Beta Boötis, Latinized from β Boötis, and also named Nekkar,[1] is a star in the northern constellation of Boötes. It has an apparent visual magnitude of 3.5, making it one of the brighter members of the constellation. In the modern constellation, it marks the head of Boötis the herdsman. Based upon parallax measurements obtained by the Gaia spacecraft, this star is approximately 235abbr=offNaNabbr=off from the Sun. The magnitude of the star is reduced by 0.06 from extinction caused by intervening gas and dust.
β Boötis (Latinised to Beta Boötis) is the star's Bayer designation.
It bore the traditional name Nekkar or Nakkar derived from the Arabic name for the constellation: Al Baḳḳār 'the Herdsman'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name Nekkar for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[1]
An angular diameter measurement of places Nekkar's radius at . (König et al. (2006) give it 3.4 solar masses, while Tetzlaff et al. (2011) list a higher estimated mass of solar masses and Takeda et al. (2008) show it as 3.24 solar masses.) At the estimated age of, it has evolved into a giant star with a stellar classification of G8 IIIa. The star is radiating around 170–194 times as much luminosity as the Sun from its outer envelope at an effective temperature of 5,000 K. This heat gives it the yellow-hued glow of a G-type star. It has an estimated rotation period of about 200 days and the pole is inclined to the line of sight from the Earth.
In 1993, the ROSAT satellite was used to observe an X-ray flare on Beta Boötis, which released an estimated . This was the first such observation for a low-activity star of this type. The flare may be explained by an as yet unobserved M-type dwarf companion star.