  [Full abstract in the paper] In recent years, protoplanetary disks with
spiral structures have been detected in scattered light, millimeter continuum,
and CO gas emission. The mechanisms causing these structures are still under
debate. A popular scenario to drive the spiral arms is the one of a planet
perturbing the material in the disk. However, if the disk is massive,
gravitational instability is usually the favored explanation. Multiwavelength
studies could be helpful to distinguish between the two scenarios. So far, only
a handful of disks with spiral arms have been observed in both scattered light
and millimeter continuum. We aim to perform an in-depth characterization of the
protoplanetary disk morphology around WaOph 6 analyzing data obtained at
different wavelengths, as well as to investigate the origin of the spiral
features in the disk. We present the first near-infrared polarimetric
observations of WaOph 6 obtained with SPHERE at the VLT and compare them to
archival millimeter continuum ALMA observations. We traced the spiral features
in both data sets and estimated the respective pitch angles. We discuss the
different scenarios that can give rise to the spiral arms in WaOph 6. We tested
the planetary perturber hypothesis by performing hydrodynamical and radiative
transfer simulations to compare them with scattered light and millimeter
continuum observations.
