Magnetic accretion in SW Sextantis stars

Lima, I.J.; Rodrigues, C.V.; Szkody, P.; Lopes, C.E.; Jablonski, F.J.; Silva, K.M.; Oliveira, A.S.; Palhares, M.S.; Shugarov, S.

Авторы: Lima I.J., Rodrigues C.V., Szkody P., Lopes C.E.F, Jablonski F.J., Silva K.M.G, Oliveira A.S., Palhares M.S., Shugarov S.
Журнал: Boletín de la Asociación Argentina de Astronomía
Том: 61
Номер: 8
Год издания: 2020
Первая страница: 93
Последняя страница: 93
Аннотация: Magnetic cataclysmic variables are compact binary systems in which mass transfer occurs from a low-mass star onto a magnetic white dwarf. In polars and intermediate polars sub-classes, the magnetic field of the white dwarf is strong enough to disrupt the inner accretion disc or even completely prevent disc formation. SW Sex stars are a type of nova-like cataclysmic variables, which show observational characteristics that indicate matter outside the orbital plane is distributed asymmetrically in azimuth. Many scenarios have been proposed to explain the SW Sex behavior; one of them is magnetic accretion. In order to search for evidence of magnetic accretion in SW~Sex stars, we analyzed a set of photopolarimetric data of BO Cet, SW Sex, V442 Oph, V380 Oph, LS Peg, and UU Aqr. Polarized cyclotron emission is a distinguishing signal of magnetic accretion. If SW~Sex stars have magnetic accretion, multi-periodicity can be a typical feature of these systems as the white dwarf spins asynchronously with the orbital period. In SW~Sex, the prototype of the class, we found a period of 22.6~min in the photometry. In V442~Oph, we found a period of 12.4~min in the photometric data and its harmonics from circular and linear polarimetric data. Both systems have periods that can be related to the rotation of the magnetic white dwarfs, but a much larger data set will be needed to confirm or reject the periodicity. We found a strong peak centred at 138.2~min from a 14-year long photometric dataset of the V380~Oph. This period can be the spin period of the white dwarf, as well as the period of ∼19~min found in LS~Peg from circular polarimetric data. This period was previously reported. In BO~Cet, period analysis yields a period of 11.3~min in circular polarimetric data with the first harmonic at 22.6~min in linear polarization. In UU~Aqr, we found a period of 4.2~h from photometric data, consistent with the positive superhump.
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