Coevolution of Binaries and Gaseous Discs

TL;DR

This study uses hydrodynamic simulations to explore how binary star systems and their surrounding gaseous discs influence each other's evolution, revealing the impact of binary eccentricity on disc structure and binary orbital decay.

Contribution

It provides new insights into the coevolution of binaries and circumbinary discs, especially how binary eccentricity affects disc dynamics and binary orbital decay.

Findings

Eccentric binaries cause stronger disc coupling and eccentricity growth.

Nearly circular binaries weakly excite disc eccentricity through parametric instability.

All systems show binary semimajor axis decay due to viscous dissipation.

Abstract

The recent discoveries of circumbinary planets by $\it Kepler$ raise questions for contemporary planet formation models. Understanding how these planets form requires characterizing their formation environment, the circumbinary protoplanetary disc, and how the disc and binary interact and change as a result. The central binary excites resonances in the surrounding protoplanetary disc that drive evolution in both the binary orbital elements and in the disc. To probe how these interactions impact binary eccentricity and disc structure evolution, N-body smooth particle hydrodynamics (SPH) simulations of gaseous protoplanetary discs surrounding binaries based on Kepler 38 were run for $10^4$ binary periods for several initial binary eccentricities. We find that nearly circular binaries weakly couple to the disc via a parametric instability and excite disc eccentricity growth. Eccentric binaries strongly couple to the disc causing eccentricity growth for both the disc and binary. Discs around sufficiently eccentric binaries that strongly couple to the disc develop an $m = 1$ spiral wave launched from the 1:3 eccentric outer Lindblad resonance (EOLR) that corresponds to an alignment of gas particle longitude of periastrons. All systems display binary semimajor axis decay due to dissipation from the viscous disc.