High Angular Resolution Campaign Reveals A Specific Evolutionary Stage of a Pre-Transitional Disk

HD179218 is a Herbig star surrounded by a pre-transitional disk. Its extremely large apparent size in the near-infrared makes it an outlier in the sample of Herbig stars observed by interferometry. We present the results of an observational campaign on this object, involving different high angular resolution techniques, such as polarimetric direct imaging (SPHERE/ZIMPOL), aperture masking (KECK/NIRC2) and long baseline interferometric instruments (VLTI/AMBER-MIDI-PIONIER and CHARA/CLASSIC-CLIMB), and different wavelengths, from visible to mid-infrared. Combining these observations led us to conclusions that could not be reached taking each of these observations alone. We constrained the radius of the disk rim in the mid-infrared to be 10au. The emission in the near-infrared is extending from the star up to the disk rim, having a high temperature ( 1500K). We postulated that quantum heated particles can be responsible for such a high temperature that far from the star. This points toward a disk that is in a peculiar evolutionary state where the inner disk was accreted onto the star and the rest of the disk is being photo-evaporated by high energy photons from the star.