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arXiv · 2410.02737

Discovery of three magnetic helium-rich hot subdwarfs with SALT

M. Dorsch·C. S. Jeffery·A. Philip Monai·C. A. Tout·E. J. Snowdon·I. Monageng·L. J. A. Scott·B. Miszalski·V. M. Woolf
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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 $T_\mathrm{eff}$ = 46500K, $\log g$ 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 $B \approx$ 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 4630\r{A} 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 4686\r{A} line to be perturbed by collisions with hydrogen atoms.

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M. Dorsch, C. S. Jeffery, A. Philip Monai, C. A. Tout, E. J. Snowdon, I. Monageng, L. J. A. Scott, B. Miszalski, V. M. Woolf. 2024-10-03. Discovery of three magnetic helium-rich hot subdwarfs with SALT. https://doi.org/10.1051/0004-6361%2F202451306

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