A candidate magnetic helium-core white dwarf in the globular cluster NGC 6397. Issue 4 (10th March 2023)

• Record Type: Journal Article
• Authors: Pichardo Marcano, Manuel; Rivera Sandoval, Liliana E; Maccarone, Thomas J; Rohrmann, Rene D; Heinke, Craig O; Belloni, Diogo; Althaus, Leandro G; Bahramian, Arash
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 4(2023)
• Page Start: 5026
• Page End: 5032
• Publication Date: 2023-03-10
• Subjects: white dwarfs -- stars: magnetic field -- globular clusters: individual: NGC 6397 -- binaries: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad722
• Languages: English
• ISSNs: 0035-8711

Abstract

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.