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

Abstract

With the ever faster cadence of untargeted surveys of the sky, the supernova (SN) community will capture in the coming years a growing number of shock breakouts in red-supergiant (RSG) stars. Expecting a high frequency of breakouts within circumstellar material (CSM), we have produced an extended, regular and cubic grid of models covering from low- to high-energy explosions, compact to extended CSM, moderate- to high-density CSM. Here, we document the main results from the radiation-hydrodynamics and nonlocal thermodynamic equilibrium radiative-transfer calculations over the first 15d of evolution, including the bolometric and multi-band 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 OVI3820A) 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 HeII4686A or CIV5805A. This treasury of models will be used to analyze as well as predict future observations of RSG shock breakouts in CSM.

Figures (11)

• Figure 1: Pre-shock breakout density profiles used as initial conditions for the radiation hydrodynamics calculations. The model is for a progenitor star of 15 $M_{\odot}$ initially and evolved at solar metallicity, which after explosion yielded an ejecta with a kinetic energy of $1.2 \times 10^{51}$ erg. The CSM configurations are characterized by a different extent ($R_{\rm CSM}$ values of 2, 6, and $10 \times 10^{14}$ cm) and density ($\dot{\rm M}$ values of 0.1, 0.01, and 0.001 $M_{\odot}$ yr$^{-1}$). (For details, see Section \ref{['sect_setup']}.)
• Figure 2: Illustration of results from the radiation-hydrodynamics calculations for our sample of 27 ejecta/CSM configurations. Left: Peak luminosity versus rise time to peak. Middle: Time-integrated bolometric luminosity versus maximum ejecta velocity, both evaluated at 15 d. Right: CDS velocity versus CDS mass at 15 d. Colors differentiate different model kinetic energies, symbols the mass-loss rate, and the filling style the CSM extent. These indications, which apply to all panels, are given separately, one panel at a time for better visibility. For comparison, we also show the results for the three No-CSM cases (empty diamonds). The interaction phase is not over in models with large CSM mass and extent so the values are not yet converged at 15 d in those cases.
• Figure 3: Bolometric light curves calculated with the multi-group radiation-hydrodynamics code HERACLES and tiled according to the model ejecta kinetic energy (one value per row), CSM density (one value of $\dot{\rm M}$ per column), and CSM extent (three values per panel, with the no-CSM counterpart shown as a dotted line). The x-axis origin is chosen to be when each model first brightens to a luminosity of 10$^{40}$ erg s$^{-1}$, as recorded at the outer grid boundary.
• Figure 4: Comparison between the HERACLES and CMFGEN bolometric light curves for model ekin1p2_mdot0p01_rcsm6e14. The HERACLES light curve has been shifted in time to correct for the light-travel time to the outer grid boundary.
• Figure 5: Same as Fig. \ref{['fig_lbol_heracles']} but now showing the $UVW2$-band light curves computed with CMFGEN for our model set.