Gamma Eridani

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.

γ Eridani

Location of γ Eridani (circled)
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

A light curve for Gama Eridani, plotted from Hipparcos data^[14]

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.