Fast-cadence TESS Photometry and Doppler Tomography of the Asynchronous Polar CD Ind: A Revised Accretion Geometry from Newly Proposed Spin and Orbital Periods

The Transiting Exoplanet Survey Satellite observed the asynchronous polar (AP) CD Ind at a 2 min cadence almost continuously for 28 days in 2018, covering parts of five consecutive cycles of the system’s 7.3 day beat period. These observations provide the first uninterrupted photometry of a full spin-orbit beat cycle of an AP. Twice per beat cycle, the accretion flow switched between magnetic poles on the white dwarf (WD), causing the spin pulse of the WD to alternate between two waveforms after each pole switch. An analysis of the waveforms suggests that one accretion region is continuously visible when it is active, while the other region experiences lengthy self-eclipses by the WD. We argue that the previously accepted periods for both the binary orbit and the WD spin have been misidentified, and while the cause of this misidentification is a subtle and easily overlooked effect, it has profound consequences for the interpretation of the system’s accretion geometry and doubles the estimated time to resynchronization. Moreover, our timings of the photometric maxima do not agree with the quadratic ephemeris from Myers et al. and it is possible that the optical spin pulse might be an unreliable indicator of the WD’s rotation. Finally, we use Doppler tomography of archival time-resolved spectra from 2006 to study the accretion flow. While the accretion flow showed a wider azimuthal extent than is typical for synchronous polars, it was significantly less extended than in the three other APs for which Doppler tomography has been reported.