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Paper: The Characteristics of Magnetic CVs in the Period Gap
Volume: 315, Magnetic Cataclysmic Variables (IAU Colloquium 190)
Page: 15
Authors: Tovmassian, G.; Zharikov, S.; Mennickent, R.; Greiner, J.
Abstract: We have observed several magnetic cataclysmic variables located in the range between 2 and 3 hours, known as the period gap. This work was prompted by the recent discovery of RXJ1554.2+2721. It has 2.54 hours orbital period and shows almost pure cyclotron continuum in a low luminosity state, similar to HS1023+3900, HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to have mass transfer rates of order of a few 10-13 Solar masses/year. The aim of the study was to find out, if magnetic systems filling the period gap are in any way different from their counterparts outside that range of periods. The only significant difference we encounter is a much higher number of asynchronous magnetic systems towards longer periods than below the gap. 1. Introduction Cataclysmic Variables (CVs) are close interactive binaries with the majority of their orbital periods distributed between 80 minutes and 10 hours. The bulk of CVs (Dwarf Novae and some non-magnetic Nova-likes) show a bimodal distribution of orbital periods with a well pronounced deficiency of systems between 2 and 3 hours, known as the period gap. For a long time it's been argued and now commonly accepted that the magnetic systems does not follow that pattern and the distribution of magnetic CVs (MCVs) does not show such bi-modality (Webbink & Wickramasinghe 2002). The explanation that they suggest is based on magnetic breaking models that allow narrowing of the period gap for suffi- ciently high magnetic moment of the primary star, immediately after which the mass transfer is driven by gravitational waves. The model provides a good description of the orbital period distribution of MCVs, but it predicts much higher rates of mass transfer than has been observed in a few MCVs in the period gap and around it.
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