Supernovae from massive stars with extended tenuous envelopes

TL;DR

This paper investigates how extended, tenuous envelopes in massive stars influence supernova explosions, affecting light curves, spectra, and ejecta properties, with implications for understanding various observed supernova types.

Contribution

It introduces detailed simulations of supernovae from stars with extended envelopes, revealing new insights into their light curves, spectra, and ejecta dynamics.

Findings

Extended envelopes cause shock braking and reverse shock formation.

Light curves exhibit a double-peak morphology due to delayed 56Ni heating.

Ejecta properties explain narrower line profiles in some supernovae types.

Abstract

Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e., stars in which 95% of the mass is contained within 10% of the surface radius or less). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5Msun. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Halpha profile seen in SN1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue color, and featureless spectra reminiscent of the Type Ib SN2008D, suggesting a low-mass progenitor.