Two-Dimensional Radiation-Hydrodynamic Simulations of Luminous Red Novae

TL;DR

This study uses two-dimensional radiation-hydrodynamic simulations to model luminous red novae, revealing complex light curves influenced by circumstellar material and viewing angles, advancing understanding of binary stellar mergers.

Contribution

First detailed 2D simulations of LRNe including recombination and opacities, showing how circumstellar material shapes observable light curves and their diversity.

Findings

Light curves feature a blue peak followed by a red shock-powered plateau.

Luminosities reach up to 10^41 erg/s with durations up to 200 days.

Viewing angle and circumstellar material distribution significantly affect observations.

Abstract

Luminous Red Novae (LRNe) are transients associated with mass ejection during stellar mergers and common envelope evolution (CEE). LRNe have the potential to illuminate the poorly understood phases of binary evolution leading up to the CEE, during the mass ejection phase, and in the immediate aftermath. However, the mechanism responsible for powering LRN light curves and the origin of their observed diversity remain open questions. Here, we perform two-dimensional moving-mesh radiation-hydrodynamic simulations of LRNe that take into account hydrogen and helium recombination and relevant opacities. We study a typical high-mass stellar merger, which dynamically ejects 2 $M_\odot$ with a characteristic velocity of 410 km/s. This ejecta collides with 2.7 $M_\odot$ of equatorially concentrated circumbinary material (CBM) left behind from a prior phase of non-conservative runaway mass transfer. We find that the resulting light curve is composed of a short, blue peak followed by a redder, predominantly shock-powered plateau with luminosities reaching up to $10^{41}$ erg/s and durations up to 200 days. These luminosities are significantly higher, and the durations much longer, than those produced by a simple spherical ejection of the same mass. They also depend in a complex way on the radial distribution of the CBM and the viewing angle. The shock is embedded in the ejecta and its observational signatures during the optically-thick phase are largely hidden. Our results are broadly compatible with observations of the brightest extragalactic LRNe and pave the way for the transformation of LRNe into powerful probes of binary evolution.