White Dwarfs in Ultrashort Binary Systems

TL;DR

This paper reviews the physics and emission properties of two ultrashort-period double degenerate binary systems, proposing the Unipolar Inductor Model coupled with gravitational wave emission to explain their unique observational features.

Contribution

It introduces and applies the Unipolar Inductor Model to explain the properties of the shortest orbital period binary systems, emphasizing spin-orbit coupling and GW emission effects.

Findings

Model explains main observational features of HM Cnc and V407 Vul.

Constraints on physical parameters derived for model validation.

Highlights role of spin-orbit coupling and GW emission in system dynamics.

Abstract

This contribution summarizes, as of early 2008, the observational and theoretical understanding of the physics, and emission properties of two Double Degenerate Binaries with the shortest orbital period known to date. In particular, the Unipolar Inductor Model and its coupling to GW emission have been introduced to explain a number of puzzling features that these two sources have in common and that are thought difficult to reconcile with models of mass transfer in such systems. Emphasis was put on the relevant new physical features that characterize the model. The role of spin-orbit coupling through the Lorentz torque and the role of GW emission in keeping the electric interaction active at all times has been thoroughly discussed in all their implications. Application of the model to both HM Cnc and V407 Vul accounts in a natural way for their main observational properties. Constraints on physical parameters are derived in order for the model to work, and can be verified by future observations.