We study molecular emission in a massive condensation at the border of the HII region RCW 120, paying particular attention to the Core 1 and Core 2 objects, the most massive fragments of the condensation found previously by ALMA. The latter fragment was previously suggested to host a high-mass analogue of Class 0 young stellar object. We present spectra of molecular emission in the 1 mm range made with the APEX telescope. We detect CH3OH and C34S lines in Core 1 and Core 2. The CH3CN series and the SO2 lines are only found in Core 2. We estimate gas physical parameters using methanol lines and obtain gas temperature less than 100 K in both regions. Molecular hydrogen number density in Core 2 is in the range of 105−107 cm−3 and is more uncertain in Core 1. However, the detection of the CH3CN lines corresponding to highly excited transitions (Eu>400~K) in Core~2 indicates that the region contains hot gas, while the abundances of CH3OH, CS, SO2 and CH3CN are quite low for a hot core stage. We propose that Core 2 is in the warm-up phase prior to the establishing of the hot gas chemistry. We suggest that Core 2 is in the beginning of the hot core stage. There are no detected CH3CN lines in Core 1, therefore, it might be on an even less evolved evolutionary stage.
@article{arxiv.2102.09145,
title = {The warm-up phase in massive star-forming cores around RCW 120},
author = {M. S. Kirsanova and S. V. Salii and S. V. Kalenskii and D. S. Wiebe and A. M. Sobolev and P. A. Boley},
journal= {arXiv preprint arXiv:2102.09145},
year = {2021}
}