A Planet with a 3.1 Day Period around a Solar Twin

Abstract
Doppler measurements from the Keck/HIRES spectrometer of the G3 V star HD 187123 reveal Keplerian variations with a period of 3.097 days and a semiamplitude of 72 m s−1. An orbital fit yields a companion mass of M = 0.52 MJUP/sin i, a semimajor axis of a = 0.042 AU, and an eccentricity of e = 0.03 (consistent with zero). HD 187123 appears similar to the Sun in mass, age, chromosphere, and rotation rate. Although unlikely, non‐Keplerian explanations for the Doppler variations, such as spots and pulsation, cannot be ruled out and require future photometry and spectroscopy.