Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores

Abstract

We investigate molecular evolution in a star-forming core that is initially a hydrostatic starless core and collapses to form a low-massprotostar. The results of a one-dimensional radiation-hydrodynamicscalculation are adopted as a physical model of the core. We first deriveradii at which CO and large organic species sublimate. CO sublimation inthe central region starts shortly before the formation of the firsthydrostatic core. When the protostar is born, the CO sublimation radiusextends to 100 AU, and the region inside ~100 K. We find thatlarge organic species are formed mainly via grain-surface reactions attemperatures of 20-40 K and then desorbed into the gas phase at theirsublimation temperatures. Carbon-chain species can be formed by acombination of gas-phase reactions and grain-surface reactions followingthe sublimation of CH4. Our model also predicts thatCO2 is more abundant in isolated cores, while gas-phase largeorganic species are more abundant in cores embedded in ambient clouds.