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Theta Eridani
	Location of θ Eridani (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Eridanus
	θ1 Eri
Right ascension	02h 58m 15.6764s
Declination	−40° 18′ 16.839″
Apparent magnitude (V)	3.18
	θ2 Eri
Right ascension	02h 58m 16.4037s
Declination	−40° 18′ 16.906″
Apparent magnitude (V)	4.11
Characteristics
θ1 Eri
Spectral type	A3IV-V
U−B color index	+0.14
B−V color index	+0.128±0.012
θ2 Eri
Spectral type	A1V
B−V color index	+0.08
Variable type	suspected
Astrometry
θ1 Eri
Radial velocity (Rv)	+11.9±2.6 km/s
Proper motion (μ)	RA: −57.132 mas/yr ; Dec.: +23.058 mas/yr
Parallax (π)	19.9047 ± 0.2062 mas
Distance	164 ± 2 ly ; (50.2 ± 0.5 pc)
θ2 Eri
Proper motion (μ)	RA: −50.502 mas/yr ; Dec.: +16.613 mas/yr
Parallax (π)	19.5270 ± 0.1372 mas
Distance	167 ± 1 ly ; (51.2 ± 0.4 pc)
Absolute magnitude (MV)	−0.59 (combined)
Details
θ1 Eri
Mass	2.6 M☉
Radius	4.85 R☉
Luminosity	96 L☉
Temperature	8,200 K
Rotational velocity (v sin i)	65.1 km/s
θ2 Eri
Mass	1.95 M☉
Radius	2.7 R☉
Luminosity	37 L☉
Surface gravity (log g)	3.83 cgs
Temperature	8,293 K
Metallicity [Fe/H]	−0.197 dex
Rotational velocity (v sin i)	102.5 km/s
Other designations
	Theta Eri, θ Eri, CD−40° 771, HIP 13847, SAO 216113, CCDM J02583-4018, WDS 02583-4018
	θ1 Eri: Acamar, HD 18622, HR 897
	θ2 Eri: HD 18623, HR 898
Database references
SIMBAD	θ1 Eri
	θ2 Eri

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 /ˈækəmɑːr/ (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 ^{[citation needed]} 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, 天園 (Tiān Yuán), 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 天園六 (Tiān Yuán liù, English: the Sixth Star of Celestial Orchard).^[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

^ Retrieved from a luminosity of 96 L_☉ and a temperature of 8200 K^[8]

References

^ ^a ^b ^c ^d ^e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
^ ^a ^b Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (1 March 2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822. ISSN 0004-6361.
^ ^a ^b ^c ^d ^e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
^ ^a ^b Gray, R. O.; et al. (2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
^ ^a ^b Hoffleit; et al. (1991). "Bright Star Catalogue". VizieR (5th Revised ed.). Centre de Données astronomiques de Strasbourg. Retrieved 2010-02-24.
^ ^a ^b ^c ^d Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ ^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.
^ ^a ^b ^c ^d ^e ^f Kaler, James B. "ACAMAR (Theta Eridani)". Stars. University of Illinois. Retrieved 2010-02-24.
^ Ammler-von Eiff, M.; Reiners, A. (June 2012). "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?". Astronomy & Astrophysics. 542: A116. arXiv:1204.2459. Bibcode:2012A&A...542A.116A. doi:10.1051/0004-6361/201118724. ISSN 0004-6361.
^ ^a ^b ^c ^d Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; de Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy & Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361.
^ ^a ^b Stassun, Keivan G.; et al. (2019-10-01). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. hdl:1721.1/124721. ISSN 0004-6256. S2CID 166227927.
^ Díaz, C. G.; et al. (July 2011). "Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum". Astronomy & Astrophysics. 531: A143. arXiv:1012.4858. Bibcode:2011A&A...531A.143D. doi:10.1051/0004-6361/201016386. S2CID 119286673.
^ Rumrill, H. B. (June 1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. 48 (283). San Francisco, California: 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681. S2CID 120743052.
^ ^a ^b "IAU Catalog of Star Names". Retrieved 28 July 2016.
^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55: 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
^ Rogers, J. H. (1998). "Origins of the ancient constellations: II. The Mediterranean traditions". Journal of the British Astronomical Association. 108 (2): 79–89. Bibcode:1998JBAA..108...79R.
^ Larry Sessions. "Achernar: End of the River". EarthSky Tonight Post 06-29-2009. Retrieved 2010-02-26.
^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-09-03 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
^ "Acamar". Alcyone Bright Star Catalogue. Retrieved 2010-02-26.

