Document Type

Article

Publication Date

3-10-2023

Abstract

We report a peculiar variable blue star in the globular cluster (GC) NGC 6397, using Hubble Space Telescope optical imaging. Its position in the colour–magnitude diagrams and its spectrum are consistent with this star being a helium-core white dwarf (He WD) in a binary system. The optical light curve shows a periodicity at 18.5 h. We argue that this periodicity is due to the rotation of the WD and possibly due to magnetic spots on the surface of the WD. This would make this object the first candidate magnetic He WD in any GC, and the first candidate magnetic WD in a detached binary system in any GC and one of the few He WDs with a known rotation period and of magnetic nature. Another possibility is that this system is an He WD in a binary system with another WD or another degenerate object, which would make this object one of the few candidate non-accreting double-degenerate binaries in any GC.

Comments

© 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. Original published version available at https://doi.org/10.1093/mnras/stad722

Publication Title

Monthly Notices of the Royal Astronomical Society

DOI

https://doi.org/10.1093/mnras/stad722

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