2017ApJS..228...12T

We observed 13 Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N₂H⁺ distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC₃N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N₂H⁺ emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, HN¹³C, N₂D⁺, and cyclic-C₃H₂ toward nine clumps. The detection rate of N₂D⁺ is 50%. Furthermore, we observed the NH₃ emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most targets are cold (<=20 K). In two of the starless clumps we observed, the CCS emission is distributed as it surrounds the N₂H⁺ core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing collapse. In addition, we detected both DNC and N₂D⁺. These two clumps are most likely on the verge of star formation. We introduce the chemical evolution factor (CEF) for starless cores to describe the chemical evolutionary stage, and analyze the observed Planck cold clumps.