We present a progress report on HCN(1-0) line observations toward starless cores to probe inward motions. We have made a single pointing survey toward the central regions of 85 starless cores and performed mapping observations of 6 infall candidate starless cores. The distributions of the velocity difference between HCN(1-0) hyperfine lines and the optically thin tracer N2H+(1-0) are significantly skewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to the blue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence than CS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infall asymmetry seen in HCN(1-0) hyperfine lines, CS(3-2), CS(2-1), DCO+(2-1) and N2H+ observations. The HCN(1-0) F(O-l) with the least optical depth usually shows a similar intensity distribution to that of N2H+ which closely traces the density distribution of the cores, indicating that HCN(1-0) is less chemically affected and so believed to reflect kinematics occurring in rather inner regions of the cores. Detailed radiative transfer model fits of the spectra are underway to analyze central infall kinematics in starless cores.

• J. SOHN(Astronomy Program, SEES, Seoul National University/Korea Astronomy Observatory)
• C. W. LEE(Korea Astronomy Observatory)
• H, M. LEE(Astronomy Program, SEES, Seoul National University)
• Y.-S. PARK(Astronomy Program, SEES, Seoul National University)
• P. C. MYERS(Harvard-Smithsonian Center for Astrophysics)
• Y. LEE(Korea Astronomy Observatory)
• M. TAFALLA(Observatorio Astronomico Nacional)