Discovery of three magnetic helium-rich hot subdwarfs with SALT
arXiv:2410.02737 · doi:10.1051/0004-6361/202451306
Abstract
Magnetic fields with strengths ranging from 300 to 500 kG have recently been discovered in a group of four extremely similar helium-enriched hot subdwarf (He-sdO) stars. Besides their strong magnetic fields, these He-sdO stars are characterised by common atmospheric parameters, clustering around = 46500K, close to 6, and intermediate helium abundances. Here we present the discovery of three additional magnetic hot subdwarfs, J123359.44-674929.11, J125611.42-575333.45, and J144405.79-674400.93. These stars are again almost identical in terms of atmospheric parameters but, at 200kG, their magnetic fields are somewhat weaker than those previously known. The close similarity of all known He-sdOs implies a finely-tuned origin. We propose the merging of an He white dwarf with a H+He white dwarf. A differential rotation at the merge interface may initiate a toroidal magnetic field that evolves by a magnetic dynamo to produce a poloidal field. This field is either directly visible at the surface or may diffuse towards the surface if initially buried. We further discuss a broad absorption line centred at about 4630Å that is common to all magnetic He-sdOs. This feature may not be related to the magnetic field but instead to the intermediate helium abundances in these He-sdO stars, allowing the strong He II 4686Å line to be perturbed by collisions with hydrogen atoms.
arXiv commentAccepted for publication in A&A. The figures in the appendix will only be linked to zenodo in the A&A version, but are properly included here
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