Matryoshka Holes: Nested Emission Rings in the Transitional Disk Oph IRS 48

TL;DR

This study reveals a complex, nested emission ring structure in the transition disk Oph IRS 48, with varying radii across different wavelengths, challenging existing models of disk evolution.

Contribution

It provides high-resolution submillimeter imaging of the disk, uncovering a counter-intuitive nested structure across multiple wavelengths, and discusses potential physical explanations.

Findings

Inner hole in millimeter dust is smaller than at other wavelengths.

Disks show increasingly large emission radii at longer wavelengths.

The nested structure suggests complex physical processes in disk evolution.

Abstract

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 A0 star Oph IRS 48 in the nearby Rho Ophiuchus region has a 30 AU radius hole previously detected in the 18.7 micron dust continuum and in warm CO in the 5 micron fundamental ro-vibrational band. We present here Submillimeter Array 880 micron 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 micron CO (30 AU) and 18.7 micron 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.