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2.3 metre multi-colour photometry of a new AM Herculis variable

  • I. R. Tuohy (a1), L. Ferrario (a1), D. T. Wickramasinghe (a2) and M. R. S. Hawkins (a3)

Abstract

We present UBVRI photometry of the faint and highly erratic cataclysmic variable discovered by Hawkins (1983) from a sequence of U.K. Schmidt plates. Observations using the ANU 2.3 m telescope over two nights in September 1986 show pronounced and repeatable modulation at a binary period of 108.6 min. Dramatic colour differences are evident in the folded UBVRI light curves: in the U band, a single sinusoidal peak is present, while at longer wavelengths, a second red peak dominates at a phase separation of Δϕ = 0.5. This behaviour is strongly suggestive of cyclotron emission from two magnetic accretion funnels in an AM Herculis binary system. Furthermore, the binary period lies in the narrow range of 100-115 minutes that characterizes most of the AM Herculis variables lying on the short side of the 2-3 hour period gap. We conclude therefore that the object is almost certainly a new AM Herculis system, and develop a model in which the blue and red components originate from two non-diametrically opposed cyclotron regions that are characterized by differing electron temperatures and opacities. Predictions are made regarding the linear and circular polarization properties of this important new magnetic variable.

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2.3 metre multi-colour photometry of a new AM Herculis variable

  • I. R. Tuohy (a1), L. Ferrario (a1), D. T. Wickramasinghe (a2) and M. R. S. Hawkins (a3)

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