Large dust gaps in the transitional disks of HD 100453 and HD 34282. Connecting the gap size to the spectral energy distribution and mid-infrared imaging

Context. The formation of dust gaps in protoplanetary disks is one of the most important signs of disk evolution and might indicate the formation of planets.
Aims: We aim to characterize the flaring disk structure around the Herbig Ae/Be stars HD 100453 and HD 34282. Their spectral energy distributions (SEDs) show an emission excess between 15-40 μm, but very weak (HD 100453) and no (HD 34282) signs of the 10 and 20 μm amorphous silicate features. We investigate whether this implies the presence of large dust gaps.
Methods: We investigated spatially resolved mid-infrared Q-band images taken with Gemini North/MICHELLE. We performed radiative transfer modeling and examined the radial distribution of dust. We simultaneously fit the Q-band images and SEDs of HD 100453 and HD 34282.
Results: Our solutions require that the inner halos and outer disks be separated by large dust gaps that are depleted with respect to the outer disk by a factor of 1000 or more. The inner edges of the outer disks of HD 100453 and HD 34282 have temperatures of ~160 ± 10 K and ~60 ± 5 K, respectively. Because of the high surface brightness of these walls, they dominate the emission in the Q band. Their radii are constrained at 20_-2⁺² AU and 92_-17⁺³¹ AU, respectively.
Conclusions: HD 100453 and HD 34282 most likely have disk dust gaps. The upper limit of the dust mass in each gap is estimated to be about 10^-7 M_⊙. We find that the locations and sizes of disk dust gaps are connected to the SED, as traced by the mid-infrared flux ratio F₃₀/F_13.5. We propose a new classification scheme for the Meeus groups based on the F₃₀/F_13.5 ratio. The absence of amorphous silicate features in the observed SEDs is caused by the depletion of small (≲1 μm) silicate dust at temperatures above ≳160 K, which could be related to the presence of a dust gap in that region of the disk.