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The Orbital Period and Variability of the Dwarf Nova ES Draconis

A radial velocity study of the cataclysmic variable ES Dra (PG 1524+622) is presented. ES Dra is found to have an orbital period of 0.17660 \pm 0.00006 d (4.2384 \pm 0.0014 h). The mass-losing secondary star of ES Dra is detectable in the spectrum, and it has a spectral type of M2 \pm 1. From this, we estimate the absolute magnitude of ES Dra during our spectroscopic observations to have been MR = 6.5 \pm 0.5, and its distance to be 720 \pm 150 pc. The long-term light curve of ES Dra compiled by the American Association of Variable Star Observers (AAVSO) shows that ES Dra is a Z Cam star, which between 1995 and 2009 spent most of its time in standstill.