| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 17h12m 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] |
| Distance | 73.5 ± 0.3 ly (22.53 ± 0.08 pc) |
| Absolute magnitude (MV) | +1.58[5] |
| Details[6] | |
| Mass | 1.75[7] M☉ |
| Radius | 3.307±0.050 R☉ |
| Luminosity | 17.94±0.45 L☉ |
| Surface gravity (log g) | 3.65±0.20 cgs |
| Temperature | 6,533±46 K |
| Metallicity [Fe/H] | −0.29±0.10 dex |
| Rotational velocity (v sin i) | 150.00 km/s |
| Age | 1.1[5] Gyr |
| Other designations | |
η Sco, CD−43 11485, FK5 638, GJ 657, HD 155203, HIP 84143, HR 6380, SAO 227707[8] | |
| Database references | |
| SIMBAD | data |
Eta Scorpii, Latinized from η Scorpii, is a star in the southern zodiac constellationofScorpius. 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 velocityof150 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]
