We have carried out a survey toward the central regions of 85 starless cores in HCN J = 1 - 0 to study inward motions in the cores .
Sixty-four cores were detected with HCN lines .
The infall asymmetry in the HCN spectra is found to be more prevalent , and more prominent than in any other previously used infall tracers such as CS J = 2 - 1 , DCO ^ { + } J = 2 - 1 , and N _ { 2 } H ^ { + } J = 1 - 0 .
We found close relation between the intensities of the HCN and N _ { 2 } H ^ { + } lines .
This implies that the HCN is not much depleted in the central regions of the cores .
In some cores , the HCN spectra show different sign of asymmetry from other molecular lines .
A few cores show various signs of asymmetry in individual HCN hyperfine lines .
The distribution of the velocity shift \delta V of the HCN profiles with respect to the systemic velocity of the optically thin tracer is found to be more shifted toward bluer side than those of other infall tracers , indicating that the HCN traces inward motions more frequently .
The \delta V distribution of each HCN hyperfine line for all sources is similar .
Moreover the \delta V values obtained from different HCN hyperfine lines for each source are nearly similar .
These may mean that most of starless cores are in similar kinematic states across the layers of the cores .
We identify 17 infall candidates using all available indicators such as the velocity shift \delta V and the blue to red peak intensity ratio of double peaked profiles for HCN J = 1 - 0 , CS J = 2 - 1 , J = 3 - 2 , DCO ^ { + } J = 2 - 1 , and N _ { 2 } H ^ { + } J = 1 - 0 .
Four of them , L63 , L492 , L694-2 , and L1197 are found to show higher blue to red ratio in the HCN hyperfine line along the lower opacity , suggesting that infall speed becomes higher toward the center .