Convection and Spin-Up During Common Envelope Evolution: The Formation of Short-Period Double White Dwarfs

TL;DR

This paper investigates how convective effects influence the common envelope phase in binary star systems, specifically affecting the formation and characteristics of short-period double white dwarfs, which are important for gravitational wave sources and supernovae.

Contribution

It introduces a detailed model including convection and spin-up effects in common envelope evolution, improving predictions of double white dwarf populations.

Findings

Predicted post-CE separations match observed DWD orbital parameters.

Convection plays a crucial role in energy accommodation during envelope ejection.

Model supports convection as a key factor in common envelope evolution.

Abstract

The formation channels and predicted populations of double-white dwarfs (DWDs) are important because a subset will evolve to be gravitational-wave sources and/or progenitors of Type Ia supernovae. Given the observed population of short-period DWDs, we calculate the outcomes of common envelope evolution when convective effects are included. For each observed white dwarf in a DWD system, we identify all progenitor stars with an equivalent proto-WD core mass from a comprehensive suite of stellar evolution models. With the second observed white dwarf as the companion, we calculate the conditions under which convection can accommodate the energy released as the orbit decays, including (if necessary), how much the envelope must spin-up during the common envelope phase. The predicted post-CE final separations closely track the observed DWD orbital parameter space, further strengthening the view that convection is a key ingredient in common envelope evolution.