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Description
The Barnard 1b core shows signatures of being at the earliest stages of low- mass star formation, with two extremely young and deeply embedded proto- stellar objects. Hence, this core is an ideal target to study the structure and chemistry of the first objects formed in the collapse of prestellar cores. We present ALMA Band 6 spectral line observations at ~0.6" of angular resolution towards Barnard 1b. We have extracted the spectra towards both protostars, and used a local thermodynamic equilibrium (LTE) model to reproduce the observed line profiles. B1b-S shows rich and complex spectra, with emission from high energy transitions of complex molecules, such as CH_3_OCOH and CH_3_CHO, including vibrational level transitions. We have tentatively detected for the first time in this source emission from NH_2_CN, NH_2_CHO, CH_3_CH_2_OH, CH_2_OHCHO, CH_3_CH_2_OCOH and both aGg' and gGg' conformers of (CH_2_OH)_2_. This is the first detection of ethyl formate (CH_3_CH_2_OCOH) towards a low-mass star forming region. On the other hand, the spectra of the FHSC candidate B1b-N are free of COMs emission. In order to fit the observed line profiles in B1b-S, we used a source model with two components: an inner hot and compact component (200K, 0.35") and an outer and colder one (60K, 0.6"). The resulting COM abundances in B1b-S range from 10^-13^ for NH_2_CN and NH_2_CHO, up to 10^-9^ for CH_3_OCOH. Our ALMA Band 6 observations reveal the presence of a compact and hot component in B1b-S, with moderate abundances of complex organics. These results indicate that a hot corino is being formed in this very young Class 0 source.
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