An unbiased SPHERE-IFS Survey of Nearby Herbig Ae/Be Stars: Are All Group I Disks Transitional?

Maaskant et al. (2013) have proposed a model in which the Herbig Ae/Be stars with the strongest far-infrared excesses (the Meeus et al. Group I sources) have large disk gaps (possibly opened by newly formed planets) and may thus be considered transitional. One strong prediction from this model is that the Group I sources should have a larger spatial extent (as seen in scattered light) than the Group II Herbig stars. Giving constraints on the existence of gaps is important also for the evolution of the inner disk, particularly concerning the study of the disk accretion. We have developed a novel algorithm (SADI) for the removal of speckles from near-infrared VLT/SPHERE Integral Field Spectrograph (IFS) data, based on the wavelength-dependent position of speckles and the independence from it of real features (disks asymmetries and companions). This algorithm allowed us to detect so far four new companion candidates and six disk structures in a sample of 23 nearby Herbig stars. The ratio between the number of disk detections over the total number of Group I and Group II targets are found to be significantly different, in agreement with the expectations from the Maaskant et al. model.