We present the first comprehensive study on 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 , C _ { 3 } S , C _ { 4 } H , HC _ { 3 } N , and HC _ { 5 } N. On the other hand , the NH _ { 3 } lines are weak and the N _ { 2 } H ^ { + } lines are not detected .
According to our mapping observations of the HC _ { 3 } N , CCS , and C _ { 3 } S lines , the dense cores in L1495B and L1521B are compact with the radius of 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 H ^ { 13 } CO ^ { + } , HN ^ { 13 } C , and C ^ { 34 } S lines are detected in L1495B and L1521B , the densities of these cores are high enough to excite the NH _ { 3 } and N _ { 2 } H ^ { + } lines .
Therefore , the abundances of NH _ { 3 } and N _ { 2 } H ^ { + } relative to carbon-chain molecules are apparently deficient , as observed in L1521E .
We found that longer carbon-chain molecules such as HC _ { 5 } N and C _ { 4 } H are more abundant in TMC-1 than L1495B and L1521B , while those of sulfur-bearing molecules such as C ^ { 34 } S , CCS , and C _ { 3 } S are comparable .
Both distributions and abundances of the observed molecules of L1495B and L1521B are quite similar to those of L1521E , strongly suggesting that L1495B and L1521B is in a very early stage of physical and chemical evolution .