The gas-dust transition region in young stellar objects: a sub-milli-arcsecond view through the eyes of CHARA

Using the sub-milli-arcsecond resolution of the CHARA interferometer array and combining light with the 2-telescope combiner CHARA Classic,we have detected strong near-infrared (NIR) emission interior to the dust-sublimation radius of Herbig Ae stars MWC275 and AB Aur. The large contribution of this emission component, which we argue to be hot gas,to the total NIR spectral energy distribution (SED) is not predicted by current models of the dust evaporation front, indicating that the NIR disk is more complicated than expected. Furthermore, we demonstrate that the structure of the evaporation front in MWC275 is time variable,making single epoch, large uv coverage observations critical to decoding front geometry. With the commissioning of CHARA Michigan Phase Tracker in the summer of 2008, the Michigan Infrared Combiner (a 6 telescope combiner at CHARA) will become an ideal instrument for studying the evaporation front, achieving the required sensitivities to begin the first "true" interferometric imaging of the gas-dust transition region in young stellar objects (YSOs). Here, we summarize results on the evaporation front structure obtained with CHARA Classic and describe future prospects with CHARA MIRC in elucidating morphology of the gas-dust transition region.