A Study of the Physics and Chemistry of L134N

Abstract

We have carried out a comprehensive and self-consistent study of the physical and chemical state of the core of the dark cloud L134N (L183), whose molecular abundances provide a standard against which chemical models may be compared. We used observations of the 1) and (2, 2) rotation-inversion NH3 (1, transitions to estimate the kinetic temperature, which was found to be consistent with 10 K and not varying with position. Densities were determined from multitransition statistical equilibrium calculations for and CS. The average density toward all lines of sight was 2 HC ] 104 cm~3. As found by 3 N, N2 H`, previous studies, the emission from various molecular species peaks in di†erent positions : SO and SO2 peak west of the central position, which is the location of the strongest emission from (e.g.) and N2 H` CH with a second peak occurring for and to the north of the center. The most striking 3 OH, NH3 HC3 N abundance variations occur in a north-south cut through the core center for CS, SO, and HC3 N, C2 H, SO A north to south decrease in the abundance of and CS and a dramatic change in the 2 . HC3 N CS/SO ratio, which has been shown to be a sensitive tracer of chemical evolutionary state, suggests that the north is at a younger evolutionary state than the south. Despite the ““ youth ÏÏ of the N position, the CS/SO ratio suggests that it is still as ““ old ÏÏ as or older than the most evolved region in TMC-1 (the northwest end of the ridge).