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Theta Eridani

March 11, 2023

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.

Theta Eridani
Location of θ Eridani (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Eridanus
θ1 Eri
Right ascension 02h 58m 15.6764s[1]
Declination −40° 18′ 16.839″[1]
Apparent magnitude (V) 3.18[2]
θ2 Eri
Right ascension 02h 58m 16.4037s[3]
Declination −40° 18′ 16.906″[3]
Apparent magnitude (V) 4.11[2]
Characteristics
θ1 Eri
Spectral type A3IV-V[4]
U−B color index +0.14[5]
B−V color index +0.128±0.012[6]
θ2 Eri
Spectral type A1V[4]
B−V color index +0.08[5]
Variable type suspected[7]
Astrometry
θ1 Eri
Radial velocity (Rv)+11.9±2.6[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]
Distance164 ± 2 ly
(50.2 ± 0.5 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]
Distance167 ± 1 ly
(51.2 ± 0.4 pc)
Absolute magnitude (MV)−0.59 (combined)[6]
Details
θ1 Eri
Mass2.6[8] M☉
Luminosity145[6] L☉
Temperature8,200[8] K
Rotational velocity (v sin i)65.1[9] km/s
θ2 Eri
Mass1.95[10] M☉
Radius2.7[11] R☉
Luminosity37[11] L☉
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
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
SIMBADθ1 Eri
θ2 Eri

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]

Ptolemy described Theta Eridani as a first-magnitude star, which some have taken to be, in fact, Achernar, which today appears just above the horizon in Alexandria where Ptolemy lived. Achernar, however, was not visible to Ptolemy (it is from Alexandria today due to precession); its declination in 100 CE was −67, making it invisible even at Aswan. Ptolemy's Eridanus, thus, without doubt, ended at Theta Eridani, which rose about 10 degrees above the horizon from Alexandria. This fact besides positively identifying Theta Eridani as the original "end of the river", also strengthens the case for it having been first magnitude in ancient times.[citation needed]

References

  1. ^ 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.
  2. ^ 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ a b Hoffleit; et al. (1991). "Bright Star Catalogue". VizieR (5th Revised ed.). Centre de Données astronomiques de Strasbourg. Retrieved 2010-02-24.
  6. ^ a b c d e 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.
  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 Kaler, James B. "ACAMAR (Theta Eridani)". Stars. University of Illinois. Retrieved 2010-02-24.
  9. ^ 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.
  10. ^ 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.
  11. ^ 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.
  12. ^ 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.
  13. ^ Rumrill, H. B. (June 1936). "Star Name Pronunciation". Publications of the Astronomical Society of the Pacific. San Francisco, California. 48 (283): 139. Bibcode:1936PASP...48..139R. doi:10.1086/124681. S2CID 120743052.
  14. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016.
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  17. ^ 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.
  18. ^ 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.
  19. ^ Larry Sessions. "Achernar: End of the River". EarthSky Tonight Post 06-29-2009. Retrieved 2010-02-26.
  20. ^ (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.
  21. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 2010-09-03 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  22. ^ "Acamar". Alcyone Bright Star Catalogue. Retrieved 2010-02-26.

March 11, 2023
theta, eridani, latinized, from, eridani, binary, system, constellation, eridanus, with, combined, apparent, magnitude, components, designated, eridani, formally, named, acamar, ɑːr, traditional, name, system, eridani, system, distance, from, based, parallax, . Theta Eridani Latinized from 8 Eridani is a binary system in the constellation of Eridanus with a combined apparent magnitude of 2 88 6 Its two components are designated 81 Eridani formally named Acamar ˈ ae k e m ɑːr the traditional name of the system 13 14 and 82 Eridani The system s distance from the Sun based on parallax measurements is approximately 165 light years Theta EridaniLocation of 8 Eridani circled Observation dataEpoch J2000 Equinox J2000Constellation Eridanus81 EriRight ascension 02h 58m 15 6764s 1 Declination 40 18 16 839 1 Apparent magnitude V 3 18 2 82 EriRight ascension 02h 58m 16 4037s 3 Declination 40 18 16 906 3 Apparent magnitude V 4 11 2 Characteristics81 EriSpectral type A3IV V 4 U B color index 0 14 5 B V color index 0 128 0 012 6 82 EriSpectral type A1V 4 B V color index 0 08 5 Variable type suspected 7 Astrometry81 EriRadial velocity Rv 11 9 2 6 6 km sProper motion m RA 57 132 1 mas yr Dec 23 058 1 mas yrParallax p 19 9047 0 2062 mas 1 Distance164 2 ly 50 2 0 5 pc 82 EriProper motion m RA 50 502 3 mas yr Dec 16 613 3 mas yrParallax p 19 5270 0 1372 mas 3 Distance167 1 ly 51 2 0 4 pc Absolute magnitude MV 0 59 combined 6 Details81 EriMass2 6 8 M Luminosity145 6 L Temperature8 200 8 KRotational velocity v sin i 65 1 9 km s82 EriMass1 95 10 M Radius2 7 11 R Luminosity37 11 L Surface gravity log g 3 83 10 cgsTemperature8 293 10 KMetallicity Fe H 0 197 10 dexRotational velocity v sin i 102 5 12 km sOther designationsTheta Eri 8 Eri CD 40 771 HIP 13847 SAO 216113 CCDM J02583 4018 WDS 02583 401881 Eri Acamar HD 18622 HR 89782 Eri HD 18623 HR 898Database referencesSIMBAD81 Eri82 EriNomenclature EditTheta Eridani is the system s Bayer designation 81 and 82 Eridani those of its two components The system bore the traditional name Acamar derived from the Arabic آخ ر الن ه ر citation needed Akhir 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 81 Eridani on 20 July 2016 and it is now so entered in the IAU Catalog of Star Names 14 The term Akhir 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 gt 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 Tian Yuan 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 Tian Yuan liu English the Sixth Star of Celestial Orchard 21 Stellar system EditTheta Eridani is a binary system with some evidence suggesting it is part of a multiple star system 7 22 The main star 81 Eridani is of spectral class A4 with a 3 2 apparent magnitude Its companion star 82 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 Ptolemy described Theta Eridani as a first magnitude star which some have taken to be in fact Achernar which today appears just above the horizon in Alexandria where Ptolemy lived Achernar however was not visible to Ptolemy it is from Alexandria today due to precession its declination in 100 CE was 67 making it invisible even at Aswan Ptolemy s Eridanus thus without doubt ended at Theta Eridani which rose about 10 degrees above the horizon from Alexandria This fact besides positively identifying Theta Eridani as the original end of the river also strengthens the case for it having been first magnitude in ancient times citation needed References Edit 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 amp Astrophysics 649 A1 arXiv 2012 01533 Bibcode 2021A amp 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 Hog 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 amp 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 amp Astrophysics 649 A1 arXiv 2012 01533 Bibcode 2021A amp 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 Donnees astronomiques de Strasbourg Retrieved 2010 02 24 a b c d e 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 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 amp Astrophysics 542 A116 arXiv 1204 2459 Bibcode 2012A amp 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 Matijevic G Monari G Cantat Gaudin T Weiler M Khan S Miglio A Carrillo I Romero Gomez 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 amp Astrophysics 628 A94 arXiv 1904 11302 Bibcode 2019A amp 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 Diaz C G et al July 2011 Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum Astronomy amp Astrophysics 531 A143 arXiv 1012 4858 Bibcode 2011A amp 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 San Francisco California 48 283 139 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 Retrieved from https en wikipedia org w index php title Theta Eridani amp oldid 1141729413, wikipedia, wiki, book, books, library,

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