SPH Simulations of Negative (Nodal) Superhumps: A Parametric Study

TL;DR

This study uses smoothed particle hydrodynamics simulations to analyze negative superhumps in tilted accretion discs of cataclysmic variables, exploring how system parameters influence superhump periods and revealing complex origins of the photometric signals.

Contribution

It provides the first detailed parametric simulation study of negative superhumps, including fits to superhump period deficits versus mass ratio and insights into their origins.

Findings

Negative superhumps are most prominent with an accretion stream present.

Negative superhumps can occur even without mass transfer stream, indicating complex origins.

The study offers tabulated results and fits for superhump period deficits versus mass ratio.

Abstract

Negative superhumps in cataclysmic variable systems result when the accretion disc is tilted with respect to the orbital plane. The line of nodes of the tilted disc precesses slowly in the retrograde direction, resulting in a photometric signal with a period slightly less than the orbital period. We use the method of smoothed particle hydrodynamics to simulate a series of models of differing mass ratio and effective viscosity to determine the retrograde precession period and superhump period deficit $\varepsilon_-$ as a function of system mass ratio $q$. We tabulate our results and present fits to both $\varepsilon_-$ and $\varepsilon_+$ versus $q$, as well as compare the numerical results with those compiled from the literature of negative superhump observations. One surprising is that while we find negative superhumps most clearly in simulations with an accretion stream present, we also find evidence for negative superhumps in simulations in which we shut off the mass transfer stream completely, indicating that the origin of the photometric signal is more complicated than previously believed.