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arXiv · 2108.11396

Found: a rapidly spinning white dwarf in LAMOST J024048.51+195226.9

Ingrid Pelisoli·T. R. Marsh·V. S. Dhillon·E. Breedt·A. J. Brown·M. J. Dyer·M. J. Green·P. Kerry·S. P. Littlefair·S. G. Parsons·D. I. Sahman·J. F. Wild
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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 (GTC). 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% 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 24.93s, 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 0.7MSun to sustain so short a period. The observed faintest u-band magnitude sets an upper limit on the white dwarf's temperature of ~25000K. The pulsation amplitudes measured in the five HiPERCAM filters are consistent with an accretion spot of ~30000K covering ~2% of the white dwarf's visible area, although spots that are hot and smaller, or cooler and larger cannot be ruled out.

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Ingrid Pelisoli, T. R. Marsh, V. S. Dhillon, E. Breedt, A. J. Brown, M. J. Dyer, M. J. Green, P. Kerry, S. P. Littlefair, S. G. Parsons, D. I. Sahman, J. F. Wild. 2021-08-25. Found: a rapidly spinning white dwarf in LAMOST J024048.51+195226.9. https://doi.org/10.1093/mnrasl%2Fslab116

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