THE ECLIPSING AM HERCULIS VARIABLE H1907+690

We report the discovery of an eclipsing cataclysmic variable that exhibits up to 10% circular polarization at optical wavelengths, securing its classification as an AM Herculis type binary. The object, H1907 + 690, was located with the guidance of X-ray positions from the HEAO 1 survey. Optical CCD photometry exhibits deep eclipses, from which we derive a precise orbital period of 1.743750 hr. The eclipse duration suggests an inclination angle approximately 80-degrees for a main-sequence secondary star. The optical flux has been persistently faint (V approximately 18) during observations spanning 1987-1990, while the X-ray measurements (one decade earlier) suggest long-term X-ray variability. The polarization and photometric light curves can be interpreted with a geometric model in which most of the accretion is directed toward a single magnetic pole, with an accretion spot displaced approximately 17-degrees in longitude from the projection of the secondary star on the white dwarf surface. The light curves also indicate that the accreting pole passes behind the white dwarf for 0.32 of the spin period, leading to an estimate of 18-degrees for the colatitude of the accretion spot, relative to the spin axis of the white dwarf. The 3 year stability of the photometric light curve, relative to the eclipse ephemeris, implies spin-orbital synchrony with DELTA-P/P < 10(-5) (3-sigma). Substantial optical flux is observed while the accreting pole is behind the white dwarf, but the origin of this unpolarized continuum remains ambiguous.