Abstract
Context.γ
2
Velorum is the closest and visually brightest Wolf-Rayet (WR) binary system. Its eccentric orbit modulates the X-rays observed from the wind-wind interaction, and its large separation enables spatial resolution of both components.
Aims.
We aim to strengthen the constraints on the properties of
γ
2
Velorum and, in particular, to resolve the discrepancy between the eccentricity determined from the emission lines and that from the absorption lines.
Methods.
We obtained VLT/GRAVITY observations and combined them with earlier spatially resolved data covering different orbital phases.
Results.
We determine strong constraints on all orbital parameters and find that
e
= 0.322, close to the value derived from the emission lines. The X-ray light curve declines as
s
−3
after periastron, where
s
is the separation of the two stars, but its modulation is likely affected by absorption and occultation of the X-ray emitting region at other orbital phases. We find that previous discrepancies in the reddening value can be traced to a brighter
K
-band magnitude than predicted by the WR wind models. We derive
E
(
B
−
V
) = 0.02 ± 0.02 mag. Our more precise mass and radius values, combined with previously determined effective temperatures, provide strong constraints on evolutionary models. The closest match for the O star comes from a rotationally mixed model with initial mass
M
init
= 28.7 M
⊙
and an
M
init
= 32 M
⊙
model for the WR star, with negligible accretion onto the O star during the WR progenitor’s Roche lobe overflow phase. However, the temperature of the O star is higher and the mass of the WR star is smaller than predicted by the evolutionary tracks at the current epoch, consistent with the well-known “mass-discrepancy problem” in massive stars.
Conclusions.γ
2
Velorum’s strongly constrained parameters make it ideal for testing structure, evolution, and stellar wind models.