Dickins, JEIrvine, William M.Snell, Ronald L.Bergin, EASchloerb, FPPratap, PMiralles, MP2024-04-262024-04-262000-0110.1086/317040https://hdl.handle.net/20.500.14394/3289<p>The published version is located at <a href="http://iopscience.iop.org/0004-637X/542/2/870">http://iopscience.iop.org/0004-637X/542/2/870</a></p>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 NH3(1, 1) and (2, 2) rotation-inversion 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 HC3N, N2H+, and CS. The average density toward all lines of sight was 2 × 104 cm-3. As found by previous studies, the emission from various molecular species peaks in different positions: SO and SO2 peak west of the central position, which is the location of the strongest emission from (e.g.) N2H+ and CH3OH, with a second peak occurring for NH3 and HC3N to the north of the center. The most striking abundance variations occur in a north-south cut through the core center for HC3N, C2H, CS, SO, and SO2. A north to south decrease in the abundance of HC3N and CS and a dramatic change in the 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" of the N position, the CS/SO ratio suggests that it is still as "old" as or older than the most evolved region in TMC-1 (the northwest end of the ridge).ISM : abundancesISM : individual (L134N)ISM : moleculesAstrophysics and Astronomyarticle