Letter to the Editor

Peering through the disc of HD 98800 BaBb

Precise timing predictions for the HD 98800 AaAb occultation

¹ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C 4000 Liège, Belgium
² European Southern Observatory, Karl-Schwarzschild-Str. 2 85748 Garching bei München, Germany
³ Astronomy Unit, Department of Physics and Astronomy, Queen Mary University of London, Mile End Road London E1 4NS, United Kingdom

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 11 June 2026
Accepted: 11 July 2026

Abstract

Context. The young hierarchical quadruple system HD 98800 is composed of the tight binaries AaAb and BaBb on a wide, highly inclined outer orbit. The B subsystem hosts a circumbinary disc in a polar configuration, and the geometry of the system offers a rare opportunity to observe the passage of the disc around BaBb in front of AaAb.

Aims. We update the overall orbital solution to offer precise time windows of the main occultation features by combining the orbit based on the most recent knowledge of the disc structure.

Methods. We combined new and published radial velocity measurements and multi-wavelength astrometry for the outer AB orbit and the two inner subsystems, AaAb and BaBb, in a joint orbital fit.

Results. The revised solution is consistent with previous dynamical masses and improves the outer orbit, reducing the uncertainties in the period and periastron epoch by about a factor of two. It also narrows the predicted crossing-phase windows to 5–15 days at the 1σ level, improving the timing of ingress, egress, and the first cavity-crossing predictions.

Conclusions. These results provide a more accurate timing framework for future observations of the occultation, although the predicted epochs remain model-dependent because of uncertainties in the disc structure.