Constraining the Gap Size in the Disk around HD 100546 in the Mid-infrared

We refine the gap size measurements of the disk surrounding the Herbig Ae star HD 100546 in the N band. Our new mid-infrared interferometric (MIDI) data have been taken with the UT baselines and span the full range of orientations. The correlated fluxes show a wavy pattern in which the minima separation links to a geometrical structure in the disk. We fit each correlated flux measurement with a spline function, deriving the corresponding spatial scale, while assuming that the pattern arises interferometrically due to the bright emission from the inner disk and the opposing sides of the wall of the outer disk. We then fit an ellipse to the derived separations at their corresponding position angles, thereby using the observations to constrain the disk inclination to i = 47° ± 1° and the disk position angle to PA = 135.°0 ± 2.°5 east of north, both of which are consistent with the estimated values in previous studies. We also derive the radius of the ellipse to 15.7 ± 0.8 au. To confirm that the minima separations translate to a geometrical structure in the disk, we model the disk of HD 100546 using a semianalytical approach taking into account the temperature and optical depth gradients. Using this model, we simultaneously reproduce the level and the minima of the correlated fluxes and constrain the gap size of the disk for each observation. The values obtained for the projected gap size in different orientations are consistent with the separation found by the geometrical model.