Found: a rapidly spinning white dwarf in LAMOST J024048.51+195226.9. Issue 1 (22nd November 2021)

• Record Type: Journal Article
• Authors: Pelisoli, Ingrid; Marsh, T R; Dhillon, V S; Breedt, E; Brown, A J; Dyer, M J; Green, M J; Kerry, P; Littlefair, S P; Parsons, S G; Sahman, D I; Wild, J F
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 509:Issue 1(2021)
• Page Start: L31
• Page End: L36
• Publication Date: 2021-11-22
• Subjects: binaries: close -- binaries: general -- stars: cataclysmic variables; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slab116
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: We present optical photometry of the cataclysmic variable LAMOST J024048.51+195226.9 taken with the high-speed, five-band CCD camera HiPERCAM on the 10.4 m Gran Telescopio Canarias . We detect pulsations originating from the spin of its white dwarf, finding a spin period of 24.9328(38) s. The pulse amplitude is of the order of 0.2 per cent in the g band, below the detection limits of previous searches. This detection establishes LAMOST J024048.51+195226.9 as only the second white dwarf magnetic propeller system, a twin of its long-known predecessor, AE Aquarii. At 24.93 s, the white dwarf in LAMOST J024048.51+195226.9 has the shortest known spin period of any cataclysmic variable star. The white dwarf must have a mass of at least 0.7 M⊙ to sustain so short a period. The observed faintest u -band magnitude sets an upper limit on the white dwarf's temperature of $\sim\!25\, 000$ K. The pulsation amplitudes measured in the five HiPERCAM filters are consistent with an accretion spot of $\sim\!30\, 000\, $ K covering ∼2 per cent of the white dwarf's visible area, although spots that are hot and smaller, or cooler and larger cannot be ruled out.