CH₃CN J = 8 − 7 and CS J = 3 − 2 emission in orion KL

Abstract

The data of the line series CH₃CN 8(K) − 7(K) K = 0 − 7 and line CS J = 3 − 2 were taken simultaneously. At beam size of 16″ the emissions of CH₃CN and CS have a common center position located near IRc2 with deviations Δα ∼ -8″ and Δδ ∼ 5″. The observed data show that in Orion KL core the integrated intensities of the two species have double peaks separated by a space of 14″. The 2-dimension Gaussian fitting plots (FWHM) are ellipses ofD _maj = 26″ andD _min = 22″ for CH₃CN 8(K) − 7(K) K = 3 − 6 andD′_maj = 39″ D′_min = 31″ for CS J = 3 − 2 at a distance about 450 pc. Towards the multiple line emission region of CH₃CN 8(K) − 7(K) K = 3 − 6, using a simplified very large velocity gradient model to solve the statistical equilibrium and radiative transfer equations, we find to fit the observed results, the optimum physical parameters and kinetic temperatureT _k∼ 120 K, densityn(H _a) ∼ 1.2 × 10⁵ cm⁻³, velocity gradientV _gr∼ 92 km s⁻¹ pc⁻¹ and the local abundance of CH₃CNF _ab∼ 3 × 10⁻⁸. However towards the region of single line emission of CS J = 3 − 2 we have to use LTE and the optical thin approximation on the assumption ofT _k= 120 K to obtain the lower limits of column density and then, an averaged abundance of CS of 6 × 10⁻⁸.