Efficiency of viscous angular momentum transport in dissipating Be binaries

Abstract

Angular momentum transport is a fundamental process shaping the structure, evolution, and lifespans of stars and disks across a wide range of astrophysical systems. Be stars offer a valuable environment for studying viscous transport of angular momentum in massive stars, thanks to their rapid rotation, observable decretion disks, and likely absence of strong magnetic fields. This study analyzes angular momentum loss in 40 Be binary simulations spanning a range of orbital separations and companion masses, using a smoothed-particle hydrodynamics (SPH) code. A novel framework is introduced to define the outer disk edge based on the behaviour of the azimuthal velocity, streamlining the analysis of angular momentum transport within the system. Applying this framework reveals that systems with smaller truncation radii tend to reaccrete a larger fraction of their angular momentum during dissipation, thereby inhibiting the stars ability to regulate its surface rotation. Modification of this rate may alter the star´s mass-injection duty cycle or long-term evolutionary track. Finally, a subset of the simulations were post-processed using the Monte Carlo radiative transfer code HDUST, generating synthetic observables including Hα line profiles, V-band polarization, and UV polarization. Suggestions for observational verification of the dynamical results are demonstrated using the simulated data.