were obtained by combining the SMA and SMT data. The N2D+ map clearly shows two peaks at the continuum positions. The N2H+ map also peaks at the continuum positions, but is more dominated by the spatially extended component. The N2D+/N2H+ ratio was estimated to be ~ 0.2 at the positions of both B1-bN and B1-bS. The derived N2D+/N2H+ ratio is comparable to those of the prestellar cores in the late evolutionary stage and the class 0 protostars in the early evolutionary stage. Although B1-bN is bright in N2H+ and N2D+, this source was barely seen in H13CO+. This implies that the depletion of carbon-bearing molecules is significant in B1-bN. The chemical property suggests that B1-bN is in the earlier evolutionary stage as compared to B1-bS with the H13CO+ counterpart. The N2H+ and N2D+ lines show that the radial velocities of the two sources are different by ~ 0.9 km s-1. However, the velocity pattern along the line through B1-bN and B1-bS suggests that these two sources were not formed out of a single rotating cloud. It is likely that the B1-b core consists of two velocity components, each of which harbours a very young source.

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