Molecular studies of two dark nebulae associated with Herbig-Haro objects

Narrow (not more than 2 km/sec wide) emission lines from millimeter- and centimeter-wave transitions of a number of molecules have been detected toward several dark nebulae known to contain H-H objects and infrared stars that are thought to be very young. Large dense clouds have been mapped in 2-mm H2CO emission toward NGC 1333 and M78. Determinations of nearly constant kinetic temperature through carbon-12 monoxide and NH3 observations in NGC 1333 indicate that the slight peaking of the emission from H2CO, CS, and HCN is probably due to increased gas density near the H-H object/infrared-star associations. Implied gravitational-collapse velocities are much larger than those allowed by the observed narrow molecular line widths.