The outcomes of stellar evolution can be significantly affected by the presence of close substellar or stellar companions. Common envelopes (CE) are thought to be the main channel for producing close binaries in the universe and occur when an orbiting companion is engulfed in the outer layers of the primary’s envelope. CE outcomes are dependent on the fraction of energy from the decaying orbit that can contribute to ejecting the envelope, often defined via an efficiency, α_eff . The post-CE orbital separations and periods can then be determined given knowledge of the binding energy of the primary’s envelope. In this work, detailed stellar interior models of primaries at their maximum evolved radius are used to calculate α_eff for unique primary-companion mass pairs. Properties of the surface-contact convective region (SCCR), and its variability, are shown to affect the ejection efficiency since in these regions the energy released during inspiral can be carried to the stellar surface and radiated away. The ejection failure seen in numerical simulations may be resolved with a proper treatment of convection, whereby the binary orbit shrinks before energy can be tapped to drive ejection. With the inclusion of convection, we find post-CE orbital periods of less than a day which is an observed phenomenon infrequently achieved by population studies with a constant α_eff. A prescription for calculating α_eff given knowledge of SCCR properties is provided.

Library of Congress Subject Headings

Convection (Astrophysics)--Mathematical models; Stars--Evolution; Double stars

Publication Date


Document Type


Student Type


Degree Name

Astrophysical Sciences and Technology (MS)

Department, Program, or Center

School of Physics and Astronomy (COS)


Jason Nordhaus

Advisor/Committee Member

Joel Kastner

Advisor/Committee Member

Joshua Faber


RIT – Main Campus

Plan Codes