2007ApJ...660.1326L

In an attempt to understand the dynamics of collapsing starless cores, we have conducted a detailed investigation of the velocity fields of two collapsing cores, L694-2 and L1197, with high spatial resolution HCN J=1-0 maps and Monte Carlo radiative transfer calculation. It is found that infall motion is most active in the middle and outer layers outside the central flat region of the density profile, while both the central and outermost parts of the cores are static or exhibit slower motion. The objects' peak velocities are 0.28 km/s for L694-2 and 0.20 km/s for L1197, which could not be found in simple models. These velocity fields are roughly consistent with the gravitational collapse models of the isothermal core; however, the velocity gradients inside the peak velocity position are steeper than those of the models. Our results also show that the density distributions are ∼r^–2.5 and ∼r^–1.5 in the outer part for L694-2 and L1197, respectively. HCN abundance relative to H₂ is spatially almost constant in L694-2, with a value of 7x10^–9, while for L1197 it shows a slight inward increase from 1.7 to 3.5x10^–9.