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AM Herculis(her-kyŭ-liss) The archetypal magnetic white dwarf binary system, or polar, identified in 1976 from an Uhuru X-ray source. Optically it is a faint variable binary star (mag. 12–15), exhibiting strong optical polarization and a photometric period of 185 minutes. X-ray emission is strongly modulated at the same period, due to rotation of the white dwarf. The characteristic high XUV-to-optical luminosity ratio has led to several other similar systems being found from X-ray and XUV surveys. See magnetic cataclysmic variables.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006