Scattered light mapping of protoplanetary disks

Abstract

Context. High-contrast scattered light observations have revealed the surface morphology of several dozen protoplanetary disks at optical and near-infrared wavelengths. Inclined disks offer the opportunity to measure part of the phase function of the dust grains that reside in the disk surface which is essential for our understanding of protoplanetary dust properties and the early stages of planet formation. Aims. We aim to construct a method which takes into account how the flaring shape of the scattering surface of an optically thick protoplanetary disk projects onto the image plane of the observer. This allows us to map physical quantities (e.g., scattering radius and scattering angle) onto scattered light images and retrieve stellar irradiation corrected images (r 2 -scaled) and dust phase functions. Methods. The scattered light mapping method projects a power law shaped disk surface onto the detector plane after which the observed scattered light image is interpolated backward onto the disk surface. We apply the method on archival polarized intensity images of the protoplanetary disk around HD 100546 that were obtained with VLT/SPHERE in the R band and VLT/NACO in the H and K s bands. Results. The brightest side of the r 2 -scaled R band polarized intensity image of HD 100546 changes from the far to the near side of the disk when a flaring instead of a geometrically flat disk surface is used for the r 2 -scaling. The decrease in polarized surface brightness in the scattering angle range of ∼40• -70• is likely a result of the dust phase function and degree of polarization which peak in different scattering angle regimes. The derived phase functions show part of a forward scattering peak, which indicates that large, aggregate dust grains dominate the scattering opacity in the disk surface. Conclusions. Projection effects of a protoplanetary disk surface need to be taken into account to correctly interpret scattered light images. Applying the correct scaling for the correction of stellar irradiation is crucial for the interpretation of the images and the derivation of the dust properties in the disk surface layer.

The Complex Morphology of the Young Disk MWC 758: Spirals and Dust Clumps around a Large Cavity

“…Future CO emission lines observations with a better angular resolution and sensitivity, perhaps using higher rotational lines, will help to constrain the velocity structure in the cavity. This case can be compared to the disk HD 135344B which also probably has a mildly inner warped disk (Stolker et al 2016). It is different of the binary system HD 142527, which contains a strongly warped disk, by 70…”

“…With the the possible presence of a warped inner disc in MWC 758 projecting shadows in the outer regions, this possibility has not to be discarded. Indeed, the two other disks which are known to feature an inner warped disk, HD 135344B and HD 142527, also have a large cavity and spirals (Stolker et al 2016;Christiaens et al 2014;Casassus et al 2015a). It is also still unclear if a planet inside the cavity, with a non-coplanar or eccentric orbit, might produce such spirals.…”

Spirals in protoplanetary disks from photon travel time

“…(10) should be observable in such images. During the preparation of this manuscript, Stolker et al (2016) reported a curved shadow in the HD 135344 B disk and determined that it is well fitted by the flat-disk shadow as described by Eq. (1).…”

“…Grady et al 2001;Hashimoto et al 2011;Boccaletti et al 2013;Grady et al 2013;Avenhaus et al 2014;Benisty et al 2015;Wagner et al 2015;Stolker et al 2016) and there is much interest in understanding their origins, which might be perturbations by giant planets, disk-envelope interactions, instabilities, or other phenomena. We present a new mechanism for creating scattered-light spirals: the finite speed of light can cause a shadow from the inner disk to morph into a spiral, with properties determined by the disk and viewing geometry, and the orbital motion of the shadowing clump.…”

A Multi-wavelength Analysis of Dust and Gas in the SR 24S Transition Disk

“…Recent multi-wavelength observations of protoplanetary disks revealed astonishing structures, such as concentric dust rings, spiral arms, and asymmetries (e.g., van der Marel et al 2013; ALMA Partnership et al 2015;Casassus et al 2015;Andrews et al 2016;de Boer et al 2016;Ginski et al 2016;Pérez et al 2016;Stolker et al 2016;Fedele et al 2017). These observations suggest that significant evolution has taken place and that probably planets have already imprinted their existence in the parental disks.…”