A tale of two Herbig Ae stars, MWC 275 and AB Aurigae: comprehensive models for spectral energy distribution and interferometry

We present comprehensive models for the Herbig Ae stars MWC 275 and AB Aur that aim to explain their spectral energy distribution (from UV to millimeter) and long-baseline interferometry (from near-infrared to millimeter) simultaneously. Data from the literature, combined with new mid-infrared (MIR) interferometry from the Keck Segment Tilting Experiment, are modeled using an axisymmetric Monte Carlo radiative transfer code. Models in which most of the near-infrared (NIR) emission arises from a dust rim fail to fit the NIR spectral energy distribution (SED) and sub-milliarcsecond NIR CHARA interferometry. Following recent work, we include an additional gas emission component with similar size scale to the dust rim, inside the sublimation radius, to fit the NIR SED and long-baseline NIR interferometry on MWC 275 and AB Aur. In the absence of shielding of starlight by gas, we show that the gas-dust transition region in these YSOs will have to contain highly refractory dust, sublimating at ~1850 K. Despite having nearly identical structure in the thermal NIR, the outer disks of MWC 275 and AB Aur differ substantially. In contrast to the AB Aur disk, MWC 275 lacks small grains in the disk atmosphere capable of producing significant 10-20 μm emission beyond ~7 AU, forcing the outer regions into the "shadow" of the inner disk