Rho Boötis

Rho Boötis, Latinised from ρ Boötis, is a single, orange-hued star in the northern constellation of Boötes. It is visible to the naked eye with an apparent visual magnitude of 3.59. Based upon parallax measurements, it is located at a distance of approximately 160 ly from Earth. It is moving toward the Sun with a radial velocity of −13.6 km/s. There is an optical companion, a magnitude 11.5 star, located 34.7 arcseconds away along a position angle of 345° (as of 2013).

This is an evolved K-type giant star, currently on the red-giant branch, with a stellar classification of K4 III and an estimated age of 10 billion years. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It has around 1.2 times the mass of the Sun and has expanded to 22 times the Sun's girth. The star is radiating 132 times the Sun's luminosity from its enlarged photosphere at an effective temperature of about $−13.57$. Rho Boötis is classified as a RS Canum Venaticorum variable. Koen and Eyer examined the Hipparcos data for this star, and found that it varied with a period of 5.214 days, and an amplitude of 0.0027 magnitudes.

Nomenclature
Rho Boötis is known by several different names, including ρ Boo, 25 Boötis, BD+31° 2628, FK5 534, HD 127665, HIP 71053, HR 5429, and SAO 64202. In Chinese, 梗河 (Gěng Hé), meaning Celestial Lance, refers to an asterism consisting of ρ Boötis, ε Boötis and σ Boötis. Consequently, the Chinese name for ρ Boötis itself is 梗河三 (Gěng Hé sān, the Third Star of Celestial Lance).