The SOFIA Massive (SOMA) Star Formation Q-band follow-up I. Carbon-chain chemistry of intermediate-mass protostars

Kotomi Taniguchi; Prasanta Gorai; Jonathan C. Tan; Miguel Gomez-Garrido; Ruben Fedriani; Yao-Lun Yang; T. K. Sridharan; Kei Tanaka; Masao Saito; Yichen Zhang; Lawrence Morgan; Giuliana Cosentino; Chi-Yan Law

doi:10.1051/0004-6361/202451499

paper

The SOFIA Massive (SOMA) Star Formation Q-band follow-up I. Carbon-chain chemistry of intermediate-mass protostars

arXiv:2410.23392 · doi:10.1051/0004-6361/202451499

Abstract

Evidence for similar chemical characteristics around low- and high-mass protostars has been found: in particular, a variety of carbon-chain species and complex organic molecules (COMs) are formed around them. On the other hand, the chemical compositions around intermediate-mass (IM; $2 M_{⊙} < m_{*} < 8 M_{⊙}$ ) protostars have not been studied with large samples. In particular, it is unclear the extent to which carbon-chain species are formed around them. We aim to obtain the chemical compositions, particularly focusing on carbon-chain species, towards a sample of IM protostars. We have conducted Q-band (31.5-50 GHz) line survey observations towards eleven mainly intermediate-mass protostars with the Yebes 40 m radio telescope. The target protostars were selected from a sub-sample of the source list of the SOFIA Massive (SOMA) Star Formation project. Nine carbon-chain species (HC $_{3}$ N, HC $_{5}$ N, C $_{3}$ H, C $_{4}$ H, $l in e a r -$ H $_{2}$ CCC, $cy c l i c -$ C $_{3}$ H $_{2}$ , CCS, C $_{3}$ S, and CH $_{3}$ CCH), three COMs (CH $_{3}$ OH, CH $_{3}$ CHO, and CH $_{3}$ CN), H $_{2}$ CCO, HNCO, and four simple sulfur (S)-bearing species ( $^{13}$ CS, C $^{34}$ S, HCS $^{+}$ , H $_{2}$ CS) have been detected. The rotational temperatures of HC $_{5}$ N are derived to be $\sim 20 - 30$ K in three IM protostars and they are very similar compared to those around low- and high-mass protostars. These results indicate that carbon-chain molecules are formed in lukewarm ( $\sim 20 - 30$ K) gas around the IM protostars by the Warm Carbon-Chain Chemistry (WCCC) process. Carbon-chain formation occurs ubiquitously in the warm gas around protostars across a wide range of stellar masses. Carbon-chain molecules and COMs coexist around most of the target IM protostars, which is similar to the situation in low- and high-mass protostars. The chemical characteristics around protostars are common in the low-, intermediate- and high-mass regimes.

Accepted for publication in the Astronomy and Astrophysics (A&A)