A modeling perspective on the diversity of red supergiant stars exploding within circumstellar material

¹ Institut d’Astrophysique de Paris, CNRS-Sorbonne Université, 98 bis boulevard Arago, 75014 Paris, France
² Cahill Center for Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 20 October 2025
Accepted: 9 February 2026

Abstract

With the ever faster cadence of untargeted surveys of the sky, the supernova (SN) community will capture a growing number of shock breakouts in red supergiant (RSG) stars in the coming years. Expecting a high frequency of breakouts within circumstellar material (CSM), we have produced an extended regular and cubic grid of models covering low- to high-energy explosions, compact to extended CSM, and moderate- to high-density CSM. We document the main results from the radiation-hydrodynamics and nonlocal thermodynamic equilibrium radiative-transfer calculations over the first 15 d of evolution, including the bolometric and multiband light curves and the salient features from spectra. As before, CSM interaction is found to boost the UV brightness and shorten the optical rise time if compact. Higher ionization (e.g., as seen with O VI 3820 Å) is obtained for more compact CSM, and is maximum for explosions in a vacuum. CSM interaction also diversifies the spectral evolution as seen in line profile morphology, with electron-scattering broadening dominating during the IIn phase. In the absence of CSM, Doppler broadening dominates immediately after shock breakout and leads to strongly blueshifted emission in lines such as He II 4685.70 Å or C IV 5804.86 Å. This treasury of models will be used to analyze and predict future observations of RSG shock breakouts in CSM.