Protostars and Planets VI, Heidelberg, July 15-20, 2013
Formation of IR emission in HII regions around young stars
Pavlyuchenkov, Yaroslav (Institute of Astronomy of the Russian Academy of Sciences)
Kirsanova, Maria (Institute of Astronomy of the Russian Academy of Sciences)
Akimkin, Vitaly (Institute of Astronomy of the Russian Academy of Sciences)
Wiebe, Dmitry (Institute of Astronomy of the Russian Academy of Sciences)
We investigate the formation of IR emission and corresponding intensity distributions at 8, 24, and 100 micron in HII regions around young massive stars. The evolution of an HII region is simulated using an advanced chemo-dynamical model. Three dust components are included in the model: large silicate grains, very small graphite grains (VSG), and polycyclic aromatic hydrocarbon (PAH) particles. The emergent SED and intensity distributions are calculated using our RT model where stochastic heating of VSG and PAHs is taken into account. The efficiency of two processes for stochastic heating of VSG and PAHs is studied: the absorption of star emission and interaction with hot gas. We compare the synthetic maps with the observed maps from Spitzer and Herschel for the RCW 120 HII region. It is shown that the model with constant PAH abundance cannot reproduce the ring-like appearance of the observed intensity distribution at 8 micron. In order to explain the observed IR distributions we inspect two models of dust evolution. The first model assumes that PAHs are destroyed inside an HII region. In the second model the drift of the dust particles caused by radiation pressure is taken into account. We show that the model with PAH destruction is consistent with observed profiles given appropriate choice of the PAH destruction time. On the contrary, the model with the dust drift is not consistent with observations.
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