  We report on interferometric AMBER/VLTI observations of the recurrent nova RS
Oph five days after its outburst on 2006 Feb 12. Using three baselines from 44
to 86m, and a spectral resolution of 1500, we measured the extension of the
emission in the K band continuum and in the BrG and HeI2.06 micron lines. The
continuum visibilities were interpreted by fitting simple geometric models
consisting of uniform and Gaussian ellipses, ring and binary models. The
visibilities and differential phases in the BrG line were interpreted using
skewed ring models aiming to perform a limited parametric reconstruction of the
extension and kinematics of the line forming region. The limited uv coverage
does not allow discrimination between filled models and rings. Binary models
are discarded because the measured closure phase in the continuum is close to
zero. The visibilities in the lines are at a low level compared to their nearby
continuum, consistent with a more extended line forming region for HeI2.06 than
BrG. The ellipse models for the continuum and for the lines are highly
flattened and share the same position angle. Two radial velocity fields are
apparent in the BrG line: a 'slow' expanding ring-like structure (v~1800km/s),
and a 'fast' structure extended in the E-W direction (v~2500-3000km/s). These
results confirm the basic fireball model, contrary to the conclusions of other
interferometric observations conducted by Monnier et al. (2006).
