Protoplanetary Disk Dynamics
Protoplanetary Disks in Star-Disk-Binary Systems
The bulk of my Ph.D. research with Prof. Dong Lai at Cornell was focused on understanding the dynamics of planet-forming warped and eccentric protoplanetary disks with binary companions. I wanted to determine under what conditions the binary's gravitational torque could misalign the host star's spin axis with the disk's orbital angular momentum axis (primordial misalignment), forming planets with orbital planes misaligned with the host star's equatorial plane (spin-orbit misalignment). Generating primordial misalignments with an inclined binary companion's gravitational torque was a leading theory to explain the formation of exoplanets with large stellar obliquities (angle between planet's orbital angular momentum and host star's spin vectors). Key results include:
The formation of a massive, short period planet (hot Jupiter) usually reduces and may completely suppress generation of stellar obliquities from an inclined binary companion.
Under some conditions, an inclined binary companion's torque may make the disk very eccentric (Lidov-Kozai instability).
Viscous torques from disk warping may reduce stellar obliquities over the star-disk-binary system's lifetime.
Recently, I was involved in a collaboration lead by Prof. Simon Albrecht which found a retrograde (greater than 90 deg.) stellar obliquity in the K2 290 planetary system (publ. in PNAS), which confirmed the predictions I made in my works.
Protoplanetary Disks Inclined to Eccentric Binary Stars
With Prof. Dong Lai, I also examined the inclination evolution of protoplanetary disks around eccentric binary stars. The motivation for this work was the few gaseous and debris disks orbiting binary stars that had large inclinations between the disk and binary's orbital planes, which tended to orbit eccentric binaries. I showed gravitational torques from the eccentric binary and viscous torques from disk warping can drive the disk-binary inclination to 90 degrees (polar alignment), explaining the highly inclined circumbinary disks observed. After this work was released, more highly inclined circumbinary disks (such as GW Ori and HD 98800) were detected, thought to be formed through this mechanism.
Recently, Michael Poon (undergraduate CPS and SURP fellow at the University of Toronto) Dr. Wei Zhu (postdoc at CITA, soon to be faculty at Tsinghua University), and I analyzed the KH 15D system, which consists of an inner binary orbited by a warped protoplanetary disk which eclipses the binary as it precesses. Combining photometry and radial velocity data with a dynamical model of the precessing protoplanetary disk, we constrained the disk's annular extent, tilt, and precession period.
Right image credit: Michael Poon
Warped and Extended Circumplanetary Disk/Ring Systems
A number of stars have been observed with deep dips in the star's brightness (such as J1407, PDS 110, and VVV-WIT-07), which have tentatively been interpreted as extended circumplanetary disk/ring systems transiting their host stars. In order for rings to cause a transit signal, some force must stably tilt the rings out of the planet's orbital plane to resist the host star's tidal force. With Prof. Dong Lai, I showed a spining planet with ring self-gravity could stably tilt a circumplanetary disk out to large radii, leading to the transit signals observed. With Jessica Speedie (undergraduate SURP student from McMaster University, now graduate student at University of Victoria), we used N-body integrations to show the equilibrium tilted/warped ring system remained stable over the system's lifetime, but various secular instabilities naturally create gaps in the rings which may be observed.
Image credit: Jessica Speedie
Hjorth M., Albrecht S., Hirano T., Winn J. N., Dawson R. I., Zanazzi J. J., et al., 2021, PNAS, 118, 2017418118. PDF
Michael Poon, J. J. Zanazzi, & Wei Zhu; Constraining the Circumbinary Disk Tilt in the KH 15D system. 2021, MNRAS, 503, 1599. PDF
Jessica Speedie & J. J. Zanazzi; The Stability of Extended Circumplanetary Disk and Ring Systems, with Applications to J1407b. 2020, MNRAS, 497, 1870. PDF
J. J. Zanazzi & Dong Lai; Planet Formation in Disks with Inclined Binary Companions: Can Primordial Spin-Orbit Misalignment be Produced? 2018, MNRAS, 478, 835. PDF
J. J. Zanazzi & Dong Lai; Effect of Disk Warp in Star-Disk-Binary Systems. 2018, MNRAS, 477, 5207. PDF
J. J. Zanazzi & Dong Lai; Inclination Evolution of Protoplanetary Disks around Eccentric Binaries. 2018, MNRAS, 473, 603. PDF
J. J. Zanazzi & Dong Lai; The Lidov-Kozai Effect in Hydrodynamical Disks: Linear Stability Analysis. 2017, MNRAS, 467 (2): 1957-1964. PDF
J. J. Zanazzi & Dong Lai; Extended Transiting Disks and Rings around Giant Planets and Brown Dwarfs: Theoretical Constraints. 2017, MNRAS, 464, 3945. PDF