Detection of Sharp Symmetric Features in the Circumbinary Disk Around AK Sco

TL;DR

This paper reports the discovery of sharp, symmetric features in the circumbinary disk around AK Sco, revealing complex structures possibly caused by planetary interactions, using high-contrast imaging with SPHERE.

Contribution

First direct imaging detection of sharp features in a circumbinary disk around AK Sco, suggesting eccentric or spiral structures influenced by planets.

Findings

Detected resolved scattered light emission from AK Sco's disk

Identified sharp symmetric features possibly caused by planets

Proposed interpretations include eccentric ring or spiral arms

Abstract

The Search for Planets Orbiting Two Stars (SPOTS) survey aims to study the formation and distribution of planets in binary systems by detecting and characterizing circumbinary planets and their formation environments through direct imaging. With the SPHERE Extreme Adaptive Optics instrument, a good contrast can be achieved even at small (<300 mas) separations from bright stars, which enables studies of planets and disks in a separation range that was previously inaccessible. Here, we report the discovery of resolved scattered light emission from the circumbinary disk around the well-studied young double star AK Sco, at projected separations in the ~13--40 AU range. The sharp morphology of the imaged feature is surprising, given the smooth appearance of the disk in its spectral energy distribution. We show that the observed morphology can be represented either as a highly eccentric ring around AK Sco, or as two separate spiral arms in the disk, wound in opposite directions. The relative merits of these interpretations are discussed, as well as whether these features may have been caused by one or several circumbinary planets interacting with the disk.