SIMBAD references

We present the first comprehensive study of physical and chemical properties of quiescent starless cores L1495B and L1521B, which are known to be rich in carbon-chain molecules like the cyanopolyyne peak of TMC-1 and L1521E. We have detected radio spectral lines of various carbon-chain molecules, such as CCS, C₃S, C₄H, HC₃N, and HC₅N. On the other hand, the NH₃ lines are weak and the N₂H⁺ lines are not detected. According to our mapping observations of the HC₃N, CCS, and C₃S lines, the dense cores in L1495B and L1521B are compact, with radius 0.063 and 0.044 pc, respectively, and have a simple elliptical structure. The distributions of 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. Since the H¹³CO⁺, HN¹³C, and C³⁴S lines are detected in L1495B and L1521B, the densities of these cores are high enough to excite the NH₃and N₂H⁺ lines. Therefore, the abundances of NH₃and N₂H⁺ relative to carbon-chain molecules are apparently deficient, as observed in L1521E. We found that longer carbon-chain molecules, such as HC₅N and C₄H, are more abundant in TMC-1 than in L1495B and L1521B, while those of sulfur-bearing molecules, such as C³⁴S, CCS, and C₃S, are comparable. Both distributions and abundances of the observed molecules in L1495B and L1521B are quite similar to those in L1521E, strongly suggesting that L1495B and L1521B are in a very early stage of physical and chemical evolution.