Possible pair-instability supernovae at solar metallicity from magnetic stellar progenitors

¹ Geneva Observatory, University of Geneva, Maillettes 51, 1290 Sauverny, Switzerland
e-mail: cyril.georgy@unige.ch
² Department of Physics, Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON K7K 0C6, Canada
³ Department of Physics and Space Sciences, Florida Institute of Technology, 150 W. University Blvd, Melbourne, FL 32904, USA
⁴ Department of Physics, Engineering Physics and Astronomy, Queen’s University, 99 University Avenue, Kingston, ON K7L 3N6, Canada
⁵ Astrophysics group, Keele University, Keele, Staffordshire ST5 5BG, UK
⁶ Kavli IPMU (WPI), Tokyo Institutes for Advanced Study, The University of Tokyo, 5-1-5 Kashiwanoha, Chiba 277-8583, Japan

Received: 5 January 2017
Accepted: 7 February 2017

Abstract

Near-solar metallicity (and low-redshift) pair-instability supernova (PISN) candidates challenge stellar evolution models. Indeed, at such a metallicity, even an initially very massive star generally loses so much mass by stellar winds that it will avoid the electron-positron pair-creation instability. We use recent results showing that a magnetic field at the surface of a massive star can significantly reduce its effective mass-loss rate to compute magnetic models of very massive stars (VMSs) at solar metallicity and explore the possibility that such stars end as PISNe. We implement the quenching of the mass loss produced by a surface dipolar magnetic field into the Geneva stellar evolution code and compute new stellar models with an initial mass of 200 M_⊙ at solar metallicity, with and without rotation. This considerably reduces the total amount of mass lost by the star during its life. For the non-rotating model, the total (CO-core) mass of the models is 72.8 M_⊙ (70.1 M_⊙) at the onset of the electron-positron pair-creation instability. For the rotating model, we obtain 65.6 M_⊙ (62.4 M_⊙). In both cases, a significant fraction of the internal mass lies in the region where pair instability occurs in the log (T)−log (ρ) plane. The interaction of the reduced mass loss with the magnetic field efficiently brakes the surface of the rotating model, producing a strong shear and hence a very efficient mixing that makes the star evolve nearly homogeneously. The core characteristics of our models indicate that solar metallicity models of magnetic VMSs may evolve to PISNe (and pulsation PISNe).