Planet Obliquities

VHS 1256 b is a 12-16 Jupiter-mass companion on a Tatooine-like orbit around a low-mass binary. We constrain the planet obliquity, which is the orientation between the planet spin axis and orbit normal, to be 90 +/- 25 deg. This "sideways-spinning" companion is reminiscent of Uranus' 98 deg. obliquity, although we find that their origin stories are very different. Check out our paper to find out why!

Michael Poon, Marta Bryan, Hanno Rein, et al.; Leaning Sideways: VHS 1256-1257 b is a Super-Jupiter with a Uranus-like Obliquity, published in The Astronomical Journal

We speculate about whether exomoons could push planets in multi-planetary system onto a high obliquity state -- the answer is yes! The exomoon helps with tilting the planet because it acts like a lever, thus enhancing a spin-orbit resonance. This idea is quite general, and we apply it specifically to β Pictoris b where an upcoming JWST observation will constrain the planet's obliquity.

Michael Poon, Hanno Rein, Dang Pham; A potential exomoon from the predicted planet obliquity of β Pictoris b, published in the Open Journal of Astrophysics

Binary Stars and Circumbinary Disks

KH 15D is known as the 'winking star' due to its peculiar dips in brightness over monthly and yearly timescales. The leading hypothesis is that this binary star hosts a circumbinary disk, which is warped due to the torque from its host binary. As this disk wobbles, it can block the light from one or both stars, leading to its unusual light curve. We analyzed how this light changed over the past 60 years, and used secular dynamics to build a self-consistent warped disk model to constrain the disk size, warp, and twist (code here). My favourite part of this project is what comes after -- inspired by the uniqueness of KH 15D, Klaus Bernhard, an amateur astronomy from Austria, finds two new systems similar to KH 15D! 

Luke Lamitina, Lynne Hillenbrand,  & Michael Poon; Continued Photometric Monitoring Supports Long-term Dynamical Evolution in the Young Binary Star–Disk System KH 15D, AJ, 2025

Michael Poon, J. J. Zanazzi, & Wei Zhu; Constraining the Circumbinary Disk Tilt in the KH 15D system, MNRAS, 2021

Wei Zhu, et al. (including Michael Poon); Two Candidate KH 15D-like Systems frfaom the Zwicky Transient Facility, ApJL, 2022 (initiated by citizen science!)

Related press: https://www.artsci.utoronto.ca/news/team-astronomers-adds-very-short-list-rare-binary-star-systems

Below is a poster I presented at an undergrad research fair at CITA in August 2019.