Solving Grain Size Inconsistency between ALMA Polarization and VLA Continuum in the Ophiuchus IRS 48 Protoplanetary Disk

The Astrophysical Journal, vol. 900, pp. 81

Abstract

Abstract The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub)millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 μm ALMA observations of polarized dust emission from this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1%–2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼100 μm. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both ALMA polarization and previous ALMA and Very Large Array observations, we suggest that the thermal emission at 860 μm wavelength is optically thick (τ abs ∼ 7.3) at the dust trap with a maximum observable grain size of ∼100 μm rather than an optically thin case with centimeter-sized dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 μm thermal emission is optically thick.

Authors 9

1. Satoshi Ohashi corresponding

   RIKEN

   Affiliation as printed

   RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan; satoshi.ohashi@riken.jp

   RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan

2. Akimasa Kataoka

   The Graduate University for Advanced Studies, SOKENDAI · National Astronomical Observatory of Japan

   Affiliation as printed

   Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

   National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan

3. Nienke van der Marel

   University of Victoria

   Affiliation as printed

   Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada

4. Charles L. H. Hull

   Atacama Large Millimeter Submillimeter Array · National Astronomical Observatory of Japan

   Affiliation as printed

   Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile

   National Astronomical Observatory of Japan, NAOJ Chile, Alonso de Córdova 3788, Office 61B, 7630422, Vitacura, Santiago, Chile

5. William R. F. Dent

   Atacama Large Millimeter Submillimeter Array

   Affiliation as printed

   Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile

6. A. Pohl

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

7. Paola Pinilla

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

8. Ewine F. van Dishoeck Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands

9. Thomas K. Henning

   Max Planck Institute for Astronomy

   Affiliation as printed

   Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany