Eta Scorpii

η Scorpii
Location of η Sco (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 12m 09.19565s[1]
Declination –43° 14′ 21.0905″[1]
Apparent magnitude (V) 3.33[2]
Characteristics
Spectral type F5 IV[3]
U−B color index +0.09[2]
B−V color index +0.41[2]
Astrometry
Radial velocity (Rv)–27.0[4] km/s
Proper motion (μ) RA: +24.47[1] mas/yr
Dec.: –288.55[1] mas/yr
Parallax (π)44.39 ± 0.16 mas[1]
Distance73.5 ± 0.3 ly
(22.53 ± 0.08 pc)
Absolute magnitude (MV)+1.58[5]
Details[6]
Mass1.75[7] M☉
Radius3.307±0.050 R☉
Luminosity17.94±0.45 L☉
Surface gravity (log g)3.65±0.20 cgs
Temperature6,533±46 K
Metallicity [Fe/H]−0.29±0.10 dex
Rotational velocity (v sin i)150.00 km/s
Age1.1[5] Gyr
Other designations
η Sco, CD−43 11485, FK5 638, GJ 657, HD 155203, HIP 84143, HR 6380, SAO 227707[8]
Database references
SIMBADdata

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]

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