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 HC 7 N observations of the L1495-B218 filaments in the Taurus molecular cloud obtained using the K-band focal plane array on the 100m Green Bank Telescope. We observed the L1495-B218 filaments in CCS J N = 2 1 −1 0 and HC 7 N 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. HC 7 N emission is observed only in L1495A-N and L1521D. We find that CCS and HC 7 N intensity peaks do not coincide with NH 3 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 HC 7 N 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 NH 3 , HC 7 N, CCS, CO, HCN, & 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), while L1521D, a core embedded in a filament, is slowly contracting due to 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).

Cyanoacetylene in the outflow/hot molecular core G331.512−0.103

“…4, we did not report evidences for HC5N, HC7N, nor HC9N (e.g. Sakai et al 2008;Jaber Al-Edhari et al 2017;Zhang et al 2017;Cordiner et al 2017;Mendoza et al 2018a;Seo et al 2019). The absence of HC5N in the current dataset could be associated with several factors, such as (1) insufficient sensitivity in the frequencies of the APEX-1 and APEX-2 data, (2) the excitation regime of the molecular environment, or (3) lower abundances of the molecule.…”

TRAO Survey of Nearby Filamentary Molecular Clouds, the Universal Nursery of Stars (TRAO FUNS). I. Dynamics and Chemistry of L1478 in the California Molecular Cloud

“…This indicates that the filamentary accretion flow as well as turbulent gas motions in the filament may play an important role in the formation of dense cores and stars. Seo et al (2019) investigated the kinematics and chemistry of star-forming regions in the Taurus molecular cloud, and proposed three star formation types, i.e., fast, slow, and isolated modes depending on the filamentary structures involved in the star formation. The fast mode may apply for star formation at the hub where 1) Y ( 0) Y ( 1) 5…”

A centrally concentrated sub-solar-mass starless core in the Taurus L1495 filamentary complex

“…However, our HCO + (1-0) observation of this core with the Nobeyama 45 m telescope shows single-peaked profiles through the observed region. Note that Seo et al (2019) also could not find collapsing motions in the HCN (1-0) and HCO + (1-0) profile toward this core although the lack of such evidence does not necessarily mean that there are no internal inflow motions. For example, the dynamically collapsing region is smaller than the beam size, < ∼ 3,000 au, and the observed filament is not collapsing as a whole.…”