A Transiting Planet of a Sun-like Star

A planet transits an 11 magnitude, G1V star in the constellation Corona Borealis. We designate the planet XO-1b, and the star, XO-1, also known as GSC 02041-01657. XO-1 lacks a trigonometric distance; we estimate it to be 200±20 pc. Of the ten stars currently known to host extrasolar transiting planets, the star XO-1 is the most similar to the Sun in its physical characteristics: its radius is 1.0±0.08 R⊙, its mass is 1.0±0.03 M⊙, V sini < 3 km s, and its metallicity [Fe/H] is 0.015±0.04. The orbital period of the planet XO-1b is 3.941534±0.000027 days, one of the longer ones known. The planetary mass is 0.90±0.07 MJ, which is marginally larger than that of other transiting planets with periods between 3 and 4 days. Both the planetary radius and the inclination are functions of the spectroscopically determined stellar radius. If the stellar radius is 1.0±0.08 R⊙, then the planetary radius is 1.30±0.11 RJ and the inclination of the orbit is 87.7±1.2. We have demonstrated a productive international Space Telescope Science Institute, 3700 San Martin Dr., Baltimore MD 21218 University of Illinois, Urbana, IL 61801 Dept. of Physics and Astronomy, Rice University, 6100 Main Street, MS-108, Houston, TX 77005 Visiting Astronomer, McDonald Observatory, which is operated by the University of Texas at Austin. Boston University, Astronomy Dept., 725 Commonwealth Ave., Boston, MA 02215 University of Hawaii, Inst. for Astronomy, 2680 Woodlawn Dr., Honolulu, HI 96822-1839 Dept. of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 Racoon Run Observatory, Pleasanton, CA Hereford Arizona Observatory, 5320 E. Calle Manzana, Hereford, AZ 85615 CBA Belgium Observatory, Walhostraat 1A, B-3401 Landen, Belgium