TMRT OBSERVATIONS OF CARBON-CHAIN MOLECULES IN SERPENS SOUTH 1a

ABSTRACT We report Shanghai Tian Ma Radio Telescope (TMRT) detections of several long carbon-chain molecules in the C and Ku bands, including HC3N, HC5N, HC7N, HC9N, C3S, C6H, and C8H toward the starless cloud Serpens South 1a. We detected some transitions (HC9N J = 13-12, F = 12-11, and F = 14-13; H13CCCN J = 2-1, F = 1-0, and F = 1-1; HC13CCN J = 2-1, F = 2-2, F = 1-0, and F = 1-1; HCC13CN J = 2-1, F = 1-0, and F = 1-1) and resolved some hyperfine components (HC5N J = 6-5, F = 5-4; H13CCCN J = 2-1, F = 2-1) for the first time in the interstellar medium. The column densities of these carbon-chain molecules in the range 1012-1013 cm−2 are comparable to two carbon-chain molecule rich sources, TMC-1 and Lupus-1A. The abundance ratios are 1.00:(1.11 0.15):(1.47 0.18) for [H13CCCN]:[HC13CCN]:[HCC13CN]. This result implies that the 13C isotope is also concentrated in the carbon atom adjacent to the nitrogen atom in HC3N in Serpens South 1a, which is similar to TMC-1. The [HC3N]/[H13CCCN] ratio of 78 9, the [HC3N]/[HC13CCN] ratio of 70 8, and the [HC3N]/[HCC13CN] ratio of 53 4 are also comparable to those in TMC-1. Serpens South 1a proves to be a suitable testing ground for understanding carbon-chain chemistry.