Speckle Imaging of Gamma2 Velorum: The Inner Wind Possibly Resolved

TL;DR

This study uses high-resolution speckle imaging to potentially resolve the inner wind structure of Gamma2 Vel, providing insights into wind asymmetries and clumping in Wolf-Rayet stars, which are crucial for accurate mass-loss rate estimates.

Contribution

First direct imaging attempt to resolve the inner wind of Gamma2 Vel using speckle imaging, revealing possible asymmetry at unprecedented small scales.

Findings

Possible wind asymmetry resolved at 0.07 arcsec (24 AU) scale.

Detected a westward elongation in the wind structure.

Highlights need for multi-phase imaging to understand wind features.

Abstract

Accurately quantifying the rates dM/dt at which massive stars lose mass is essential to any understanding of their evolution. All dM/dt estimates to date assume wind clumping factors; not allowing for clumping leads to overestimates of dM/dt and underestimates of lifetimes and masses when these stars explode as supernovae. Mid-IR spectroscopy suggested that the wind of the nearest Wolf-Rayet star, Gamma2 Vel, is resolved with a Full Width at 10 per cent intensity of 0.5 arcsec, or 171 AU at the 342 pc distance of the star. As the Zorro speckle imager on Gemini-South is capable of 0.02 arcsec resolution, we have used it to image Gamma2 Vel at two orbital phases (0.30 and 0.44) with two narrowband and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that the wind of Gamma2 Vel may be resolved as a 0.07 arcsec westward elongation through an 832 nm filter at orbital phase 0.3 . If confirmed, this is the smallest scale (24 AU) at which a WR star wind asymmetry has been directly imaged. Similar imaging at multiple phases is needed to determine if the asymmetry is due to stochastic wind clumping, co-rotating interaction regions or colliding-wind, cone-shaped shocks.