Mid-InfraRed imaging of the circumstellar dust around three Herbig Ae   stars : HD135344, CQTau, HD163296
  Planet formation has been known for many years to be tied to the spatial distribution of gas and dust in disks around young stars. To constrain planet formation models, imaging observations of protoplanetary disks are required. In this framework, we have undertaken a mid-infrared imaging survey of Herbig Ae stars, which are pre-main sequence stars of intermediate mass still surrounded by a large amount of circumstellar material. The observations were made at a wavelength of 20.5 $\mu$m with the CAMIRAS camera mounted at the Cassegrain focus of the Canada France Hawaii Telescope.   We report the observations of three stars, HD135344, CQTau and HD163296. The circumstellar material around the three objects is spatially resolved. The extensions feature a disk like shape. The images provide direct information on two key parameters of the disk : its inclination and its outer radius. The outer radius is found to be quite different from the one deduced from disk models only constrained by fitting the Spectral Energy Distribution of the object. Other parameters of the disk, such as flaring, dust mass have been deduced from fitting both the observed extension and the spectral energy distribution with sophisticated disk models.   Our results show how important imaging data are to tighten constraints on the disk model parameters. 
C. Doucet (CEA Sap), E. Pantin (CEA Sap), P.O. Lagage (CEA Sap), C. P.   Dullemond (MPIA)