Speckle imaging of γ2 Velorum: the inner wind possibly resolved

Abstract

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-infrared spectroscopy suggested that the wind of the nearest Wolf–Rayet (WR) star, γ2 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 γ2 Vel at two orbital phases (0.30 and 0.44) with two narrow-band and two intermediate-band filters in an attempt to resolve its wind. Our observations demonstrate that γ2 Vel’s wind 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.