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 \rho Ophiuchus region has a 30 AU radius hole previously detected in the 18.7 \mu m dust continuum and in warm CO in the 5 \mu m fundamental ro-vibrational band .
We present here Submillimeter Array 880 \mu m 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 radii rings of emission seen in the millimeter dust ( 12.9 ^ { +1.7 } _ { -3.4 } AU ) , 5 \mu m CO ( 30 AU ) and 18.7 \mu m 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 .