Confirmation of a Second Propeller: A High-Inclination Twin of AE~Aquarii

Abstract

For decades, AE Aquarii (AE Aqr) has been the only cataclysmic variable star known to contain a magnetic propeller: a persistent outflow whose expulsion from the binary is powered by the spin-down of the rapidly rotating, magnetized white dwarf. In 2020, LAMOST-J024048.51+195226.9 (J0240) was identified as a candidate eclipsing AE Aqr object, and we present three epochs of time-series spectroscopy that strongly support this hypothesis. We show that during the photometric flares noted by Thorstensen (2020) (arXiv:2007.09285), the half-width-at-zero-intensity of the Balmer and HeI lines routinely reaches a maximum of ~3000 km/s, well in excess of what is observed in normal cataclysmic variables. This is, however, consistent with the high-velocity emission seen in flares from AE Aqr. Additionally, we confirm beyond doubt that J0240 is a deeply eclipsing system. The flaring continuum, HeI and much of the Balmer emission likely originate close to the WD because they disappear during the eclipse that is centered on inferior conjunction of the secondary star. The fraction of the Balmer emission remaining visible during eclipse has a steep decrement and it is likely produced in the extended outflow. Most enticingly of all, this outflow produces a narrow P-Cyg absorption component for nearly half of the orbit, and we demonstrate that this scenario closely matches the outflow kinematics predicted by Wynn, King, & Horne (1997). While an important piece of evidence for the magnetic-propeller hypothesis -- a rapid WD spin period -- remains elusive, our spectra provide compelling support for the existence of a propeller-driven outflow viewed nearly edge-on, enabling a new means of rigorously testing theories of the propeller phenomenon.

14 pages, 11 figures, accepted for publication in the Astrophysical Journal

References in corpus (9)

• Evolutionary Stellar Population Synthesis with MILES. Part I: The Base Models and a New Line Index System
• The Catalina Surveys Periodic Variable Star Catalog
• A radio pulsing white dwarf binary star
• V1460 Her: A fast spinning white dwarf accreting from an evolved donor star
• CTCV J2056-3014: An X-ray-faint Intermediate Polar Harboring An Extremely Fast-spinning White Dwarf
• High Dispersion Absorption-line Spectroscopy of AE Aqr
• Follow-up Studies of Five Cataclysmic Variable Candidates Discovered by LAMOST
• Driving the Beat: Time-Resolved Spectra of the White Dwarf Pulsar AR Scorpii
• Radio and optical observations of the possible AE Aqr twin, LAMOST J024048.51+195226.9

Cited by in corpus (9)

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• Radio detections of two unusual cataclysmic variables in the VLA Sky Survey
• Optical detection of the rapidly spinning white dwarf in V1460 Her
• Searching for cataclysmic variable stars in unidentified X-ray sources
• VLA Observations of the AE Aqr-type Cataclysmic Variable LAMOST J024048.51+195226.9
• VLBI detection of the AE Aqr twin, LAMOST J024048.51+195226.9
• Exploration of faint X-ray and radio sources in the massive globular cluster M14: A UV-bright counterpart to Nova Ophiuchus 1938
• X-ray emission mechanisms in accreting white dwarfs