The warm-up phase in massive star-forming cores around RCW 120

Abstract

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 CH${}_3$OH and C${}^{34}$S lines in Core 1 and Core 2. The CH${}_3$CN series and the SO${}_2$ 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 $10^5-10^7$ cm${}^{-3}$ and is more uncertain in Core 1. However, the detection of the CH${}_3$CN lines corresponding to highly excited transitions ($E_{\mathrm{u}}>400$~K) in Core~2 indicates that the region contains hot gas, while the abundances of CH${}_3$OH, CS, SO${}_2$ and CH${}_3$CN 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 CH${}_3$CN lines in Core 1, therefore, it might be on an even less evolved evolutionary stage.

arXiv comment11 pages, 6 figures, accepted by MNRAS

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Cited by in corpus (6)

• The Role of Magnetic Fields in Triggered Star Formation of RCW 120
• The methanol emission in the $J_1-J_0$ A${}^{-+}$ line series as a tracer of specific physical conditions in high-mass star-forming regions
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