Non-Keplerian spirals, a gas-pressure dust trap and an eccentric gas cavity in the circumbinary disc around HD 142527

TL;DR

This study uses ALMA observations to reveal complex non-Keplerian spiral structures, gas pressure traps, and an eccentric cavity in the circumbinary disc around HD 142527, providing insights into disc dynamics and dust trapping mechanisms.

Contribution

First detailed ALMA analysis showing non-Keplerian spirals, vertical gas layer propagation, and an eccentric cavity in HD 142527's circumbinary disc.

Findings

Multiple spiral structures observed in gas tracers.

Detection of a super-Keplerian spiral from the dust horseshoe.

Identification of a gas cavity with eccentricity between 0.3 and 0.45.

Abstract

We present ALMA observations of the $^{12}$CO, $^{13}$CO, C$^{18}$O J=2-1 transitions and the 1.3\,mm continuum emission for the circumbinary disc around HD 142527, at an angular resolution of $\approx$\,0\farcs3. We observe multiple spiral structures in intensity, velocity and velocity dispersion for the $^{12}$CO and $^{13}$CO gas tracers. A newly detected $^{12}$CO spiral originates from the dust horseshoe, and is rotating at super-Keplerian velocity or vertically ascending, whilst the inter-spiral gas is rotating at sub-Keplerian velocities. This new spiral possibly connects to a previously identified spiral, thus spanning > 360$^\circ$. A spatial offset of ~30 au is observed between the $^{12}$CO and $^{13}$CO spirals, to which we hypothesize that the gas layers are propagating at different speeds (``surfing'') due to a non-zero vertical temperature gradient. Leveraging the varying optical depths between the CO isotopologues, we reconstruct temperature and column density maps of the outer disc. Gas surface density peaks at r\,$\approx$\,180\,au, coincident with the peak of continuum emission. Here the dust grains have a Stokes number of $\approx$\,1, confirming radial and azimuthal trapping in the horseshoe. We measure a cavity radius at half-maximum surface density of $\approx$\,100\,au, and a cavity eccentricity between 0.3 and 0.45.