A Transiting Planet of a Sun‐like Star

Abstract

A planet transits an 11th magnitude, G1 V star in the constellation Corona Borealis. We designate the planet XO-1b and the star XO-1, alsoknown as GSC 02041-01657. XO-1 lacks a trigonometric distance; weestimate it to be 200+/-20 pc. Of the 10 stars currently known to hostextrasolar transiting planets, the star XO-1 is the most similar to theSun in its physical characteristics: its radius is 1.0+/-0.08R solar, its mass is 1.0+/-0.03 M solar, itsVsini<3 km s -1, and its metallicity [Fe/H] is0.015+/-0.04. The orbital period of the planet XO-1b is3.941534+/-0.000027 days, one of the longer ones known. The planetarymass is 0.90+/-0.07M J, which is marginally larger than thatof other transiting planets with periods between 3 and 4 days. Both theplanetary radius and the inclination are functions of thespectroscopically determined stellar radius. If the stellar radius is1.0+/-0.08 R solar, then the planetary radius is1.30+/-0.11R J and the inclination of the orbit is87.7d+/-1.2d. We have demonstrated a productive internationalcollaboration between professional and amateur astronomers that wasimportant to distinguishing this planet from many other similarcandidates.