High-Contrast NIR Polarization Imaging of MWC480

TL;DR

This study uses high-contrast NIR polarization imaging to analyze the structure of the MWC 480 protoplanetary disk, revealing it to be significantly flatter than typical transitional disks, indicating advanced grain growth and settling.

Contribution

First polarimetric imaging of MWC 480 in the H band constrains the disk's flattening and compares it with gas disk properties, providing insights into disk evolution.

Findings

Disk detected from 27.4 to 137 AU in scattered light.

Disk's opening angle constrained between 1.3° and 2.2°.

Dust disk is 5-7 times flatter than transitional disks.

Abstract

One of the key predictions of modeling from the IR excess of Herbig Ae stars is that for protoplanetary disks, where significant grain growth and settling has occurred, the dust disk has flattened to the point that it can be partially or largely shadowed by the innermost material at or near the dust sublimation radius. When the self-shadowing has already started, the outer disk is expected to be detected in scattered light only in the exceptional cases that the scale height of the dust disk at the sublimation radius is smaller than usual. High-contrast imaging combined with the IR spectral energy distribution allow us to measure the degree of flattening of the disk, as well as to determine the properties of the outer disk. We present polarimetric differential imaging in $H$ band obtained with Subaru/HiCIAO of one such system, MWC 480. The HiCIAO data were obtained at a historic minimum of the NIR excess. The disk is detected in scattered light from 0\farcs2-1\farcs0 (27.4-137AU). Together with the marginal detection of the disk from 1998 February 24 by HST/NICMOS, our data constrain the opening half angle for the disk to lie between 1.3$\leq\theta\leq 2.2^\circ$. When compared with similar measures in CO for the gas disk from the literature, the dust disk subtends only $\sim$30% of the gas disk scale height (H/R$\sim$0.03). Such a dust disk is a factor of 5-7 flatter than transitional disks, which have structural signatures that giant planets have formed.