| absmag_v = −1.61[13]
}}{{Starbox detail
| component1 = A
| mass = 4.6[14]
| radius = 33[9]
| luminosity = 501[9]
| temperature = 4,550[9]
| gravity = 2.2[9]
| metal = –0.13[9]
| rotational_velocity = 10.9[9]
| age_myr = {{nowrap|37.4 ± 4.2}}[21]
| component2 = B
| rotational_velocity2 = 123[22]
}}{{Starbox catalog
| names = ε Boo, Izar, Pulcherrima, Mirac, Mirak, Mirach, 36 Boo, BD+27° 2417, HIP 72105[23]
A: HD 129989, HR 5506, SAO 83500.[24]
B: HD 129988, HR 5505.[4]
}}{{Starbox reference
|Simbad=eps+Boo
}}{{Starbox end}}Epsilon Boötis (ε Boötis, abbreviated Epsilon Boo, ε Boo), also named Izar,[1] 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 {{Convert|76|mm|in|abbr=on}} or greater is required.[27]Nomenclature
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 by Otto Struve.[2] Izar, Mirak and Mizar are from the Arabic إزار ’izār 'veil' and المراق al-maraqq 'the loins'; 'Pulcherrima' is Latin for 'loveliest'.[29] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[3] 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.[1]
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.[32]
In Chinese, {{lang|zh|梗河}} ({{lang|zh-Latn|Gěng Hé}}), meaning Celestial Lance, refers to an asterism consisting of Epsilon Boötis, Sigma Boötis and Rho Boötis.[4] Consequently, Epsilon Boötis itself is known as {{lang|zh|梗河一}} ({{lang|zh-Latn|Gěng Hé yī}}, {{lang-en|the First Star of Celestial Lance}}.)[5]
Properties
Epsilon Boötis consists of a pair of stars with an angular separation of {{nowrap|2.852 ± 0.014 arcseconds}} at a position angle of {{nowrap|342.°9 ± 0.°3}}.[35] The brighter component (A) has an apparent visual magnitude of 2.37,[3] making it readily visible to the naked eye at night. The fainter component (B) is at magnitude 5.12,[4] which by itself would also be visible to the naked eye. Parallax measurements from the Hipparcos astrometry satellite[38][39] put the system at a distance of about {{Convert|203|ly|pc|abbr=off|lk=on}} from the Earth.[ 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.[29]]
The brighter member has a stellar classification of K0 II-III,[5] 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,[14] it has expanded to about 33 times the Sun's radius and is emitting 501 times the luminosity of the Sun.[9] This energy is being radiated from its outer envelope at an effective temperature of 4,550 K,[9] giving it the orange hue of a K-type star.[46]
The companion star has a classification of A2 V,[6] 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 {{nowrap|123 km s−1}}[22] 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.[29]
In culture
{{see also|Epsilon Boötis in fiction}}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[50] that, according to his theory, came from a 10,000 year old satellite polar orbiting the Earth known as the Black Knight and sent there by the inhabitants of a planet orbiting Epsilon Boötis.[6] The story was even reported in Time magazine.[52] 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 would later go on to suspiciously revoke his withdrawal.[53]
References
1. ^1 {{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |accessdate=28 July 2016}}
2. ^Norton's Star Atlas, publ. Gall & Inglis, Edinburgh, 2nd Ed., 1959
3. ^{{cite web|url=https://www.iau.org/science/scientific_bodies/working_groups/280/|title=IAU working group on star names (WGSN)|accessdate=22 May 2016}}
4. ^{{zh icon}} 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}}.
5. ^{{zh icon}} 香港太空館 - 研究資源 - 亮星中英對照表 {{webarchive |url=https://web.archive.org/web/20110129031951/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_h_l.htm |date=January 29, 2011 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.
