Chemical segregation in the young protostars Barnard 1b-N and S: evidence of pseudo-disk rotation in Barnard

Abstract

The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40″ × 70″ images of Barnard 1b in the CO 1 → 0, CO 1 → 0, NHD 1a→ 1s, and SO 3→ 2 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of ~500 au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of ~0.2-0.4 m s au in the east-west direction, reminiscent of an axial collapse. The NHD data reveal cold and dense pseudo-disks (R ~ 500-1000 au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in HCO and CHOH, in any of the imaged species. The non-detection of SO constrains the SO/CHOH abundance ratio in the high-velocity gas.