Seginus or γ Bootis, at magnitude 3.03, is the fourth brightest star in Bootes, the Herdsman. Its name originally meant "Bootes" in Greek and was mangled in translation by the Arabs (and then re-mangled when put back to Latin). It no longer sounds anything like the original.
Properties and Evolution
At first, Seginus seems to be a typical white class A7 main-sequence star. However, unlike the class A stars of the Big Dipper, it is a giant. Class A giants are not as large as the cool K and M giants. They are just now starting to swell into their red giant phase.
From Seginus's distance of 85 light years and its surface temperature of 7600 K, we calculate a total luminosity 34 times that the Sun's, and a radius only about 3.5 times solar - hardly true "giant" size. Seginus is sill a rapid rotator, spinning at least 139 km/sec; giants slow down as they expand.
γ Boo is also a variable star, of a class known as δ Scuti. These are all stars of class A and F that vary in brightness by a few% as a result of their internal structure. Seginus' magnitude varies by around 5% over a period of about 7 hours. It is also been found to be a "non-radial" pulsator over a much shorter period, with some parts of the star moving outward while others move inward.
With a mass of around 2.5 times the Sun's, Seginus is near the end of its core hydrogen fusion. Oddly, it is surrounded by a dust small cloud, visible only in the infrared radiation; its existence is still a mystery.
Companions
Seginus has a visible 12th magnitude companion about half an arc minute away, but it is merely an optical double lying along the same the line of sight. Speckle observations, however, reveal that Seginus really does have a companion only 0.07" away, which corresponds to 1.8 AU. Nothing is known about this companion.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]