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

Abstract

The TESS spacecraft observed the asynchronous polar CD Ind at a two-minute cadence almost continuously for 28 days in 2018, covering parts of 5 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 asynchronous polar. Twice per beat cycle, the accretion flow switched between magnetic poles on the white dwarf, causing the spin pulse of the white dwarf (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 white dwarf. 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. (2017), and it is possible that the optical spin pulse might be an unreliable indicator of the white dwarf'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 asynchronous polars for which Doppler tomography has been reported.

Accepted for publication in ApJ. For an independent analysis of the TESS light curve of CD Ind, see Hakala et al. 2019, MNRAS, 486, 2549

References in corpus (11)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• The Transiting Exoplanet Survey Satellite
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• IGR J19552+0044: A new asynchronous short period polar: "Filling the gap between intermediate and ordinary polars"
• Exploring inside-out Doppler tomography: magnetic cataclysmic variables
• Resynchronization of the Asynchronous Polar CD Ind
• TESS observations of the asynchronous polar CD Ind: mapping the changing accretion geometry
• Asynchronous polar V1500 Cyg: orbital, spin and beat periods

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• Study of Complex Absorption and Reflection in a Unique Intermediate Polar Paloma
• A systematic search for orbital periods of polars with TESS. Methods, detection limits, and results
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• Revisiting the X-ray Emission of the Asynchronous Polar V1432 Aql