Gamma Eridani
Variable star in the constellation Eridanus
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Gamma Eridani (γ Eridani, abbreviated Gamma Eri, γ Eri), formally named Zaurak /ˈzɔːræk/,[12][13] is a variable star in the constellation of Eridanus. It is visible to the naked eye with an apparent visual magnitude that varies around 2.9, and lies at a distance of about 203 light years from the Sun, as determined by the Hipparcos astrometry satellite.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Eridanus |
| Right ascension | 03h 58m 01.76695s[1] |
| Declination | −13° 30′ 30.6698″[1] |
| Apparent magnitude (V) | 2.88 - 2.96[2] |
| Characteristics | |
| Evolutionary stage | AGB[3] |
| Spectral type | M0III-IIIb[4] |
| U−B color index | +1.96[5] |
| B−V color index | +1.58[5] |
| Variable type | Lb?[2] |
| Astrometry | |
| Radial velocity (Rv) | 60.81±0.25[6] km/s |
| Proper motion (μ) | RA: +61.57[1] mas/yr Dec.: −113.11[1] mas/yr |
| Parallax (π) | 17.0016±0.2254 mas[7] |
| Distance | 192 ± 3 ly (58.8 ± 0.8 pc) |
| Absolute magnitude (MV) | −1.19[8] |
| Details | |
| Mass | 1.55[9] M☉ |
| Radius | 58.7±0.8[10] R☉ |
| Luminosity | 634.2±28.6[10] L☉ |
| Surface gravity (log g) | 1.52[10] cgs |
| Temperature | 3,779±34[10] K |
| Metallicity [Fe/H] | +0.00[10] dex |
| Rotational velocity (v sin i) | 3.8[6] km/s |
| Other designations | |
| Zaurak, γ Eri, 34 Eri, BD−13 781, HD 25025, HIP 18543, HR 1231, SAO 149283[11] | |
| Database references | |
| SIMBAD | data |
Description
Gamma Eridani has been defined as a standard star for the spectral class M0III-IIIb.[4] It is a red giant on the asymptotic giant branch, fusing hydrogen and helium in separate shells outside its core.[3] Observations published in 1960 showed it to vary in brightness by a few hundredths of a magnitude.[15] In 1977, it was officially listed as a variable star in the General Catalogue of Variable Stars although the class of variable is uncertain.[16]
The Gaia EDR3 data identified a comoving 0.1 M☉ companion star of Gamma Eridani, at a projected separation of 1000 AU. It is likely that there is an additional red dwarf companion that at a distance within 50 AU, too close to resolve from the primary.[17]
Nomenclature
Gamma Eridani is the star's Bayer designation. It has the traditional name Zaurak, alternatively spelled Zaurac, which is one of the Arabic words for 'boat'.[18] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[19] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[20] included a table of the first two batches of names approved by the WGSN; which included Zaurak for this star.
In Chinese, 天苑 (Tiān Yuàn), meaning Celestial Meadows, refers to an asterism consisting of γ Eridani, δ Eridani, π Eridani, ε Eridani, ζ Eridani, η Eridani, π Ceti, τ1 Eridani, τ2 Eridani, τ3 Eridani, τ4 Eridani, τ5 Eridani, τ6 Eridani, τ7 Eridani, τ8 Eridani and τ9 Eridani.[21] Consequently, the Chinese name for γ Eridani itself is 天苑一 (Tiān Yuàn yī, English: the First [Star] of Celestial Meadows.)[22]
USS Zaurak (AK-117) was a United States Navy Crater class cargo ship named after the star.