Shadowing and multiple rings in the protoplanetary disk of HD 139614

TL;DR

This study models the protoplanetary disk around HD 139614, revealing that multiple misaligned zones or a warp, possibly caused by an inclined planetary companion, explain observed shadows and asymmetries in scattered light images.

Contribution

First detailed scattered light observations and modeling of HD 139614's disk, demonstrating that multiple misaligned zones explain shadow features, suggesting possible planetary influence.

Findings

Broad shadow spans ~240° in the outer disk.

Multiple misaligned zones are needed to explain shadows.

A planetary companion may cause the warp and dust gap.

Abstract

Shadows in scattered light images of protoplanetary disks are a common feature and support the presence of warps or misalignments between disk regions. These warps are possibly due to an inclined (sub-)stellar companion embedded in the disk. We study the morphology of the protoplanetary disk around the Herbig Ae star HD 139614 based on the first scattered light observations of this disk, which we model with the radiative transfer code MCMax3D. We obtained J- and H-band observations in polarized scattered light with VLT/SPHERE that show strong azimuthal asymmetries. In the outer disk, beyond ~30 au, a broad shadow spans a range of ~240{\deg} in position angle, in the East. A bright ring at ~16 au also shows an azimuthally asymmetric brightness, with the faintest side roughly coincidental with the brightest region of the outer disk. Additionally, two arcs are detected at ~34 au and ~50 au. We created a simple 4-zone approximation to a warped disk model of HD 139614 in order to qualitatively reproduce these features. The location and misalignment of the disk components were constrained from the shape and location of the shadows they cast. We find that the shadow on the outer disk covers a range of position angle too wide to be explained by a single inner misaligned component. Our model requires a minimum of two separate misaligned zones -- or a continuously warped region -- to cast this broad shadow on the outer disk. A small misalignment of ~4{\deg} between adjacent components can reproduce most of the observed shadow features. Multiple misaligned disk zones, potentially mimicing a warp, can explain the observed broad shadows in the HD 139614 disk. A planetary mass companion in the disk, located on an inclined orbit, could be responsible for such a feature and for the dust depleted gap responsible for a dip in the SED.