Revealing the sub-AU asymmetries of the inner dust rim in the disk around the Herbig Ae star R CrA

TL;DR

This study uses VLTI/AMBER interferometry to reveal highly asymmetric, sub-AU scale dust disk structures around the Herbig Ae star R CrA, supporting the puffed-up inner rim model with large dust grains.

Contribution

First direct interferometric evidence of asymmetric inner dust rims in Herbig Ae disks, supporting the puffed-up rim model with detailed geometric and physical modeling.

Findings

Detected a highly asymmetric brightness distribution.

Supported the puffed-up inner rim model with curved shape.

Identified large (>1.2 micron) silicate dust grains.

Abstract

Models predict that in the innermost AU of the disk around Herbig Ae/Be star, the dust disk forms a "puffed-up" inner rim, which should result in a strongly asymmetric brightness distribution for disks seen under intermediate inclination. Using the VLTI/AMBER long-baseline interferometer, we obtained 24 near-infrared (H- and K-band) spectro-interferometric observations on the Herbig Ae star R CrA. In the derived visibility function, we detect the signatures of an extended (25 mas) and a compact component (5.8 mas), with the compact component contributing about 2/3 of the total flux. The brightness distribution is highly asymmetric, as indicated by the strong closure phases (up to 40 deg) and the detected position angle dependence of the visibilities and closure phases. To interpret these asymmetries, we employ geometric as well as physical models, including a binary model, a skewed ring model, and a puffed-up inner rim model with a vertical or curved rim shape. Our curved puffed-up rim model can reasonably well reproduce the interferometric observables and the SED simultaneously and suggests a luminosity of 29 L_sun and the presence of relatively large (> 1.2 micron) Silicate dust grains. Perpendicular to the disk, two bow shock-like structures appear in the associated reflection nebula NGC 6729, suggesting that the resolved sub-AU size disk is the driving engine of a large-scale outflow. Detecting, for the first time, strong non-localized asymmetries in the inner regions of a Herbig Ae disk, our study supports the existence of a puffed-up inner rim in YSO disks.