Spiral arms in the proto-planetary disc HD100453 detected with ALMA: evidence for binary-disc interaction and a vertical temperature gradient

TL;DR

This study uses high-resolution ALMA observations to reveal spiral arms in the HD100453 proto-planetary disc, providing evidence of binary interaction and a vertical temperature gradient affecting spiral morphology.

Contribution

First detection of sub-mm continuum counterparts to scattered light spirals in HD100453, linking spiral structures to a binary companion and demonstrating the importance of vertical temperature gradients.

Findings

Spiral arms are observed in both scattered light and sub-mm continuum.

The companion star is responsible for launching the observed spirals.

A vertical temperature gradient explains differences in spiral pitch angles.

Abstract

Scattered light high-resolution imaging of the proto-planetary disc orbiting HD100453 shows two symmetric spiral arms, possibly launched by an external stellar companion. In this paper we present new, sensitive high-resolution ($\sim$30 mas) Band 7 ALMA observations of this source. This is the first source where we find counterparts in the sub-mm continuum to both scattered light spirals. The CO J=3-2 emission line also shows two spiral arms; in this case they can be traced over a more extended radial range, indicating that the southern spiral arm connects to the companion position. This is clear evidence that the companion is responsible for launching the spirals. The pitch angle of the sub-millimeter continuum spirals ($\sim 6 ^{\circ}$) is lower than the one in scattered light ($\sim 16 ^{\circ}$). We show that hydrodynamical simulations of binary-disc interaction can account for the difference in pitch angle only if one takes into account that the midplane is colder than the upper layers of the disc, as expected for the case of externally irradiated discs.