Confined Circumstellar Material as a Dust Formation Site in Type II Supernovae

We propose a model for dust formation in Type II supernovae (SNe) interacting with confined circumstellar material (CSM), motivated by recent time-domain surveys that have revealed a substantial fraction of SN progenitors to be surrounded by CSM ejected shortly before core-collapse. We simulate the pre-SN mass eruption and the resulting confined CSM using the open-source code CHIPS, and follow the subsequent evolution of the SN ejecta and its interaction with the CSM. We show that a cold dense shell (CDS) is formed at the radiative shock under a wide range of conditions and later undergoes rapid adiabatic cooling during free expansion, leading to efficient dust condensation. The resulting dust mass ranges from $\sim10^{-3}\,M_\odot$ to $0.1\,M_\odot$, depending on the mass and spatial extent of the CSM. We further calculate the infrared (IR) emission from the newly formed dust and find broad consistency with observations of SN~1998S. Notably, the IR light curve exhibits a rapid rise within $\lesssim10\,{\rm d}$, closely resembling that of kilonovae (KNe). This suggests that dust emission powered by confined CSM interaction may be also discovered in KN searches. Moreover, the high-density environment of the CDS may allow dust grains to grow to larger sizes, enhancing their survivability against destruction by reverse shocks propagating from the interstellar medium at later times.