Properties of the Molecular Cores of Low Luminosity Objects
  We present a survey toward 16 Low Luminosity Objects (LLOs with an internal
luminosity, Lint, lower than 0.2 Lsun) with N2H+ (1-0), N2H+ (3-2), N2D+ (3-2),
HCO+ (3-2) and HCN (3-2) using the Arizona Radio Observatory Kitt Peak 12m
Telescope and Submillimeter Telescope. Our goal is to probe the nature of these
faint protostars which are believed to be either very low mass or extremely
young protostars. We find that the N2D+/N2H+ column density ratios of LLOs are
similar to those of typical starless cores and Class 0 objects. The N2D+/N2H+
column density ratios are relatively high (> 0.05) for LLOs with kinetic
temperatures less than 10 K in our sample. The distribution of N2H+ (1-0) line
widths spreads between that of starless cores and young Class 0 objects. If we
use the line width as a dynamic evolutionary indicator, LLOs are likely young
Class 0 protostellar sources. We further use the optically thick tracers, HCO+
(3-2) and HCN (3-2), to probe the infall signatures of our targets. We derive
the asymmetry parameters from both lines and estimate the infall velocities by
fitting the HCO+ (3-2) spectra with two-layer models. As a result, we identify
eight infall candidates based on the infall velocities and seven candidates
have infall signatures supported by asymmetry parameters from at least one of
HCO+ (3-2) and HCN (3-2).
