Thermonuclear explosions as Type II supernovae^⋆

¹ Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
e-mail: sasha.kozyreva@gmail.com
² Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Philosophenweg 12, 69120 Heidelberg, Germany
³ M.V. Lomonosov Moscow State University, Sternberg Astronomical Institute, 119234 Moscow, Russia

Received: 15 October 2023
Accepted: 16 January 2024

Abstract

We consider a binary stellar system in which a low-mass (0.6 M_⊙) carbon-oxygen white dwarf (WD) merges with the degenerate helium core (0.4 M_⊙) of a red giant. We analyse the outcome of a merger within a common envelope (CE). We predict the observational properties of the resulting transient. We find that the double detonation of the WD, being a pure thermonuclear explosion and embedded into the hydrogen-rich CE, has a light curve with the distinct plateau shape of a supernova (SN) Type IIP, with a duration of about 40 days. We find five observed SNe IIP (SN 2004dy, SN 2005af, SN 2005hd, SN 2007aa, and SN 2008bu) that match the V-band light curve of our models. Hence, we show that a thermonuclear explosion within a CE might be mistakenly identified as a SN IIP, believed to be an outcome of a core-collapse neutrino-driven explosion of a massive star. We discuss a number of diagnostics that may help to distinguish this kind of thermonuclear explosion from a core-collapse SN.