We present a picture of star formation around the H ii region Sh2‐235 (S235) based upon data on the spatial distribution of young stellar clusters and the distribution and kinematics of molecular gas around S235. We observed 13CO (1–0) and CS (2–1) emission toward S235 with the Onsala Space Observatory 20‐m telescope and analysed the star density distribution with archival data from the Two Micron All‐Sky Survey (2MASS). Dense molecular gas forms a shell‐like structure at the southeastern part of S235. The young clusters found with 2MASS data are embedded in this shell. The positional relationship of the clusters, the molecular shell and the H ii region indicates that expansion of S235 is responsible for the formation of the clusters. The gas distribution in the S235 molecular complex is clumpy, which hampers interpretation exclusively on the basis of the morphology of the star‐forming region. We use data on kinematics of molecular gas to support the hypothesis of induced star formation, and distinguish three basic types of molecular gas components. The first type is primordial undisturbed gas of the giant molecular cloud, the second type is gas entrained in motion by expansion of the H ii region (this is where the embedded clusters were formed) and the third type is a fast‐moving gas, which might have been accelerated by winds from the newly formed clusters. The clumpy distribution of molecular gas and its kinematics around the H ii region implies that the picture of triggered star formation around S235 can be a mixture of at least two possibilities: the ‘collect‐and‐collapse’ scenario and the compression of pre‐existing dense clumps by the shock wave.

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The generation of infrared (IR) radiation and the observed IR intensity distribution at wavelengths of 8, 24, and 100 µm in the ionized hydrogen region around a young, massive star is investigated. The evolution of the HII region is treated

We consider dust drift under the influence of stellar radiation pressure during the pressure-driven expansion of an H ii region using the chemo-dynamical model MAR-ION. Dust size distribution is represented by four dust types: conventional polycyclic aromatic hydrocarbons (PAHs), very small grains (VSGs), big grains (BGs) and also intermediate-sized grains (ISGs), which are larger than VSGs and smaller than BGs. The dust is assumed to move at terminal velocity determined locally from the balance between the radiation pressure and gas drag. As Coulomb drag is an important contribution to the overall gas drag, we evaluate a grain charge evolution within the H ii region for each dust type. BGs are effectively swept out of the H ii region. The spatial distribution of ISGs within the H ii region has a double peak structure, with a smaller inner peak and a higher outer peak. PAHs and VSGs are mostly coupled to the gas. The mean charge of PAHs is close to zero, so they can become neutral from time to time because of charge fluctuations. These periods of neutrality occur often enough to cause the removal of PAHs from the very interior of the H ii region. For VSGs, the effect of charge fluctuations is less pronounced but still significant. We conclude that accounting for charge dispersion is necessary to describe the dynamics of small grains.