Numerical simulations and infrared spectro-interferometry reveal the wind collision region in gamma2 Velorum

TL;DR

This study combines infrared interferometry and hydrodynamic simulations to identify and analyze the wind collision region in the gamma2 Velorum binary system, revealing its structure and contribution to infrared emission.

Contribution

It provides the first detailed spatial and spectral analysis of the wind collision zone in gamma2 Velorum using multi-epoch VLTI data and 3D hydrodynamic modeling.

Findings

The wind collision region contributes 3-10% of near-infrared flux.

The system's binary parameters and distance are confirmed.

The hydrodynamic model reveals a 3D spiral structure in the collision zone.

Abstract

Colliding stellar winds in massive binary systems have been studied through their radio, optical lines and strong X-ray emission for decades. More recently, near-infrared spectrointerferometric observations have become available in a few systems, but isolating the contribution from the individual stars and the wind collision region still remains a challenge. In this paper, we study the colliding wind binary gamma2 Velorum and aim at identifying the wind collision zone from infrared interferometric data, which provide unique spatial information to determine the wind properties. Our analysis is based on multi-epoch VLTI/AMBER data that allows us to separate the spectral components of both stars. First, we determine the astrometric solution of the binary and confirm previous distance measurements. We then analyse the spectra of the individual stars, showing that the O star spectrum is peculiar within its class. Then, we perform three-dimensional hydrodynamic simulations of the system from which we extract model images, visibility curves and closure phases which can be directly compared with the observed data. The hydrodynamic simulations reveal the 3D spiral structure of the wind collision region, which results in phase-dependent emission maps. Our model visibility curves and closure phases provide a good match when the wind collision region accounts for 3 to 10 per cent of the total flux in the near infrared. The dialogue between hydrodynamic simulations, radiative transfer models and observations allows us to fully exploit the observations. Similar efforts will be crucial to study circumstellar environments with the new generation of VLTI instruments like GRAVITY and MATISSE.