Possible scenarios for the formation of Ap/Bp stars |
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Authors: | A V Tutukov A V Fedorova |
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Institution: | 1.Institute of Astronomy,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | Possible paths for the formation of Ap/Bp stars—massive main-sequence stars with strong magnetic fields—are analyzed based
on modern theories for the evolution of single and binary stars. Assuming that the strong magnetic fields of these stars are
the main reason for their comparatively slow axial rotation and the observed anomalies in the chemical compositions of their
atmospheres, possible origins for these high magnetic fields are considered. Analysis of several possible scenarios for the
formation of these stars leads to the conclusion that their surface magnetic fields are probably generated in the convective
envelopes of the precursor stars. These precursors may be young, single stars with masses 1.5–3 M
⊙ that formed at the peripheries of forming star clusters and ended their accretion at the Hayashi boundary, or alternatively
close binaries whose components have convective envelopes, whose merger leads to the formation of an Ap/Bp star. Arguments
are presented supporting the view that the merger of close binaries is the main channel for the formation of Ap/Bp stars,
and a detailed analysis of this scenario is presented. The initial major axes of the merging binary systems must be in the
range 6–12 R
⊙, and the masses of their components in the range 0.7–1.5 M
⊙. When the merging components possess developed convective envelopes and fairly strong initial magnetic fields, these can
generate powerful magnetic fields “inherited” by the products of the merger—Ap/Bp stars. The reason the components of the
close binaries merge is a loss of angular momentum via the magnetic stellar winds of the components. |
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