Spurious Eccentricities of Distorted Binary Components

TL;DR

This paper investigates how physical distortions in close binary stars affect their velocity curves, using observations to test theories of gravity darkening and orbital eccentricity, with implications for understanding binary star properties.

Contribution

It introduces a method to use velocity curve distortions to constrain binary system properties and tests Lucy’s gravity darkening theory with new observational data.

Findings

Detected velocity curve distortions match theoretical predictions.

Observed distortions suggest contact components are gravity darkened more than Lucy's theory predicts.

No credible evidence found for eccentric orbits in contact binary systems.

Abstract

I discuss the effect of physical distortion on the velocities of close binary components and how we may use the resulting distortion of velocity curves to constrain some properties of binary systems, such as inclination and mass ratio. Precise new velocities for 5 Cet convincingly detect these distortions with their theoretically predicted phase dependence. We can even use such distortions of velocity curves to test Lucy's theory of convective gravity darkening. The observed distortions for TT Hya and 5 Cet require the contact components of those systems to be gravity darkened, probably somewhat more than predicted by Lucy's theory but clearly not as much as expected for a radiative star. These results imply there is no credible evidence for eccentric orbits in binaries with contact components. I also present some speculative analyses of the observed properties of a binary encased in a non-rotating common envelope, if such an object could actually exist, and discuss how the limb darkening of some recently calculated model atmospheres for giant stars may bias my resuts for velocity-curve distortions, as well as other results from a wide range of analyses of binary stars.