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Theta Eridani

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Theta Eridani
Template:Location mark
Location of θ Eridani (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
θ1 Eri
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 3.18[2]
θ2 Eri
Right ascension Template:RA[3]
Declination Template:DEC[3]
Apparent magnitude (V) 4.11[2]
Characteristics
θ1 Eri
Spectral type A3IV-V[4]
U−B Template:Engvar +0.14[5]
B−V Template:Engvar Script error: No such module "val".[6]
θ2 Eri
Spectral type A1V[4]
B−V Template:Engvar +0.08[5]
Variable type suspected[7]
Astrometry
θ1 Eri
Radial velocity (Rv)Script error: No such module "val".[6] km/s
Proper motion (μ) RA: −57.132[1] mas/yr
Dec.: +23.058[1] mas/yr
Parallax (π)19.9047±0.2062 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
θ2 Eri
Proper motion (μ) RA: −50.502[3] mas/yr
Dec.: +16.613[3] mas/yr
Parallax (π)19.5270±0.1372 mas[3]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)−0.59 (combined)[6]
Details
θ1 Eri
Mass2.6[8] Template:Solar mass
RadiusTemplate:Solar radius calculatorTemplate:Efn Template:Solar radius
Luminosity96[8] Template:Solar luminosity
Temperature8,200[8] K
Rotational velocity (v sin i)65.1[9] km/s
θ2 Eri
Mass1.95[10] Template:Solar mass
Radius2.7[11] Template:Solar radius
Luminosity37[11] Template:Solar luminosity
Surface gravity (log g)3.83[10] cgs
Temperature8,293[10] K
Metallicity [Fe/H]−0.197[10] dex
Rotational velocity (v sin i)102.5[12] km/s
Other designations
Template:Odlist
θ1 Eri: Template:Odlist
θ2 Eri: Template:Odlist
Database references
SIMBADθ1 Eri
θ2 Eri

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Theta Eridani, Latinized from θ Eridani, is a binary system in the constellation of Eridanus with a combined apparent magnitude of 2.88.[6] Its two components are designated θ1 Eridani, formally named Acamar Script error: No such module "IPAc-en". (the traditional name of the system),[13][14] and θ2 Eridani. The system's distance from the Sun based on parallax measurements is approximately 165 light-years.

Nomenclature

Theta Eridani is the system's Bayer designation; θ1 and θ2 Eridani those of its two components.

The system bore the traditional name Acamar, derived from the Arabic آخِر النَّهْر Script error: No such module "Unsubst". Ākhir an-nahr, which means "the end of the river", via a Roman-alphabet handwriting misread "rn" to "m". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[16] It approved the name "Acamar" for θ1 Eridani on 20 July 2016 and it is now so entered in the IAU Catalog of Star Names.[14]

The term "Ākhir an-nahr", or "Achr al Nahr", appeared in the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, which was translated into Latin as Postrema Fluminis.[17]

Historically, Acamar represented the end of the constellation Eridanus.[8][18] Now that distinction is held by the star Achernar, which shares the same Arabic etymology. Achernar is not visible from the Greek isles (latitudes > 33° North),[19] hence the choice of Acamar as the river's end during the time of Hipparchus and, later, Ptolemy.

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Celestial Orchard, refers to an asterism consisting of Theta Eridani, Chi Eridani, Phi Eridani, Kappa Eridani, HD 16754, HD 23319, HD 24072, HD 24160, Upsilon4 Eridani, Upsilon3 Eridani, Upsilon2 Eridani and Upsilon1 Eridani.[20] Consequently, the Chinese name for Theta Eridani itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx).[21]

Stellar system

Theta Eridani is a binary system with some evidence suggesting it is part of a multiple star system.[7][22] The main star, θ1 Eridani, is of spectral class A4 with a +3.2 apparent magnitude. Its companion star, θ2 Eridani, is of spectral class A1 with an apparent magnitude of +4.1. The angular separation of the two stars is equal to 8.3 arcseconds.[8]

Notes

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References

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  1. ↑ a b c d e Template:Cite Gaia EDR3
  2. ↑ a b Script error: No such module "Citation/CS1".
  3. ↑ a b c d e Template:Cite Gaia EDR3
  4. ↑ a b Script error: No such module "citation/CS1".
  5. ↑ a b Script error: No such module "citation/CS1".
  6. ↑ a b c d Script error: No such module "citation/CS1".
  7. ↑ a b NSV 01002, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line February 26, 2010.
  8. ↑ a b c d e Script error: No such module "citation/CS1".
  9. ↑ Script error: No such module "Citation/CS1".
  10. ↑ a b c d Script error: No such module "Citation/CS1".
  11. ↑ a b Script error: No such module "Citation/CS1".
  12. ↑ Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ a b Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "citation/CS1".
  20. ↑ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
  21. ↑ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Script error: No such module "webarchive"., Hong Kong Space Museum. Accessed on line November 23, 2010.
  22. ↑ Script error: No such module "citation/CS1".

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Template:Stars of Eridanus

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