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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($J=5-4$) spectraldata 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. Thedata were obtained toward the cyanopolyyne peak with $\sim$30 hours integrationusing the Z45 receiver and the PolariS spectrometer installed in the Nobeyama45m telescope. Analyses of the optically thin $F=4-4$ and $5-5$ hyperfine linesof the HC$_3$N emission show that the spectra consist of four distinct velocitycomponents with a small line width ($\lesssim 0.1$ km s$^{-1}$) at $V_{\rmLSR}=$5.727, 5.901, 6.064, and 6.160 km s$^{-1}$, which we call A, B, C, and D,respectively, in the order of increasing LSR velocities. Utilizing the velocityinformation of the four velocity components, we further analyzed the opticallythicker CCS spectrum and the other hyperfine lines of the HC$_3$N emission bysolving the radiative transfer to investigate how the four velocity componentsoverlap along the line of sight. Results indicate that they are located in theorder of A, B, C, and D from far side to near side to the observer, indicatingthat TMC-1 is shrinking, moving inward as a whole.

Spectral Tomography for the Line-of-Sight Structures of the Taurus Molecular Cloud 1