L1521E: A starless core in the early evolutionary stage?

We have studied the physical and chemical properties of a quiescent starless core L1521E with various molecular lines. We found that there exists a compact dense core traced by the (HCO+)-C-13, (HNC)-C-13, CCS, and HC3N lines; their distributions have a single peak at the same position. The core radius is as small as 0.031 pc, whereas the H-2 density at the peak position is as high as (1.3-5.6) x 10(5) cm(-3). Although the density is high enough to excite the inversion transitions of NH3, these lines are found to be very faint in L1521E. The distributions of NH3 and CCS seem to be different from those of well-studied starless cores, L1498 and L1544, where the distribution of CCS shows a shell-like structure, while that of NH3 is concentrated at the center of the core. Abundances of carbon-chain molecules are higher in L1521E than in the other dark cloud cores; in particular, those of sulfur-bearing molecules CnS are comparable to the cyanopolyyne peak of TMC-1. Our results suggest that L1521E would be in a very early stage of physical and chemical evolution.