  | |
| 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−Bcolor index | +0.09[2] |
| B−Vcolor 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 | 1.60+0.01 −0.23[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 astar in the southernzodiacconstellation ofScorpius. With anapparent visual magnitude of 3.33,[2] this is one of thebrighter members of the Scorpius and is the furthest south of the constellation stars with aBayer designation.[9] The distance to this star can be estimated usingparallax measurements, yielding a value of 73.5light-years (22.5parsecs) with a 0.4%margin of error.[1]
Thestellar classification of this star has undergone some revision over time, with the star being classified anywhere from anF-type main sequence star to agiant star.[8] In 2006, theNStars program assigned it a class of F5 IV,[3] where theluminosity class of 'IV' indicates this is asubgiant star that is exhausting the supply of hydrogen at its core and is in the process ofevolving into agiant star. It has around 1.6 times the Sun's mass[7] 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 aneffective 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 aprojected rotational velocity of150 km s−1.[11] This is causing the star to spin on its axis with a period of less than a day.[12] It is an X-ray emitter with itsstellar corona giving off an X-ray luminosity of4.4×1028 ergs s−1.[13] In 1991 it was identified as a possiblebarium star, as it displays an enhanced abundance of the element barium in itsspectrum.[14] 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]
