A Cavity of Large Grains in the Disk Around the Group II Herbig Ae/Be Star HD 142666

TL;DR

This study models the disk around the Group II Herbig Ae/Be star HD 142666, revealing a cavity of large grains that suggests some Group II disks may also have large grain cavities, challenging previous assumptions.

Contribution

The paper presents the first evidence of a large grain cavity in a Group II Herbig Ae/Be star disk through combined modeling and ALMA observations.

Findings

Disk modeling indicates a large grain depletion out to ~16 au.

The disk shows a high degree of dust settling consistent with Group II classification.

Results suggest some Group II disks may have large grain cavities.

Abstract

Herbig Ae/Be (HAeBe) stars have been classified into Group I or Group II, which were initially thought to be flared and flat disks, respectively. Several Group I sources have been shown to have large gaps, suggesting ongoing planet formation, while no large gaps have been found in the disks of Group II sources. We analyzed the disk around the Group II source, HD 142666, using irradiated accretion disk modeling of the broad-band spectral energy distribution along with the 1.3 millimeter spatial brightness distribution traced by Atacama Large Millimeter and Submillimeter Array (ALMA) observations. Our model reproduces the available data, predicting a high degree of dust settling in the disk, which is consistent with the Group II classification of HD 142666. In addition, the observed visibilities and synthesized image could only be reproduced when including a depletion of large grains out to ~16 au in our disk model, although the ALMA observations did not have enough angular resolution to fully resolve the inner parts of the disk. These results may suggest that some disks around Group II HAeBe stars have cavities of large grains as well. Further ALMA observations of Group II sources are needed to discern how commonly cavities occur in this class of objects, as well as to reveal their possible origins.