1999ApJ...518L..37W

We present combined single-dish and interferometric CS (2-1) and N₂H⁺ (1-0) observations of a compact core in the northwest region of the Serpens molecular cloud. The core is starless according to observations from optical to millimeter wavelengths, but its lines have turbulent widths and ``infall asymmetry.'' Line profile modeling indicates supersonic inward motions v_in≳0.34 km.s^–1 over an extended region L>12,000 AU. The high infall speed and large extent exceeds the predictions of most thermal ambipolar diffusion models and points to a more dynamical process for core formation. A short (dynamic) timescale, ∼10⁵ yr≃L/v_in, is also suggested by the low N₂H⁺ abundance, ∼1x10^–10.