An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus
  Molecular Cloud: II CCS & HC$_7$N Chemistry and Three Modes of Star Formation
  in the Filaments
  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).
