Lambda Boötis

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Lambda Boötis, also named Xuange, is a bright star in the northern constellation Boötes. With a visual magnitude of about 4.18, it can be seen with the naked eye on dark nights. It lies about 100 light-years away and is moving toward us at roughly 8 km/s.

This star is a white-hued A-type main-sequence star, classified as A0p λB. It is the prototype of a rare group called Lambda Boötis stars, which have unusually low levels of heavy elements in their spectra. Lambda Boötis is about 1.7 times the Sun’s radius and 1.66 solar masses, shines about 16 times brighter, and has a surface temperature near 8900 K. It spins fairly fast, at about 100 km/s, and is about 2.8 billion years old.

Lambda Boötis is also a Delta Scuti variable, meaning its brightness changes very slightly and rapidly. Its variation has a period of about 33 minutes and an amplitude of only about 0.002 magnitudes.

There is an infrared excess around the star, which may come from a disk of dust orbiting it or from a bow wave created as the star moves through the interstellar medium.

In Chinese astronomy the star is called Xuángē, meaning “sombre lance,” and in 2017 the IAU officially approved the name Xuange for Lambda Boötis.