研究成果・発表論文

Effects of Grain Growth on Molecular Abundances in Young Stellar Objects

Harada, Nanase,   Hasegawa, Yasuhiro,   Aikawa, Yuri,   Hirashita, Hiroyuki,   Liu, Haoyu Baobab,   & Hirano, Naomi


要旨
Recent observations suggested that the growth of dust grains may have already occurred in class 0/I young stellar objects (YSOs). Since chemical reactions on dust grain surfaces are important in determining molecular abundances, the dust size growth may affect chemical compositions in YSOs significantly. In this work, we aim to determine how grain growth affects chemical abundances. We use a time-dependent gas-grain chemical model for a star-forming core to calculate the gas-phase and grain-surface chemical abundances with variation of surface areas of grains to imitate grain growth. We also perform parameter studies in which the initial molecular abundances vary. Our results show that a smaller extent of the surface areas caused by grain growth changes the dominant form of sulfur-bearing molecules by decreasing H$_2$S abundances and increasing SO and/or SO$_2$ abundances. We also find that complex organic molecules such as CH$_3$CN decrease in abundances with larger grain sizes, while the abundance of other species such as CH$_3$OCH$_3$ is dependent on other parameters such as the initial conditions. Comparisons with observations of a class 0 protostar, IRAS 16293-2422, indicate that the observed abundance ratios between sulfur-bearing molecules H$_2$S, SO, and SO$_2$ can be reproduced very well when dust grains grow to a maximum grain size of a $_max$ = 10-100 \ensuremathμm.




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