The Binding Energy Parameter for Common Envelope Evolution

TL;DR

This paper systematically calculates the binding energy parameter λ for stars of 1-60 solar masses using updated stellar models, providing fitting formulas for use in population synthesis, and explores different energy contributions including enthalpy.

Contribution

It offers the first comprehensive set of λ values across a wide mass range with updated models and introduces new fitting formulas, improving common envelope evolution modeling.

Findings

Calculated λ values for 1-60 M☉ stars using updated models.

Provided fitting formulas for different λ prescriptions.

Explored enthalpy-based λ and its implications.

Abstract

The binding energy parameter $\lambda$ plays a vital role in common envelope evolution. Though it is well known that $\lambda$ takes different values for stars with different masses and varies during stellar evolution, it has been erroneously adopted as a constant in most of the population synthesis calculations. We have systematically calculated the values of $\lambda$ for stars of masses $1-60\,M_{\odot}$ by use of an updated stellar evolution code, taking into account contribution from both gravitational energy and internal energy to the binding energy of the envelope. We adopt the criterion for the core-envelope boundary advocated by \citet{Ivanova2011}. A new kind of $\lambda$ with the enthalpy prescription is also investigated. We present fitting formulae for the calculated values of various kinds of $\lambda$, which can be used in future population synthesis studies.