mass transfer. This strips the donor’s envelope and dramatically raises the mass ratio; the considered progenitor binary systems can then evolve into DWDs after passing through a single CE during the second episode of mass loss. We find that such a mechanism reproduces the properties of the observed DWD systems which have an older component with $M\lesssim 0.46\,M_\odot$ and mass ratios between the younger and older WDs of $q\ge1$.'
author:
- 'T.E. Woods'
- 'N. Ivanova'
- 'M.V. van der Sluys'
- 'S. Chaichenets'
bibliography:
- 'comenv.bib'
title: On The Formation of Double White Dwarfs Through Stable Mass Transfer and a Common Envelope
---

Introduction
============

A critical phase in the formation and evolution of most close interacting binaries is the so-called common-envelope (CE) event, during which the components of a binary system are engulfed by a common gaseous envelope. The resulting drag-like interaction will then dramatically shrink their orbit [@Os76; @Pa76]. Depending on the envelope structure and companion masses, either the envelope is ejected during this process leaving behind a close binary, or the two stars merge. Dividing the parameter space into binaries that survive CEs and those that do not, and determining the final separation for the former, 