[Temperature_and_luminosity-9] Retrieved from a luminosity of 96 L_☉ and a temperature of 8200 K^[8]

[edr3a-1] Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.

[tycho2-2] Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (1 March 2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822. ISSN 0004-6361.

[edr3b-3] Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.

[Gray_et_al_2006-4] Gray, R. O.; et al. (2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.

[VizieR-5] Hoffleit; et al. (1991). "Bright Star Catalogue". VizieR (5th Revised ed.). Centre de Données astronomiques de Strasbourg. Retrieved 2010-02-24.

[Anderson2012-6] Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.

[nsv1-7] NSV 01002, database entry, New Catalogue of Suspected Variable Stars, the improved version, Sternberg Astronomical Institute, Moscow, Russia. Accessed on line February 26, 2010.

[kaler-8] ^ ^a ^b ^c ^d ^e ^f Kaler, James B. "ACAMAR (Theta Eridani)". Stars. University of Illinois. Retrieved 2010-02-24.

[ammler2012-10] Ammler-von Eiff, M.; Reiners, A. (June 2012). "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?". Astronomy & Astrophysics. 542: A116. arXiv:1204.2459. Bibcode:2012A&A...542A.116A. doi:10.1051/0004-6361/201118724. ISSN 0004-6361.

[starhorse-11] Anders, F.; Khalatyan, A.; Chiappini, C.; Queiroz, A. B.; Santiago, B. X.; Jordi, C.; Girardi, L.; Brown, A. G. A.; Matijevič, G.; Monari, G.; Cantat-Gaudin, T.; Weiler, M.; Khan, S.; Miglio, A.; Carrillo, I.; Romero-Gómez, M.; Minchev, I.; de Jong, R. S.; Antoja, T.; Ramos, P.; Steinmetz, M.; Enke, H. (August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy & Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. ISSN 0004-6361.

[ticv8-12] Stassun, Keivan G.; et al. (2019-10-01). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. hdl:1721.1/124721. ISSN 0004-6256. S2CID 166227927.

[diaz2011-13] Díaz, C. G.; et al. (July 2011). "Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum". Astronomy & Astrophysics. 531: A143. arXiv:1012.4858. Bibcode:2011A&A...531A.143D. doi:10.1051/0004-6361/201016386. S2CID 119286673.

[Rumrill-14] Rumrill, H. B. (June 1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. 48 (283). San Francisco, California: 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681. S2CID 120743052.

[IAU-CSN-15] "IAU Catalog of Star Names". Retrieved 28 July 2016.

[WGSN-16] "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.

[TriRpt18-17] "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.

[18] Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society. 55: 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.

[baa108-19] Rogers, J. H. (1998). "Origins of the ancient constellations: II. The Mediterranean traditions". Journal of the British Astronomical Association. 108 (2): 79–89. Bibcode:1998JBAA..108...79R.

[earthsky-20] Larry Sessions. "Achernar: End of the River". EarthSky Tonight Post 06-29-2009. Retrieved 2010-02-26.

[21] (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.

[22] (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-09-03 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.

[23] "Acamar". Alcyone Bright Star Catalogue. Retrieved 2010-02-26.

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PROFILPELAJAR.COM

Theta Eridani

Nomenclature

Stellar system

Notes

References

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