  Optical interferometry is a powerful tool to investigate the close
environment of AGB stars. With a spatial resolution of a few milli-arcseconds,
it is even possible to image directly the surface of angularly large objects.
This is of special interest forMira stars and red supergiants for which the
dust-wind is initiated from or very close to the photosphere by an interplay
between pulsation and convection. Based on two-epoch interferometric
observations of the Mira star X Hya, we present how the variation of the
angular size with wavelength challenges pulsation models and how reconstructed
images can reveal the evolution of the object shape and of its asymmetric
structures.
