The evolutionary state of young protoplanetary disks

Observations of protoplanetary disks have been focused on low-mass, classical T-Tauri stars and on intermediate mass Herbig Ae/Be stars. The observations of the Herbig stars have introduced a bias in the intermediate mass range since they exclude the earlier stages of disk evolution. The heaviest T-Tauri stars, the intermediate mass T-Tauri stars (IMTT stars), with spectral type from F to early K and with masses ≥1.5 M_☉, are the younger precursors of the Herbig stars. To get a complete picture of the evolution of protoplanetary disks IMTT stars needs to be studied. Many IMTT stars have already been included in samples of classical T-Tauri stars where they are the most massive stars in the samples. This thesis seeks to remove some of this bias by focusing on the IMTT stars and observations of the disks around them.
This thesis presents the research of a sample of 49 identified IMTT stars with infrared access. Their disks are compared with those of the known Herbig Ae/Be stars to examine their evolutionary status.
The thesis also presents spatially resolved near-infrared scattered light observations of the IMTT star RY Tau. Using radiative transfer modelling the observations are recreated and features reminiscent of a dusty disk wind is assessed.
Finally, it presents near-infrared spatially resolved scattered light observations of 23 optically bright stars in the Orion high mass star forming region. The observations are analysed in context of the stellar parameters, stellar multiplicity and the environment of a high star forming region.