Chemical segregation in the young protostars Barnard 1b-N and S

Evidence of pseudo-disk rotation in Barnard 1b-S^⋆,⋆⋆

¹ Observatorio Astronómico Nacional (OAN, IGN), Apdo 112, 28803 Alcalá de Henares, Spain
e-mail: a.fuente@oan.es
² LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, École Normale Supérieure, 75005 Paris, France
³ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’ Hères, France
⁴ Centre de Recherche Astronomique de Lyon (CRAL), École Normale Supérieure de Lyon, CNRS-UMR 5574, 69364 Lyon Cedex 07, France
⁵ Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC). 28049 Cantoblanco, Madrid, Spain
⁶ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA

Received: 10 April 2017
Accepted: 18 August 2017

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 ¹³CO 1 → 0, C¹⁸O 1 → 0, NH₂D 1_1,1a→ 1_0,1s, and SO 3₂→ 2₁ 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^-1 au^-1 in the east-west direction, reminiscent of an axial collapse. The NH₂D 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 H₂CO and CH₃OH, in any of the imaged species. The non-detection of SO constrains the SO/CH₃OH abundance ratio in the high-velocity gas.