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Epsilon Boötis

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This article is about Izar. Not to be confused with Mizar.

Epsilon Boötis (ε Boötis, abbreviated Epsilon Boo, ε Boo), officially named Izar (/ˈaɪzɑːr/ EYE-zar),[16] is a binary star in the northern constellation of Boötes. The star system can be viewed with the unaided eye at night, but resolving the pair with a small telescope is challenging; an aperture of 76 mm (3.0 in) or greater is required.[17]

ε Boötis
Location of ε Boötis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Right ascension 14h 44m 59.22s[1]
Declination +27° 04′ 27.2″[1]
Apparent magnitude (V) 2.37[2]/5.12[3]
Characteristics
Spectral type K0 II-III[4] + A2 V[5]
U−B color index +0.73[2]
B−V color index +0.97[2]
Astrometry
Radial velocity (Rv)−16.31[6] km/s
Proper motion (μ) RA: −50.95[1] mas/yr
Dec.: +21.07[1] mas/yr
Parallax (π)13.8267 ± 0.4896 mas[7]
Distance236 ± 8 ly
(72 ± 3 pc)
Absolute magnitude (MV)−1.61[8]
Details
A
Mass4.6[9] M☉
Radius37.61+1.29
−1.38[10] R☉
Luminosity652.5±58.7[10] L☉
Surface gravity (log g)2.24[10] cgs
Temperature4,755±46[10] K
Metallicity–0.13[6]
Metallicity [Fe/H]–0.20[11] dex
Rotational velocity (v sin i)10.9[6] km/s
B
Mass2.27[12] M☉
Radius2.7[12] R☉
Luminosity44.8[12] L☉
Surface gravity (log g)3.9[12] cgs
Temperature9,009[12] K
Rotational velocity (v sin i)123[13] km/s
Other designations
Izar, Pulcherrima, Mirac, Mirak, Mirach, ε Boo, 36 Boo, BD+27°2417, HIP 72105[14]
A: Izar, HD 129989, HR 5506, SAO 83500[15]
B: HD 129988, HR 5505[3]
Database references
SIMBADEpsilon Boo A
Epsilon Boo B

Nomenclature

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Illustration of the two components of Epsilon Boötis (north is up)

ε Boötis (Latinised to Epsilon Boötis) is the star's Bayer designation.

It bore the traditional names Izar, Mirak and Mizar, and was named Pulcherrima /pəlˈkɛrɪmə/ by Friedrich Georg Wilhelm von Struve.[18] Izar, and Mizar are from the Arabic: إزار ʾizār and مئزر Mi'zar ('kilt like undergarment') and المراق al-maraqq' ('the loins'); Pulcherrima is Latin for 'loveliest'.[19] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[20] to catalogue and standardize proper names for stars. The WGSN approved the name Izar for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[16]

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Mintek al Aoua (منطقة العوّاء minṭáqa al awwa), which was translated into Latin as Cingulum Latratoris, meaning 'belt of barker'.[21]

 
梗河 Gěng Hé asterism in Chinese

In Chinese astronomy, 梗河 Gěng Hé ('Celestial Lance'), refers to an asterism consisting of Epsilon Boötis, Sigma Boötis and Rho Boötis.[22] Consequently, the Chinese name for Epsilon Boötis itself is 梗河一 Gěng Hé yī ('the First Star of Celestial Lance').[23]

Properties

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Epsilon Bootis (Izar) as seen in a small telescope

Epsilon Boötis consists of a pair of stars with an angular separation of 2.852 ± 0.014 arcseconds at a position angle of 342.°9 ± 0.°3.[24] The brighter component (A) has an apparent visual magnitude of 2.37,[2] making it readily visible to the naked eye at night. The fainter component (B) is at magnitude 5.12,[3] which by itself would also be visible to the naked eye. Parallax measurements from the Hipparcos astrometry satellite[25][26] put the system at a distance of about 203 light-years (62 parsecs) from the Earth.[1] This means the pair has a projected separation of 185 Astronomical Units, and they orbit each other with a period of at least 1,000 years.[19]

The brighter member has a stellar classification of K0 II-III,[4] which means it is a fairly late-stage star well into its stellar evolution, having already exhausted its supply of hydrogen fuel at the core. With more than four times the mass of the Sun,[9] it has expanded to about 38 times the Sun's radius and is emitting 650 times the luminosity of the Sun. This energy is being radiated from its outer envelope at an effective temperature of 4,755 K,[10] giving it the orange hue of a K-type star.[27]

The companion star has a classification of A2 V,[5] so it is a main sequence star that is generating energy through the thermonuclear fusion of hydrogen at its core. This star is rotating rapidly, with a projected rotational velocity of 123 km/s.[13] It has a surface temperature of about 9,000 K and a radius nearly three times the Sun, leading to a bolometric luminosity 45 times that of the Sun.

