You-Ting Yeh , Sheng-Jun Lin , Shih-Ping Lai ,Nakamura Fumitaka
We want to estimate the evolutionary status of molecular cores in Orion A by calculating the abundance ratio of N2D+ and N2H+. Previous studies show that [D]/[H] ratio increases in prestellar cores when CO depletion becomes significant and decrease rapidly after the protostars form due to stellar radiation (Crapsi et al. 2005). The region we choose is Orion A which contains many cores in different environment, providing constrain on the chemical evolutionary models. We have obtained N2D+(1-0) and N2H+(1-0) spectrum with Nobeyama 45m toward 27 cores in Orion A. Our results will display the evolutionary status of these cores across the whole Orion A cloud.