Modeling Occurrences of Type 1a Supernovae and other End States of Common Envelope Evolution from a Third Star on a White Dwarf Inner Binary
Creators: name: Khwaja, Amaan
Publisher: name: Zenodo
Year: 2024
Subjects: triple star system
supernovae
star evolution
supernovae predictions
Astro 98

description: Hierarchical triple systems pose interesting questions in astrophysics, as the effect of the outer star could have a profound impact on the evolution of the inner binary and its potential to merge. A particularly intriguing case of triple systems are those with a double white dwarf inner binary system with a third outer companion. In this paper, we explore the effects of such a third star on the occurrences of double degenerate supernovae (WD-WD mergers) as compared to the standard WD- WD binary scenario. Specifically examining the cases where the third star is a giant overflowing its Roche lobe, causing its envelope to engulf the system of three stars, leading to an inward spiral of the orbits. Understanding the effects of the common envelope phase in triples is important, as it allows us to gain insight into how the consideration of a third star may affect our predictions for the occurrences of supernovae in WD-WD binaries. To compute the effect of the common envelope on orbital separations, we employ the SCATTER (Single Components’ Angular momenTum TransfER) formalism from Di Stefano et al. (2023), which uses angular momentum transfer to arrive at the final states of the system without needing to rely on complex hydrodynamical simulations or any of the underlying physics behind Common Envelopes. Instead by assuming circular orbits and using angular momentum conservation, whilst assuming angular momentum is transferred directly from stars to the envelope, SCATTER can solve for final orbital separations of Common Envelope evolution. For the purposes of our model, we consider our inner binary to be composed of 2 white dwarf stars with a red giant companion. We then run calculations to solve for the final orbital state of the system and determine whether it will merge within a Hubble time and what that merger will look like: a Type Ia supernova, an AIC (collapse into a neutron star), or a merger of low-mass white dwarfs. We find that for simulations of WD-WD binaries with an outer red giant star in the range of 0.8–6MJ, common envelope evolution results in over twice the amount of supernova events, with roughly 2.5 times the overall frequency for mergers of the inner binary. Our results show that common envelope evolution could have a profound effect not only on the orbit of the inner binary but also on the outer binary, where, although all our systems are initially stable, we find roughly 4% will lose stability within a Hubble time after common envelope evolution, and another 0.5% will experience a second merger with the third star. With our results, we can then get an idea of how the consideration of a third star outside of a WD-WD binary could affect the occurrences of double-degenerate supernovae. Thus, our results help provide us with a better understanding of the evolution of triple systems and how such systems differ from the standard binary case. Such considerations are important as triple systems make up a substantial portion of known stellar systems (10% of F and G stars are home to triples (Toonen, S. et al. 2020)). Our paper therefore helps establish the need for further investigation into triples as progenitors for type 1a supernovae.
description: Astro 98