Evaporation of Grain-Surface Species by Shock Waves in a Protoplanetary Disk

Recent Atacama Large Millimeter/submillimeter Array observations of young protostellar objects detected warm SO emission, which could be associated with a forming protostellar disk. In order to investigate if such warm gas can be produced by accretion shock onto the forming disk, we calculate the sputtering and thermal desorption of various grain-surface species in one-dimensional shock waves. We find that thermal desorption is much more efficient than the sputtering in the post-shock region. While H 2 O can be thermally desorbed, if the accretion velocity is larger than 8 km s −1 with the pre-shock gas number density of 10 9 cm −3 , SO is desorbed if the accretion velocity ≳2 km s −1 and ≳4 km s −1 , with the pre-shock density of 10 9 cm −3 and 10 8 cm −3 , respectively. We also find that the column density of hydrogen nuclei in warm post-shock gas is N warm ∼ 10 21 cm −2 .