TESS observations of the asynchronous polar CD Ind: mapping the changing accretion geometry

Hakala, Pasi; Ramsay, Gavin; Potter, S.; Beardmore, A. P.; Buckley, D.; Wynn, G. A.

doi:10.1093/mnras/stz992

Cited by 24 publications

(26 citation statements)

References 19 publications

(40 reference statements)

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“…2) shows that the power spectrum varies cyclically at the beat period. Here again, this behavior is expected in an AP and has been observed in TESS observations of the AP CD Ind (Hakala et al 2019;Littlefield et al 2019;Mason et al 2020).…”

Section: Light Curvesupporting

confidence: 78%

Kepler K2 and TESS observations of two magnetic cataclysmic variables: The new asynchronous polar SDSS J084617.11+245344.1 and Paloma

Littlefield,

Hoard,

Garnavich

et al. 2022

Preprint

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There have been relatively few published long-duration, uninterrupted light curves of magnetic cataclysmic variable stars in which the accreting white dwarf's rotational frequency is slightly desynchronized from the binary orbital frequency (asynchronous polars). We report Kepler K2 and TESS observations of two such systems. The first, SDSS J084617.11+245344.1 was observed by the Kepler spacecraft for 80 days during Campaign 16 of the K2 mission, and we identify it as a new asynchronous polar with a likely 4.64-hour orbital period. This is significantly longer than any other asynchronous polar, as well as all but several synchronous polars. Its spin and orbital periods beat against each other to produce a conspicuous 6.77-day beat period, across which the system's accretion geometry gradually changes. The second system in this study, Paloma, was observed by TESS for one sector and was already known to be asynchronous. Until now, there had been an ambiguity in its spin period, but the TESS power spectrum pinpoints a spin period of 2.27 h. During the resulting 0.7 d spin-orbit beat period, the light curve phased on the spin modulation alternates between being singleand double-humped. We explore two possible explanations for this behavior: the accretion flow being diverted from one of the poles for part of the beat cycle, or an eclipse of the emitting region responsible for the second hump.

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Section: Light Curvesupporting

confidence: 78%

Kepler K2 and TESS observations of two magnetic cataclysmic variables: The new asynchronous polar SDSS J084617.11+245344.1 and Paloma

Littlefield,

Hoard,

Garnavich

et al. 2022

Preprint

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“…Hakala et al (2019) have independently analyzed the TESS observation and used particle-flow simulations to map the accretion geometry.3 This setting in lightkurve excludes any individual two-minute integrations whose quality flags indicate possible data-quality issues.…”

mentioning

confidence: 99%

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

Garnavich

Mukai

Mason

et al. 2019

ApJ

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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.

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“…For the actual fitting, we used a Differential Evolution (DE, Storn & Price 1997) algorithm to optimize a smoothest possible cyclotron emission map over the WD surface. This was done using a grid with 4 • resolution (see Hakala et al 2019 for more details). The fitting was carried out with fixed inclination angle.…”

Section: Sdss J22291895+1853402mentioning

confidence: 99%

Circular Polarimetry of Suspect Wind-accreting Magnetic pre-Polars

Hakala,

Parsons,

Marsh

et al. 2022

Preprint

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We present results from a circular polarimetric survey of candidate detached magnetic white dwarf -M dwarf binaries obtained using the Nordic Optical Telescope, La Palma. We obtained phase resolved spectropolarimetry and imaging polarimetry of seven systems, five of which show clearly variable circular polarisation. The data indicate that these targets have white dwarfs with magnetic field strengths > 80 MG. Our study reveals that cyclotron emission can dominate the optical luminosity at wavelengths corresponding to the cyclotron emission harmonics, even in systems where the white dwarfs are only wind-accreting. This implies that a very significant fraction of the the stellar wind of the companion star is captured by the magnetic white dwarf reducing the magnetic braking in pre-CVs. Furthermore, the polarimetric confirmation of several detached, wind-accreting magnetic systems provides observational constraints on the models of magnetic CV evolution and white dwarf magnetic field generation. We also find that the white dwarf magnetic field configuration in at least two of these systems appears to be very complex.

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TESS observations of the asynchronous polar CD Ind: mapping the changing accretion geometry

Cited by 24 publications

References 19 publications

Kepler K2 and TESS observations of two magnetic cataclysmic variables: The new asynchronous polar SDSS J084617.11+245344.1 and Paloma

Kepler K2 and TESS observations of two magnetic cataclysmic variables: The new asynchronous polar SDSS J084617.11+245344.1 and Paloma

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

Circular Polarimetry of Suspect Wind-accreting Magnetic pre-Polars

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