Epsilon Tauri
 The position of ε Tauri in the Taurus constellation. |
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| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Taurus |
| Right ascension | 04h 28m 37.00s |
| Declination | +19° 10′ 50″ |
| Apparent magnitude (V) | +3.53 |
| Characteristics | |
| Spectral type | K0III |
| B−V color index | 1.014 |
| Astrometry | |
| Proper motion (μ) |
RA: 106.19 ± 0.38 mas/yr Dec.: -37.84 ± 0.30 mas/yr |
| Parallax (π) | 22.24 ± 0.25mas |
| Distance | 147 ± 2 ly (45.0 ± 0.5 pc) |
| Absolute magnitude (MV) | 0.145 |
| Details | |
| Mass | 2.7 ± 0.1 M☉ |
| Radius | 12.692 ± 0.545 R☉ |
| Luminosity | 97 ± 8 L☉ |
| Temperature | 4901 ± 20 K |
| Metallicity [Fe/H] | +0.17 ± 0.04 dex |
| Rotational velocity (v sin i) | 3.0 km/s |
| Age | 625 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Tauri (ε Tauri, abbreviated Epsilon Tau, ε Tau), also named Ain, is an orange giant star located approximately 45 parsecs (147 light-years) from the Sun in the constellation of Taurus. An extrasolar planet (designated Epsilon Tauri b, later named Amateru) is believed to be orbiting the star.
It is a member of the Hyades open cluster. As such its age is well constrained at 625 million years. It is claimed to be the heaviest among planet-harboring stars with reliable initial masses although the star HD 13189 is potentially more massive. Given its large mass, this star, though presently of spectral type K0 III, was formerly of spectral type A that has now evolved off the main sequence into the giant phase. It is regarded as a red clump giant; that is, a core-helium burning star.
Since Epsilon Tauri lies near the plane of the ecliptic, it is sometimes occulted by the Moon and (very rarely) by planets.
It has an 11th magnitude companion 182 arcseconds from the primary.
ε Tauri (Latinised to Epsilon Tauri) is the star's Bayer designation; it also bears the Flamsteed designation of 74 Tauri. On discovery the planet was designated Epsilon Tauri b (or Ain b).
The star bore the traditional name Ain (Arabic عين for "eye") and was given the name Oculus Boreus (Latin for "Northern eye") by John Flamsteed. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Ain for this star.
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