Stellar response after stripping as a model for common-envelope outcomes

Monthly Notices of the Royal Astronomical Society, vol. 511, pp. 2326–2338

Abstract

ABSTRACT Binary neutron stars have been observed as millisecond pulsars, gravitational-wave sources, and as the progenitors of short gamma-ray bursts and kilonovae. Massive stellar binaries that evolve into merging double neutron stars are believed to experience a common-envelope episode. During this episode, the envelope of a giant star engulfs the whole binary. The energy transferred from the orbit to the envelope by drag forces or from other energy sources can eject the envelope from the binary system, leading to a stripped short-period binary. In this paper, we use one-dimensional single stellar evolution to explore the final stages of the common-envelope phase in progenitors of neutron star binaries. We consider an instantaneously stripped donor star as a proxy for the common-envelope phase and study the star’s subsequent radial evolution. We determine a range of stripping boundaries that allow the star to avoid significant rapid re-expansion and that thus represent plausible boundaries for the termination of the common-envelope episode. We find that these boundaries lie above the maximum compression point, a commonly used location of the core/envelope boundary. We conclude that stars may retain fractions of a solar mass of hydrogen-rich material even after the common-envelope episode. If we consider orbital energy as the only energy source available, all of our models would overfill their Roche lobe after ejecting the envelope, whose binding energy includes gravitational, thermal, radiation, and recombination energy terms.

Authors 6

1. Alejandro Vigna-Gómez corresponding

   University of Copenhagen · ARC Centre of Excellence for Gravitational Wave Discovery · Monash University

   Affiliation as printed

   DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen, Denmark

   Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia

   Niels Bohr International Academy, The Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen, Denmark

   The ARC Center of Excellence for Gravitational Wave Discovery – OzGrav, Australia

   University of Copenhagen

2. Michelle Wassink

   Radboud University Nijmegen · Monash University

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands

   Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia

3. Jakub Klencki corresponding

   Radboud University Nijmegen

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands

4. Alina Istrate

   Radboud University Nijmegen

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands

5. Gijs Nelemans Aachen Netherlands Institute for Space Research

   Radboud University Nijmegen · Space Research Organisation Netherlands · KU Leuven

   Affiliation as printed

   Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands

   Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium

   SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, the Netherlands

6. Ilya Mandel

   ARC Centre of Excellence for Gravitational Wave Discovery · Monash University · University of Birmingham

   Affiliation as printed

   Birmingham Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK

   Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, Clayton, Victoria 3800, Australia

   The ARC Center of Excellence for Gravitational Wave Discovery – OzGrav, Australia