Asymmetric radiation in binary systems: Implications for disk evolution and chemistry

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² School of Physics and Astronomy, Monash University, Vic. 3800, Australia
³ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

^★ Corresponding author: pedro.poblete@univ-grenoble-alpes.fr

Received: 18 June 2025
Accepted: 15 September 2025

Abstract

Context. Current models of binary systems often depend on simplified approximations of the radiation field, which are unlikely to accurately capture the complexities of asymmetric environments.

Aims. We investigate the dynamical and chemical implications of a 3D asymmetric radiation field that accounts for the optical properties of sub-structures present in a protoplanetary disk, as well as the inclusion of a secondary radiation source in binary systems.

Methods. We conducted a series of 3D-SPH hydrodynamical simulations using Phantom, coupled with the 3D Monte Carlo radiative transfer code Mcfost, to compute disk temperatures on-the-fly. We explored different binary-disk orientations (0° and 30°) for an eccentric binary, along with a constant dust-to-gas ratio and dust as a mixture prescription. We also simulated an outburst event as an example of a drastic increase in luminosity.

Results. Heating from the secondary star inflates the outer disk, increasing the aspect ratio facing the companion by about 25% in inclined configurations compared to 10% in coplanar ones. Dust settling in the mid-plane enhances extinction along the disk plane, making the coplanar configuration cooler than the inclined one on the side of the disk facing the companion. Additional heating causes a shift in the snow line for species with freeze-out temperatures below 50 K, depending on the disk-binary inclination and binary phase. During outbursts, the aspect ratio doubles on the star-facing side and increases by 50% on the opposite side in inclined cases. The snow line shift would impact all the species considered in the outburst case.

Conclusions. Protoplanetary disk heating in binary systems depends on stellar properties, the binary phase, and disk local and global characteristics. This results in temperature asymmetries, especially during secondary star outbursts, leading to variations in aspect ratio and snow lines that can affect chemistry and planet formation.