  Gravity darkening (GD) and flattening are important consequences of stellar
rotation. The precise characterization of these effects across the HRD is
crucial to a deeper understanding of stellar structure and evolution. We seek
to characterize such important effects on Sargas, an evolved, fast-rotating,
intermediate-mass star, located in a region of the HRD where they have never
been directly measured as far as we know. We use our numerical model CHARRON to
analyze interferometric (VLTI/PIONIER) and spectroscopic (VLT/UVES)
observations through a MCMC model-fitting procedure. The visibilities and
closure phases from the PIONIER data are particularly sensitive to rotational
flattening and GD. Adopting the Roche approximation, we investigate two GD
models: (1) the beta-model (classical von Zeipel's law), and (2) the
omega-model. Using this approach we measure several physical parameters of
Sargas, namely, equatorial radius, mass, equatorial rotation velocity, mean
Teff, inclination and position angle of the rotation axis, and beta. In
particular, we show that the measured beta leads to a surface flux distribution
equivalent to the one given by the omega-model. Thanks to our results, we also
show that Sargas is most probably located in a rare and interesting region of
the H-R diagram: within the Hertzsprung gap and over the hot edge of the
instability strip. These results show once more the power of optical/IR
long-baseline interferometry, combined with high-resolution spectroscopy, to
directly measure fast-rotation effects and stellar parameters, in particular
GD. As was the case for a few fast rotators previously studied by
interferometry, the omega-model provides a physically more profound description
of Sargas' GD, without the need of a beta exponent.
