On the evolutionary stage of the interacting binary AU Mon

TL;DR

This study investigates the evolutionary stage of the interacting binary AU Mon, using model fitting to determine its current phase and mass transfer characteristics, suggesting recent non-conservative mass transfer activity.

Contribution

It applies a multi-parametric Chi2 minimization with evolutionary models to determine AU Mon's current stage and proposes recent non-conservative mass transfer as an explanation for observed features.

Findings

AU Mon started with initial masses of 4 and 3.6 solar masses.

The system is currently undergoing a Case-B mass-exchange episode.

Recent non-conservative mass transfer explains the lack of orbital period change.

Abstract

We present a study of the evolutionary stage of the interacting binary and Double Periodic Variable AU Monocerotis. A multi-parametric Chi2 minimization is made between the observed parameters and those predicted by the grid of non-conservative and conservative evolutionary models by Van Rensbergen et al., finding the model that best represents the current stellar and system parameters. According to this model, the system started with initial masses 4 M_sun and 3.6 M_sun and orbital period 3.0 days, 196 million years ago, and at present undergoes a Case-B mass-exchange episode. This evolutionary stage is consistent with the reported existence of a circumprimary accretion disk. However, the implied high mass transfer rate contrasts with the absence of significant orbital period change if the mass exchange is conservative. We show that this can occur if the system has recently entered in a non-conservative stage of mass transfer and the efficiency of mass and angular momentum loss satisfy certain conditions.