Long Carbon Chains in the Warm Carbon-chain-chemistry Source L1527: First Detection of C₇H in Molecular Clouds

Abstract

Abstract Long carbon-chain molecules were searched for toward the low-mass star-forming region L1527, which is a prototypical source of warm carbon-chain chemistry (WCCC), using the 100 m Green Bank Telescope. Long carbon-chain molecules, C 7 H ( 2 Π 1/2 ), C 6 H ( 2 Π 3/2 and 2 Π 1/2 ), CH 3 C 4 H, and C 6 H 2 (cumulene carbene, CCCCCCH 2 ), and cyclic species of C 3 H and C 3 H 2 O were detected. In particular, C 7 H was detected for the first time in molecular clouds. The column density of C 7 H is determined to be 6 × 10 10 cm −2 . The column densities of the carbon-chain molecules including CH 3 C 4 H and C 6 H in L1527 relative to those in the starless dark cloud Taurus Molecular Cloud-1 Cyanopolyyne Peak (TMC-1 CP) tend to be systematically lower for long carbon-chain lengths. However, the column densities of C 7 H and C 6 H 2 do not follow this trend and are found to be relatively abundant in L1527. This result implies that these long carbon-chain molecules are remnants of the cold starless phase. The results—that both the remnants and WCCC products are observed toward L1527—are consistent with the suggestion that the protostar can also be born in the parent core at a relatively early stage in the chemical evolution.