Earth, Moon, Sun, and CV Accretion Disks

TL;DR

This paper develops a theoretical model for retrograde precession in misaligned, spinning accretion disks, demonstrating its consistency with simulations and observations, and highlighting the role of tidal torques and disk geometry.

Contribution

It provides a generic theoretical expression for precession in misaligned disks, linking it to Earth's precession and applying it to various astrophysical systems.

Findings

Theoretical expression matches Earth's equinox precession.

Precession best described by a differentially rotating, tilted disk with an inner tilted ring.

Model agrees with numerical simulations and observations of systems with main sequence secondaries.

Abstract

Net tidal torque by the secondary on a misaligned accretion disk, like the net tidal torque by the Moon and the Sun on the equatorial bulge of the spinning and tilted Earth, is suggested by others to be a source to retrograde precession in non-magnetic, accreting Cataclysmic Variable (CV) Dwarf Novae systems that show negative superhumps in their light curves. We investigate this idea in this work. We generate a generic theoretical expression for retrograde precession in spinning disks that are misaligned with the orbital plane. Our generic theoretical expression matches that which describes the retrograde precession of Earths' equinoxes. By making appropriate assumptions, we reduce our generic theoretical expression to those generated by others, or to those used by others, to describe retrograde precession in protostellar, protoplanetary, X-ray binary, non-magnetic CV DN, quasar and black hole systems. We find that differential rotation and effects on the disk by the accretion stream must be addressed. Our analysis indicates that the best description of a retrogradely precessing spinning, tilted, CV DN accretion disk is a differentially rotating, tilted disk with an attached rotating, tilted ring located near the innermost disk annuli. Our final, reduced expression for retrograde precession agrees well with our numerical simulation results and with selective observational systems that seem to have main sequence secondaries. Our results suggest that tidal torques should be common to a variety of systems where one member is spinning and tilted, regardless if accretion disks are present or not. Our results suggest that the accretion disk's geometric shape directly affects the disk's precession rate.