The orbit of HD 142527 B is too compact to explain many of the disc features

Abstract

Context. HD 142527 A is a young and massive Herbig Ae/Be star surrounded by a highly structured disc. The disc shows numerous morphological structures, such as spiral arms, a horseshoe region of dust emission, a set of shadows cast by an inner disc on the outer disc, and a large cavity extending from ≃30 au to ≃130 au. HD 142527 A also has a lower mass companion, HD 142527 B (M = 0.13 ± 0.03 M⊙), which is thought to be responsible for most of the structures observed in the surrounding disc. Aims. We aim to fully constrain the orbit of HD 142527 B and determine whether the binary alone is truly responsible for the observed morphology of the HD 142527 disc. Methods. We gathered VLTI/GRAVITY observations of HD 142527, either from our own programmes or from the ESO archive. We used this inhomogeneous set of data to extract a total of seven high-precision measurements of the relative astrometry between HD 142527 A and B, spread from mid-2017 to early 2021. Combined with what is available in the literature, these new measurements offer a total of 9 yr of astrometric monitoring on HD 142527. We used orbit fitting tools to determine the orbital parameters of HD 142527 B, and used them as inputs for a 3D hydrodynamical model of the disc to determine whether or not the binary is able to create the structures observed in the disc. Results. Our VLTI/GRAVITY astrometry gives excellent constraints on the orbit of HD 142527 B. We show that the secondary is following an orbit of semi-major axis a = 10.80 ± 0.22 au, with moderate eccentricity (e = 0.47 ± 0.01), and has recently passed its periapsis (τ = 2020.42). With such a compact orbit, we show that HD 142527 B can only generate a gap and spiral arms of ~30 au in the disc, which is much smaller than what is revealed by observations. Conclusions. Even from a theoretical standpoint, the observed cavity size of ~ 100 au far exceeds even the most generous predictions for a companion like HD 142527 B on such a compact orbit. Thus, we conclude that the low-mass companion cannot be solely responsible for the observed morphology of the disc surrounding the system.