TESS photometry of the asynchronous polar CD Ind: A short period analog of BY Cam

Mason, P.A.; Morales, J.F.; Littlefield, C.; Garnavich, P.; Pavlenko, E.P.; Szkody, P.; Kennedy, M.; Myers, G.; Schwarz, R.; Babina, J.V.; Sosnovskij, A.A.; Antonyuk, O.I.; Shugarov, S.Y.; Andreev, M.V.

Авторы: Mason Paul A., Morales John F., Littlefield Colin, Garnavich Peter, Pavlenko Elena P., Szkody Paula, Kennedy Mark, Myers Gordon, Schwarz Robert, Babina Julia V., Sosnovskij Alexsei A., Antonyuk Oksana I., Shugarov Sergey Yu, Andreev Maksim V.
Журнал: Advances in Space Research
Том: 66
Номер: 5
Год издания: 2020
Издательство: Pergamon Press Ltd.
Местоположение издательства: United Kingdom
Первая страница: 1123
Последняя страница: 1138
DOI: 10.1016/j.asr.2020.03.038
Аннотация: We present a time-series analysis of the asynchronous polar CD Ind, using fast cadence TESS photometry. A similar analysis is performedusing ground based photometry of BY Cam. These asynchronous polars show remarkably similar light curves and enigmatictiming characteristics. A pair of competing models for the assignment of the white dwarf spin period have been presented for both binaries.TESS allows for the breaking of this degeneracy by providing continuous coverage over several beat-cycles. The CD Ind light curvedisplays a super-orbital period of 7.2 days due to beat-phased modulation of the accretion rate onto a permanently visible spot. This(main) accretion region is active for 3/4 of the beat-cycle. The dominant photometric signal is at 109.654(4) min and is identified as aside-band related to the white dwarf spin and the binary orbit, analogous to that found in BY Cam. We obtain the white dwarf spinperiod of CD Ind as 110.820(5) min and an orbital period of 111.952(8) min. The TESS light curve supports a pole-switching scenariofor CD Ind, with a total of 4 alternating, and oppositely positioned accretion regions. This inclination of CD Ind is estimated asi = 65^o +\- 10^o. One accretion region remains in view of the observer at all times. In addition, two pulsed accretion spots each accretefor just less than 1/2 of the beat-cycle. These alternating spots are orthogonal to the main accretion region (which is always in view),and are found to be roughly 180^o apart in longitude. Finally, since the mean flux drops by a factor of 2 for about 1/4 of the beatcycleand the dominant accretion region turns off during this time, we hypothesize the existence of a fourth (permanently hidden) accretionregion opposite to the one permanently in view. Photometric models for the 2- and 4-pole accretion configurations are developedand only the 4-pole model is consistent with the observed periodogram for CD Ind. We conclude that complex magnetic fields affect accretion flow onto these white dwarf stars. In particular, the magnetic field of the white dwarf in both of these binaries is inconsistentwith either a centered or an offset dipole configuration.
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TESS photometry of the asynchronous polar CD Ind: A short period analog of BY Camстатья

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