Spectral Tomography for the Line-of-Sight Structures of the Taurus
  Molecular Cloud 1
  We clarify the line-of-sight structure of the Taurus Molecular Cloud 1
(TMC-1) on the basis of the CCS($J_N=4_3-3_2$) and HC$_3$N($J=5-4$) spectral
data observed at a very high velocity resolution and sensitivity of $\Delta V
\simeq 0.0004$ km s$^{-1}$ ($=61$ Hz) and $\Delta T_{\rm mb} \simeq 40$ mK. The
data were obtained toward the cyanopolyyne peak with $\sim$30 hours integration
using the Z45 receiver and the PolariS spectrometer installed in the Nobeyama
45m telescope. Analyses of the optically thin $F=4-4$ and $5-5$ hyperfine lines
of the HC$_3$N emission show that the spectra consist of four distinct velocity
components with a small line width ($\lesssim 0.1$ km s$^{-1}$) at $V_{\rm
LSR}=$5.727, 5.901, 6.064, and 6.160 km s$^{-1}$, which we call A, B, C, and D,
respectively, in the order of increasing LSR velocities. Utilizing the velocity
information of the four velocity components, we further analyzed the optically
thicker CCS spectrum and the other hyperfine lines of the HC$_3$N emission by
solving the radiative transfer to investigate how the four velocity components
overlap along the line of sight. Results indicate that they are located in the
order of A, B, C, and D from far side to near side to the observer, indicating
that TMC-1 is shrinking, moving inward as a whole.
