The RR Lyrae distance to the Draco dwarf spheroidal galaxy

We present the first CCD variability study of the Draco dwarf spheroidal galaxy. The data were obtained with the Fred Lawrence Whipple Observatory 1.2 m telescope on 22 nights, over a period of 10 months, covering a 22' x 22' field centered at alpha = 17(h)19(m)57.(s)5, delta = 57degrees50'05 (J2000.0). The analysis of the BVI images produced 163 variable stars, 146 of which were RR Lyrae: 123 RRab, 16 RRc, 6 RRd, and one RR12. The other variables include a SX Phe star, four anomalous Cepheids, and a field eclipsing binary. Using the short distance scale statistical parallax calibration of Gould & Popowski and 94 RRab stars from our field, we obtain a distance modulus of (m - M)(0) = 19.40 +/- 0.02 (stat) +/- 0.15 (syst) mag for Draco, corresponding to a distance of 75.8 +/- 0.7 (stat) +/- 5.4 (syst) kpc. By comparing the spread in magnitudes of RRab stars in B, V, and I, we find no evidence for internal dust in the Draco dwarf spheroidal galaxy. The catalog of all variables, as well as their photometry and finding charts, is available electronically via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.