Xi Boötis
Template:Short description Template:Starbox begin Template:Starbox image Template:Starbox observe Template:Starbox character Template:Starbox astrometry Template:Starbox visbin Template:Starbox detail Template:Starbox catalog Template:Starbox reference Template:Starbox end
Xi Boötis is a binary star<ref name=aaa338_455/> system in the northern constellation of Boötes. Its name is a Bayer designation that is Latinised from ξ Boötis, and abbreviated Xi Boo or ξ Boo. This is the nearest visible star in the constellation Boötes. The brighter, primary component of the pair has a typical apparent visual magnitude of 4.70, making it visible to the naked eye. Based on parallax measurements, it is located at a distance of Template:Convert from Earth. The pair are drifting further from the Sun with a radial velocity of +2 km/s.<ref name=GaiaDR3a/>
Properties
The primary star in this system is a G-type main-sequence star with a stellar classification of G8 Ve,<ref name=Levato_Abt_1978/> where the 'e' notation indicates emission lines in the spectrum. It is a BY Draconis variable with an apparent magnitude that varies from +4.52 to +4.67 with a period just over 10 days long. The magnetic activity in the star's chromosphere varies with time, but no activity cycle has been found (as of 2019).<ref name=Finley_et_al_2019/> It has 88% of the mass and 82% of the radius of the Sun, but shines with just 56% the Sun's luminosity.<ref name=Karovicova/>
The secondary component is a smaller K-type main-sequence star with a class of K4 Ve.<ref name=Levato_Abt_1978/> It has 66% of the Sun's mass and 61% of the Sun's radius. The star is radiating just 6.1% of the luminosity of the Sun from its photosphere at an effective temperature of 4,350 K.<ref name=aaa338_455/> This gives it an apparent visual magnitude of 6.8,<ref name="Høg_et_al_2000"/> which by itself would be a challenge to view with the naked eye. As of 2019, it is located at an angular separation of Template:Val from the primary, along a position angle of 298°.<ref name=Mason_et_al_2014/>
The pair follow a wide, highly elliptical orbit around their common barycenter, completing an orbit every 152.5 years.<ref name=Izmailov2025/> Radial velocity measurements taken of the primary as part of an extrasolar planet search show a linear trend in the velocities that is likely due to the secondary star.<ref name="Howard2016"/> The pair can be resolved using a small telescope. The binary system contains two of the closest young solar-type stars to the Sun, with a system age of about 200 million years old.<ref name=apj687_2_1264/>
The primary star, component A, has been identified as a candidate for possessing a Kuiper-like belt,<ref name=hinshaw19970203/> based on infrared observations. The estimated minimum mass of this dust disk is 2.4 times the mass of the Earth's Moon. (Compare to the value of 8.2 lunar masses for the Kuiper belt.)<ref name=aj125_6_3334/>
A necessary condition for the existence of a planet in this system are stable zones where the object can remain in orbit for long intervals. For hypothetical planets in a circular orbit around the individual members of this star system, this maximum orbital radius is computed to be Template:Val for the primary and 3.5 AU for the secondary. A planet orbiting outside of both stars would need to be at least 108 AU distant.<ref name=mnras427_4_2723/>