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

<BR /> Aims: We present mid-infrared observations and photometry of the transitional disks around the young stellar objects <ASTROBJ>DH Tau</ASTROBJ>, <ASTROBJ>DM Tau</ASTROBJ>, and <ASTROBJ>GM Aur</ASTROBJ>, 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. <BR /> 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. <BR /> Results: We spatially resolve the transitional disk around GM Aur and determine an inner-disk hole radius of 20.5<SUP>+1.0</SUP><SUB>-0.5</SUB> 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<SUP>+9.0</SUP><SUB>-2.0</SUB> AU and <15.5<SUP>+0.5</SUP><SUB>-0.5</SUB> AU, respectively. The performed photometry yields fluxes of 178 ± 31 mJy for DH Tau, 56 ± 6 mJy for DM Tau, and 229 ± 14 mJy for GM Aur. Based on observations made with ESO Telescopes at the La Silla or Paranal Observatories under programme ID 380.C-0326.