SIMBAD references

The processes that form transition disks–disks with depleted inner regions–are not well understood; possible scenarios include planet formation, grain growth, and photoevaporation. Disks with spatially resolved dust holes are rare, but, in general, even less is known about the gas structure. The disk surrounding the A0 star Oph IRS 48 in the nearby ρ Ophiuchus region has a 30 AU radius hole previously detected in the 18.7 µm dust continuum and in warm CO in the 5 µm fundamental rovibrational band. We present here Submillimeter Array 880 µm continuum imaging resolving an inner hole. However, the radius of the hole in the millimeter dust is only 13 AU, significantly smaller than measured at other wavelengths. The nesting structure of the disk is counter intuitive, with increasingly large radius rings of emission seen in the millimeter dust (12.9^+1.7_–3.4AU), 5 µm CO (30 AU), and 18.7 µm dust (peaking at 55 AU). We discuss possible explanations for this structure, including self-shadowing that cools the disk surface layers, photodissociation of CO, and photoevaporation. However, understanding this unusual disk within the stringent multi-wavelength spatial constraints will require further observations to search for cold atomic and molecular gas.