Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

Abstract

Abstract We have observed molecular cloud cores in the Orion A giant molecular cloud (GMC) in CCS, HC$_3$N, DNC, and HN$^{13}$C to study their chemical characteristics. We detected CCS in the Orion A GMC for the first time. CCS was detected in about a third of the observed cores. The cores detected in CCS are not localized, but widely distributed over the Orion A GMC. The CCS peak intensity of the core tends to be high in the southern region of the Orion A GMC. The HC$_3$N peak intensity of the core also tends to be high in the southern region, while there are HC$_3$N intense cores near Orion KL, which is not seen in CCS. The core associated with Orion KL shows a broad HC$_3$N line profile, and the star-formation activity near to Orion KL seems to enhance the HC$_3$N emission. The column density ratio of NH$_3$ to CCS is lower near the middle of the filament, and higher toward the northern and southern regions along the Orion A GMC filament. This ratio is known to trace the chemical evolution in nearby dark cloud cores, but seems to be affected by the core gas temperature in the Orion A GMC: cores with low NH$_3$ to CCS column density ratios tend to have a warmer gas temperature. The value of the column density ratio of DNC to HN$^{13}$C is generally similar to that in dark cloud cores, but becomes lower around Orion KL due to a higher gas temperature.