Verhoeff, A. P × Min, M Acke, Bram van Boekel, R Pantin, E Waters, L. B. F. M Tielens, A. G. G. M van den Ancker, M. E Mulders, G. D de Koter, Alex Bouwman, J #
Edp sciences s a
Astronomy & astrophysics vol:516 pages:1-9
Context. Based on the far infrared excess the Herbig class of stars is divided into a group with flaring circumstellar disks (group I) and a group with flat circumstellar disks (group II). Dust sedimentation is generally proposed as an evolution mechanism to transform flaring disks into flat disks. Theory predicts that during this process the disks preserve their gas content, however observations of group II Herbig Ae stars demonstrate a lack of gas.