Molecular Chemistry in Gaseous Disks Around Young Hot Stars

Abstract

We investigate the formation of molecules and especially CO and H₂O in the inner hot and dense part of disks around young high mass stars using a timedependent gas-phase chemical model. CO molecules are chemically destroyed above 3000 K, much lower than the vibrational dissociation temperature of 5000 K. CO is photo-dissociated at high rates but this destruction is compensated by the high formation rate. Water molecules are sufficiently abundant to be detectable. The simulations support the presence of CO and H₂O molecules in inner disks around young massive stars. The chemistry in hot (T > 1000 K) moderately dense (n_H = 10⁶–10⁹ cm^–3) quiescent environments is in many aspects similar to that in post-shock regions although significant differences exist like stronger photo-reactions and three-body reactions.