Mid-infrared observations of the transitional disks around DH Tauri, DM Tauri, and GM Aurigae

Aims. We present mid-infrared observations and photometry of the transitional disks around the young stellar objects DH Tau, DM Tau, and GM Aur, obtained with VISIR/VLT in N band. Our aim is to resolve the inner region and the large-scale structures of these transitional disks, carrying potential signatures of intermediate or later stages of disk evolution and ongoing planet formation. Methods. We use the simultaneously observed standard-stars as PSF reference to constrain the radial flux profiles of our target objects. Subtracting the obtained standard-star profile from the corresponding science object profile yields the flux residuals produced by the star-disk system. A detection threshold takes into account the background standard deviation and also the seeing variations during the observations to evaluate the significance of these flux residuals. On the basis of a simple model for the dust re-emission, we derive constraints on the inner radius of the dust disk. Results. We spatially resolve the transitional disk around GM Aur and determine an inner-disk hole radius of 20.5 +1.0 −0.5 AU. The circumstellar disks around DH Tau and DM Tau are not spatially resolved but we are able to constrain the inner-disk hole radius to <15.5 +9.0 −2.0 AU and <15.5 +0.5 −0.5 AU, respectively. The performed photometry yields fluxes of 178 ± 31 mJy for DH Tau, 56 ± 6m Jy for DM Tau, and 229 ± 14 mJy for GM Aur.