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

Joanna M. Brown, Katherine A. Rosenfeld, Sean M. Andrews, David J. Wilner, Ewine F. van Dishoeck

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.

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

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.

Paper Structure

This paper contains 8 sections, 3 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Observations and Results
  3. Modeling
  4. Discussion
  5. Scenario 1
  6. Scenario 2
  7. Scenario 3
  8. Conclusions

Figures (2)

  • Figure 1: Images of the data (left), model (center left) and residuals (center right). The contours are 3$\sigma$ intervals where the RMS noise is 2.7 mJy/beam. The (u,v) visibities for 345 GHz (black) and 230 GHz (gray) are on the far right with the best fit model from Table \ref{['table:model']} in red.
  • Figure 2: The radial distribution of flux from the millimeter dust (black), 5 $\mu$m CO (red) and 18.7 $\mu$m dust (blue). The millimeter profile is the best fit profile listed in Table \ref{['table:model']} with the grey region representing fits within the error bars. The 5 $\mu$m CO profile is the best fit model from brown12 Figure 8. The 18.7 $\mu$m dust flux is a cut along the major axis of the geers07 VISIR image after 2-D maximum likelihood deconvolution of the PSF.