By the time the smaller main sequence star reaches the current point of the primary in its evolution, the larger star will have lost much of its mass in a planetary nebula and will have evolved into a white dwarf. The pair will have essentially changed roles: the brighter star becoming the dim dwarf, while the lesser companion will shine as a giant star.[19]

In culture

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In 1973, the Scottish astronomer and science fiction writer Duncan Lunan claimed to have managed to interpret a message caught in the 1920s by two Norwegian physicists[28] that, according to his theory, came from a 13,000 year old satellite polar orbiting the Earth known as the Black Knight and sent there by the inhabitants of a planet orbiting Epsilon Boötis.[29] The story was even reported in Time magazine.[30] Lunan later withdrew his Epsilon Boötis theory, presenting proofs against it and clarifying why he was brought to formulate it in the first place, but later revoked his withdrawal.[31]

References

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  1. ^ a b c d e van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. ^ a b c d Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99–110. Bibcode:1966CoLPL...4...99J.
  3. ^ a b c "HR 5506 -- Star in double system". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-01-09.
  4. ^ a b Luck, R. Earle; Wepfer, Gordon G. (November 1995). "Chemical Abundances for F and G Luminosity Class II Stars". The Astronomical Journal. 110: 2425. Bibcode:1995AJ....110.2425L. doi:10.1086/117702.
  5. ^ a b Cowley, A.; et al. (April 1969). "A study of the bright A stars. I. A catalogue of spectral classifications". The Astronomical Journal. 74: 375–406. Bibcode:1969AJ.....74..375C. doi:10.1086/110819.
  6. ^ a b c Massarotti, Alessandro; et al. (January 2008). "Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity". The Astronomical Journal. 135 (1): 209–231. Bibcode:2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209. S2CID 121883397.
  7. ^ 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.
  8. ^ Anderson, E.; Francis, Ch. (25 May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  9. ^ a b Gondoin, P. (December 1999). "Evolution of X-ray activity and rotation on G-K giants". Astronomy and Astrophysics. 352: 217–227. Bibcode:1999A&A...352..217G.
  10. ^ a b c d e Baines, Ellyn K.; Thomas Armstrong, J.; Clark, James H.; Gorney, Jim; Hutter, Donald J.; Jorgensen, Anders M.; Kyte, Casey; Mozurkewich, David; Nisley, Ishara; Sanborn, Jason; Schmitt, Henrique R. (November 2021). "Angular Diameters and Fundamental Parameters of Forty-four Stars from the Navy Precision Optical Interferometer". The Astronomical Journal. 162 (5): 198. arXiv:2211.09030. Bibcode:2021AJ....162..198B. doi:10.3847/1538-3881/ac2431. ISSN 0004-6256. S2CID 238998021.
  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. (2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy and Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. S2CID 131780028.
  12. ^ a b c d e Stassun K.G.; et al. (October 2019). "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. S2CID 166227927.
  13. ^ a b Royer, F.; et al. (October 2002). "Rotational velocities of A-type stars. II. Measurement of v sin i in the northern hemisphere". Astronomy and Astrophysics. 393 (3): 897–911. arXiv:astro-ph/0205255. Bibcode:2002A&A...393..897R. doi:10.1051/0004-6361:20020943. S2CID 14070763.
  14. ^ "CCDM J14449+2704AB". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-01-09.
  15. ^ "HR 5505 -- Star in double system". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-01-09.
  16. ^ a b "IAU Catalog of Star Names" (TXT). Archived from the original on 2016-08-12. Retrieved 28 July 2016.
  17. ^ Monks, Neale (September 2010). Go-To Telescopes Under Suburban Skies. Patrick Moore's Practical Astronomy Series. Springer. p. 110. ISBN 978-1-4419-6850-0.
  18. ^ Burnham's Celestial Handbook, Vol. 1, publ. Dover Publications, Inc., 1978
  19. ^ a b c Kaler, James B. "Izar". Stars. University of Illinois. Archived from the original on 2012-06-03. Retrieved 2012-01-09.
  20. ^ "IAU working group on star names (WGSN)". Retrieved 22 May 2016.
  21. ^ 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 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
  22. ^ 陳久金 (2005). 中國星座神話 (in Chinese). 台灣書房出版有限公司. ISBN 978-986-7332-25-7.
  23. ^ "研究資源 – 亮星中英對照表". 香港太空館 [Hong Kong Space Museum] (in Chinese). Archived from the original on 2011-01-29. Retrieved 2010-11-23.
  24. ^ Prieur, J.-L.; et al. (22 May 2008). "Speckle observations with PISCO in Merate – V. Astrometric measurements of visual binaries in 2006". Monthly Notices of the Royal Astronomical Society. 387 (2): 772–782. Bibcode:2008MNRAS.387..772P. doi:10.1111/j.1365-2966.2008.13265.x.
  25. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; et al. (July 1997). "The Hipparcos Catalogue". Astronomy and Astrophysics. 323: L49 – L52. Bibcode:1997A&A...323L..49P.
  26. ^ Perryman, Michael (2010). The Making of History's Greatest Star Map. Astronomers' Universe. Heidelberg: Springer-Verlag. Bibcode:2010mhgs.book.....P. doi:10.1007/978-3-642-11602-5. ISBN 978-3-642-11601-8.
  27. ^ "The Colour of Stars". Australia Telescope, Outreach and Education. Commonwealth Scientific and Industrial Research Organisation. 21 December 2004. Archived from the original on 2012-03-18. Retrieved 2012-01-16.
  28. ^ Holm, Sverre (16 March 2004). "The Five Most Likely Explanations for Long Delayed Echoes". Archived from the original on 2009-11-13. Retrieved 2009-09-01.
  29. ^ Lunan, Duncan (April 1973). "Spaceprobe from Epsilon Boötes". Spaceflight. 15 (4). London, England: British Interplanetary Society.
  30. ^ "Message from a Star". Time. 9 April 1973. Archived from the original on 2010-04-29. Retrieved 2009-08-27.
  31. ^ Lunan, Duncan (March 1998). "Epsilon Boötis Revisited". Analog Science Fiction and Fact. Vol. 118, no. 3. Archived from the original on 2020-10-05.
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