An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud. II. CCS and HC7N Chemistry and Three Modes of Star Formation in the Filaments

Abstract

We present deep CCS and HC7N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100 m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J(N) = 2(1)-1(0) and HC7N J = 21-20 with a spectral resolution of 0.038 km s(-1) and an angular resolution of 31" We observed strong CCS emission in both evolved and young regions and weak emission in two evolved regions. HC7N emission is observed only in L1495A-N and L1521D. We find that CCS and HC7N intensity peaks do not coincide with NH3 or dust continuum intensity peaks. We also find that the fractional abundance of CCS does not show a clear correlation with the dynamical evolutionary stage of dense cores. Our findings and chemical modeling indicate that the fractional abundances of CCS and HC7N are sensitive to the initial gas-phase C/O ratio, and they are good tracers of young condensed gas only when the initial C/O is close to solar value. Kinematic analysis using multiple lines, including NH3, HC7N, CCS, CO, HCN, and HCO+, suggests that there may be three different star formation modes in the L1495-B218 filaments. At the hub of the filaments, L1495A/B7N has formed a stellar cluster with large-scale inward flows (fast mode), whereas L1521D, a core embedded in a filament, is slowly contracting because of its self-gravity (slow mode). There is also one isolated core that appears to be marginally stable and may undergo quasi-static evolution (isolated mode).