Eta_Scorpii
Eta Scorpii, Latinized from η Scorpii, is a star in the southern zodiac constellation of Scorpius. With an apparent visual magnitude of 3.33,[2] this is one of the brighter members of the Scorpius and is the furthest south of the constellation stars with a Bayer designation.[9] The distance to this star can be estimated using parallax measurements, yielding a value of 73.5 light-years (22.5 parsecs) with a 0.4% margin of error.[1]
The stellar classification of this star has undergone some revision over time, with the star being classified anywhere from an F-type main sequence star to a giant star.[8] In 2006, the NStars program assigned it a class of F5 IV,[3] where the luminosity class of 'IV' indicates this is a subgiant star that is exhausting the supply of hydrogen at its core and is in the process of evolving into a giant star. It has around 175%[7] of the Sun's mass with an estimated age of 1.1 billion years.[5] The star is radiating about 18 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 6,533 K.[6] It is this heat that gives it a yellow-white hue that is typical for an F-type star.[10]
Eta Scorpii is rotating rapidly, with a projected rotational velocity of 150 km s−1.[7] This is causing the star to spin on its axis with a period of less than a day.[11] It is an X-ray emitter with its stellar corona giving off an X-ray luminosity of 4.4×1028 ergs s−1.[12] In 1991 it was identified as a possible barium star, as it displays an enhanced abundance of the element barium in its spectrum.[13] Overall, the abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is similar to the abundance in the Sun.[5]