Multicolor Observations of a Planetary Transit of Hd 209458

We present BV RIZ photometric observations of HD 209458 during the transit by its planetary companion on UT 1999 November 15 with the University of Hawaii 0.6m and 2.2m telescopes and the High Altitude Observatory STARE telescope. The detailed shape of the transit curve is predicted to vary with color due primarily to the color-dependent limb-darkening of the star, but potentially due as well to the effect of color-dependent opacity in the planetary atmosphere. We model the light curves and present refined values for the transit timing and orbital period, useful for planning future observations of the planetary transit. We also derive significantly improved measurements of the planetary radius, Rp = 1.55± 0.10RJup, stellar radius, Rs = 1.27± 0.05R⊙, and orbital inclination, i = 85.9± 0.5 . The derived planetary radius favors evolutionary models in which the planet has a low albedo. Subject headings: binaries: eclipsing — planetary systems — stars: individual (HD 209458) — techniques: photometric