Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk. (arXiv:2007.15014v1 [astro-ph.EP])

Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk. (arXiv:2007.15014v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ohashi_S/0/1/0/all/0/1">Satoshi Ohashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kataoka_A/0/1/0/all/0/1">Akimasa Kataoka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marel_N/0/1/0/all/0/1">Nienke Van der Marel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hull_C/0/1/0/all/0/1">Charles L. H. Hull</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dent_W/0/1/0/all/0/1">William R. F. Dent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pohl_A/0/1/0/all/0/1">Adriana Pohl</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pinilla_P/0/1/0/all/0/1">Paola Pinilla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dishoeck_E/0/1/0/all/0/1">Ewine F. van Dishoeck</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Henning_T/0/1/0/all/0/1">Thomas Henning</a>

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
$mu$m ALMA observations of polarized dust emission of 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
$sim100$ $mu$m. 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 VLA
observations, we suggest that the thermal emission at 860 $mu$m wavelength is
optically thick ($tau_{rm abs}sim7.3$) at the dust trap with the maximum
observable grain size of $sim100$ $mu$m rather than an optically thin case
with $sim$ cm dust grains. We note that we cannot rule out that larger dust
grains are accumulated near the midplane if the 860 $mu$m thermal emission is
optically thick.

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
$mu$m ALMA observations of polarized dust emission of 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
$sim100$ $mu$m. 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 VLA
observations, we suggest that the thermal emission at 860 $mu$m wavelength is
optically thick ($tau_{rm abs}sim7.3$) at the dust trap with the maximum
observable grain size of $sim100$ $mu$m rather than an optically thin case
with $sim$ cm dust grains. We note that we cannot rule out that larger dust
grains are accumulated near the midplane if the 860 $mu$m thermal emission is
optically thick.

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