2021MNRAS.504..782G

We present ALMA observations of the ¹²CO, ¹³CO, C¹⁸O J = 2-1 transitions and the 1.3 mm continuum emission for the circumbinary disc around HD 142527, at an angular resolution of ≃ 0_.^′′3. We observe multiple spiral structures in intensity, velocity, and velocity dispersion for the ¹²CO and ¹³CO gas tracers. A newly detected ¹²CO spiral originates from the dust horseshoe, and is rotating at super-Keplerian velocity or vertically ascending, whilst the interspiral gas is rotating at sub-Keplerian velocities. This new spiral possibly connects to a previously identified spiral, thus spanning >360°. A spatial offset of 30 au is observed between the ¹²CO and ¹³CO 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 ≃ 180 au, coincident with the peak of continuum emission. Here, the dust grains have a Stokes number of ≃ 1, confirming radial and azimuthal trapping in the horseshoe. We measure a cavity radius at half-maximum surface density of ≃ 100 au, and a cavity eccentricity between 0.3 and 0.45.