Eta Centauri
Star in the constellation Centaurus
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Eta Centauri is a star in the southern constellation of Centaurus. Its name is a Bayer designation that is Latinized from η Centauri, and abbreviated Eta Cen or η Cen. This star has an apparent visual magnitude of +2.35,[2] which indicates it is readily visible to the naked eye. Based on parallax measurements, it is located at a distance of around 306 light-years (94 parsecs).[1]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Centaurus |
| Right ascension | 14h 35m 30.42416s[1] |
| Declination | −42° 09′ 28.1708″[1] |
| Apparent magnitude (V) | +2.35[2] (2.30 - 2.41[3]) |
| Characteristics | |
| Spectral type | B1.5 Vne[4] |
| U−B color index | −0.862[2] |
| B−V color index | −0.215[2] |
| Variable type | GCAS[3] + LERI |
| Astrometry | |
| Radial velocity (Rv) | −0.2[5] km/s |
| Proper motion (μ) | RA: −34.73[1] mas/yr Dec.: −32.72[1] mas/yr |
| Parallax (π) | 10.67±0.21 mas[1] |
| Distance | 306 ± 6 ly (94 ± 2 pc) |
| Absolute magnitude (MV) | −2.53[6] |
| Details | |
| Mass | 12.0±0.3[7] M☉ |
| Radius | 6.10±0.12[8] R☉ |
| Luminosity | 8,700[4] L☉ |
| Surface gravity (log g) | 3.95±0.04[8] cgs |
| Temperature | 25,700[4] K |
| Rotational velocity (v sin i) | 330[4] km/s |
| Age | 5.6±1.0[7] Myr |
| Other designations | |
| η Cen, CD−41°8917, CPD−41°6839, FK5 537, HD 127972, HIP 71352, HR 5440, SAO 225044[9] | |
| Database references | |
| SIMBAD | data |
The stellar classification of this star is B1.5 Vne,[4] indicating that it is a B-type main sequence star. The 'n' suffix means that the absorption lines are broadened from rapid rotation and the 'e' that it shows emission lines in its spectrum. It has a projected rotational velocity of 330 km s−1[4] and completes a full rotation in less than a day.
As a Be star,[11] it has variable emissions in its hydrogen spectral lines. This emission can be modelled by a decretion disk of gas that has been ejected from the star by its rapid rotation and now follows a near-Keplerian orbit around the central body.[12] Its brightness is also slightly variable, and it is classified as a Gamma Cassiopeiae variable star with multiple periods of variability.[3] The International Variable Star Index lists Eta Centauri as both a Gamma Cassiopeiae variable and a Lambda Eridani variable with variations caused by its rotation and pulsations.[13]
Eta Centauri has about 12 times the mass of the Sun,[7] placing it above the dividing line between stars that evolve into white dwarfs and those that turn into supernovae. It is radiating 8,700[4] times the luminosity of the Sun from its outer atmosphere at an effective temperature of 25,700 K.[4] At this temperature, the star glows with the blue-white hue common to B-type stars.[14] Eta Centauri is a proper motion member of the Upper Centaurus–Lupus sub-group in the Scorpius–Centaurus OB association, the nearest such co-moving association of massive stars to the Sun.[15]
In traditional Chinese astronomy, Eta Centauri was known as 庫樓二[16] (meaning: the Second (Star) of Koo Low).[17]