Long-term evolution of a magnetic massive merger product

Abstract

About 10% of stars more massive than $\approx 1.5{\mathrm{M}}_{\odot }$ have strong, large-scale surface magnetic fields and are being discussed as progenitors of highly-magnetic white dwarfs and magnetars. The origin of these fields remains uncertain. Recent 3D magnetohydrodynamical simulations have shown that strong magnetic fields can be generated in the merger of two massive stars. Here, we follow the long-term evolution of such a 3D merger product in a 1D stellar evolution code. During a thermal relaxation phase after the coalescence, the merger product reaches critical surface rotation, sheds mass and then spins down primarily because of internal mass readjustments. The spin of the merger product after thermal relaxation is mainly set by the co-evolution of the star-torus structure left after coalescence. This evolution is still uncertain, so we also consider magnetic braking and other angular-momentum-gain and -loss mechanisms that may influence the final spin of the merged star. Because of core compression and mixing of carbon and nitrogen in the merger, enhanced nuclear burning drives a transient convective core that greatly contributes to the rejuvenation of the star. Once the merger product relaxed back to the main sequence, it continues its evolution similar to that of a genuine single star of comparable mass. It is a slow rotator that matches the magnetic blue straggler $\tau$ Sco. Our results show that merging is a promising mechanism to explain some magnetic massive stars and it may also be key to understand the origin of the strong magnetic fields of highly-magnetic white dwarfs and magnetars.

17 pages (incl. appendix), 14 figures, 2 tables; accepted for publication in MNRAS

References in corpus (20)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Pre-Supernova Evolution of Massive Single and Binary Stars
• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• How mergers magnetise massive stars
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: III. Angular Momentum Loss and Rotational Spindown
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• The VLT-FLAMES survey of massive stars: rotation and nitrogen enrichment as the key to understanding massive star evolution
• Luminous Blue Variables and superluminous supernovae from binary mergers
• The spectroscopic Hertzsprung-Russell diagram of Galactic massive stars
• The Triple-Ring Nebula around SN1987A: Fingerprint of a binary merger
• Magnetic field amplification and magnetically supported explosions of collapsing, non-rotating stellar cores
• The Viscous Evolution of White Dwarf Merger Remnants
• Fundamental properties of nearby single early B-type stars
• The Role of the Magnetorotational Instability in Massive Stars
• The effects of surface fossil magnetic fields on massive star evolution: II. Implementation of magnetic braking in MESA and implications for the evolution of surface rotation in OB stars
• Evidence of magnetic field decay in massive main-sequence stars
• Hydrodynamical simulations and similarity relations for eruptive mass loss from massive stars
• Super-Eddington stellar winds: unifying radiative-enthalpy vs. flux-driven models
• The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems

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• The VLT-FLAMES Tarantula Survey: Observational evidence for two distinct populations of massive runaway stars in 30 Doradus
• The effects of surface fossil magnetic fields on massive star evolution: IV. Grids of models at Solar, LMC, and SMC metallicities
• MONOS.II. Orbit review and analysis for 35 single-lined spectroscopic binary systems and candidates
• The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars
• Where are the magnetar binary companions? Candidates from a comparison with binary population synthesis predictions
• The effects of surface fossil magnetic fields on massive star evolution: III. The case of $\tau$ Sco
• The Art of Modeling Stellar Mergers and the Case of the B[e] Supergiant R4 in the Small Magellanic Cloud
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• First detection of a magnetic field in low-luminosity B[e] stars: New scenarios for the nature and evolutionary stages of FS CMa stars
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• Extreme mass ratios and fast rotation in three massive binaries
• Collision-induced mass loss and mass gain on an extremely massive star. An analytical approach and a static proto-globular cluster test-case
• The mass distribution of stellar mergers: A new scenario for several FS CMa stars
• V838 Monocerotis as seen by ALMA: a remnant of a binary merger in a triple system
• X-ray emission from candidate stellar merger remnant TYC 2597-735-1 and its Blue Ring Nebula
• Spectroscopic Line Modeling of the Fastest Rotating O-type Stars