Eta Scorpii
Binary star in the constellation Scorpius
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Characteristics
The two components of this system are separated by 9.87" in the sky, and were identified as a gravitationally bound pair in 2018 with data from the Gaia spacecraft.
The stellar classification of the primary star, Eta Scorpii A, has undergone some revision over time, with the star being classified anywhere from an F-type main sequence star to a giant star. In 2006, the NStars program assigned it a class of F5 IV, 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 1.6 times the Sun's mass with an estimated age of 1.1 billion years. The star is radiating about 18 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 6,533 K. It is this heat that gives it a yellow-white hue that is typical for an F-type star.
Eta Scorpii A is rotating rapidly, with a projected rotational velocity of 150 km s−1. This is causing the star to spin on its axis with a period of less than a day. It is an X-ray emitter with its stellar corona giving off an X-ray luminosity of 4.4×1028 ergs s−1. In 1991 it was identified as a possible barium star, as it displays an enhanced abundance of the element barium in its spectrum. 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.
The secondary component, Eta Scorpii B, also designated L 413-148, has a much fainter apparent magnitude of +11.23. It has no published spectral type. The star has roughly 0.53 times the mass of the Sun and 0.52 times the radius. It is radiating about 5% of the Sun's luminosity at an effective temperature of approximately 3,600 K.