Carbon Chain Molecules Toward Embedded Low-Mass Protostars

Abstract

Carbon chain molecules may be an important reservoir of reactive organics during star and planet formation. Carbon chains have been observed toward several low-mass young stellar objects (YSOs), but their typical abundances and chemical relationships in such sources are largely unconstrained. We present a carbon chain survey toward 16 deeply embedded (Class 0/I) low-mass protostars made with the IRAM 30 m telescope. Carbon chains are found to be common at this stage of protostellar evolution. We detect CCS, CCCS, HC$_3$N, HC$_5$N, l-C$_3$H, and C$_4$H toward 88%, 38%, 75%, 31%, 81%, and 88% of sources, respectively. Derived column densities for each molecule vary by one to two orders of magnitude across the sample. As derived from survival analysis, median column densities range between 1.2$\times 10^{11}$ cm$^{-2}$ (CCCS) and 1.5$\times 10^{13}$ cm$^{-2}$ (C$_4$H) and estimated fractional abundances with respect to hydrogen range between 2$\times 10^{-13}$ (CCCS) and 5$\times 10^{-11}$ (C$_4$H), which are low compared to cold cloud cores, warm carbon chain chemistry (WCCC) sources, and protostellar model predictions. We find significant correlations between molecules of the same carbon chain families, as well as between the cyanpolyynes (HC$_{\rm n}$N) and the pure hydrocarbon chains (C$_{\rm n}$H). This latter correlation is explained by a closely-related production chemistry of C$_{\rm{n}}$H and cyanpolyynes during low-mass star formation.