6. ^{{cite journal|first=Duncan|last=Lunan|title=Spaceprobe from Epsilon Bootes|journal=Spaceflight|publisher=British Interplanetary Society|date=April 1973|volume=15|number=4|location=London, England}}
7. ^1 {{citation | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | postscript=. }}
8. ^1 2 3 4 5 6 7 8 9 {{citation | display-authors=1 | last1=Massarotti | first1=Alessandro | last2=Latham | first2=David W. | last3=Stefanik | first3=Robert P. | last4=Fogel | first4=Jeffrey | title=Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity | journal=The Astronomical Journal | volume=135 | issue=1 | pages=209–231 |date=January 2008 | doi=10.1088/0004-6256/135/1/209 | bibcode=2008AJ....135..209M }}
9. ^1 2 3 4 {{cite journal | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | year=1966 | bibcode=1966CoLPL...4...99J }}
10. ^1 {{citation | last1=Perryman | first1=M. A. C. | last2=Lindegren | first2=L. | last3=Kovalevsky | first3=J. | title=The Hipparcos Catalogue | journal=Astronomy and Astrophysics | volume=323 |date=July 1997 | pages=L49–L52 | bibcode=1997A&A...323L..49P|display-authors=etal}}
11. ^1 2 {{citation | display-authors=1 | last1=Cowley | first1=A. | last2=Cowley | first2=C. | last3=Jaschek | first3=M. | last4=Jaschek | first4=C. | title=A study of the bright A stars. I. A catalogue of spectral classifications | journal=Astronomical Journal | volume=74 | pages=375–406 |date=April 1969 | doi=10.1086/110819 | bibcode=1969AJ.....74..375C }}
12. ^1 {{citation | last=Perryman | first=Michael | title=The Making of History's Greatest Star Map | location=Heidelberg | publisher=Springer-Verlag | year=2010 | doi=10.1007/978-3-642-11602-5}}
13. ^1 2 {{citation | display-authors=1 | last1=Royer | first1=F. | last2=Grenier | first2=S. | last3=Baylac | first3=M.-O. | last4=Gómez | first4=A. E. | last5=Zorec | first5=J. | title=Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i | journal=Astronomy and Astrophysics | volume=393 | pages=897–911 |date=October 2002 | doi=10.1051/0004-6361:20020943 | bibcode=2002A&A...393..897R |arxiv = astro-ph/0205255 }}
14. ^1 2 {{citation | last1=Luck | first1=R. Earle | last2=Wepfer | first2=Gordon G. | title=Chemical Abundances for F and G Luminosity Class II Stars | journal=Astronomical Journal | volume=110 | page=2425 |date=November 1995 | doi=10.1086/117702 | bibcode=1995AJ....110.2425L }}
15. ^1 {{citation | display-authors=1 | last1=Prieur | first1=J.-L. | last2=Scardia | first2=M. | last3=Pansecchi | first3=L. | last4=Argyle | first4=R. W. | last5=Sala | first5=M. | last6=Ghigo | first6=M. | last7=Koechlin | first7=L. | last8=Aristidi | first8=E. | title=Speckle observations with PISCO in Merate - V. Astrometric measurements of visual binaries in 2006 | journal=Monthly Notices of the Royal Astronomical Society | volume=387 | issue=2 | pages=772–782 |date=June 2008 | doi=10.1111/j.1365-2966.2008.13265.x | bibcode=2008MNRAS.387..772P }}
16. ^1 {{citation | title=CCDM J14449+2704AB | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=CCDM+J14449 | accessdate=2012-01-09 }}
17. ^1 {{citation | title=HR 5505 -- Star in double system | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HR+5505 | accessdate=2012-01-09 }}
18. ^1 2 3 {{citation | title=HR 5506 -- Star in double system | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HR+5505 | accessdate=2012-01-09 }}
19. ^1 2 3 {{citation | first1=James B. | last1=Kaler | title=Izar | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/izar.html | accessdate=2012-01-09 }}
20. ^1 {{citation | last1=Tetzlaff | first1=N. | last2=Neuhäuser | first2=R. | last3=Hohle | first3=M. M. | title=A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun | journal=Monthly Notices of the Royal Astronomical Society | volume=410 | issue=1 | pages=190–200 |date=January 2011 | doi=10.1111/j.1365-2966.2010.17434.x | bibcode=2011MNRAS.410..190T |arxiv = 1007.4883 }}
21. ^1 {{citation | last=Knobel | first=E. B. | title=Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket | journal=Monthly Notices of the Royal Astronomical Society | volume=55 | page=429 |date=June 1895 | bibcode=1895MNRAS..55..429K | doi=10.1093/mnras/55.8.429}}
22. ^1 {{citation | url=http://heim.ifi.uio.no/~sverre/LDE/ | title=The Five Most Likely Explanations for Long Delayed Echoes | first1=Sverre | last1=Holm |date=March 16, 2004 | accessdate=2009-09-01 }}
23. ^1 {{citation | url=http://www.time.com/time/magazine/article/0,9171,903951-1,00.html | title=Message from a Star |date=April 9, 1973 | accessdate=2009-08-27 | work=Time }}
24. ^1 {{citation | journal=Analog Science Fiction and Fact | volume=118 | issue=3 |date=March 1998 | title=Epsilon Boötis Revisited | first1=Duncan | last1=Lunan }}
25. ^1 {{citation | first1=Neale | last1=Monks | title=Go-To Telescopes Under Suburban Skies | series=Patrick Moore's Practical Astronomy Series | publisher=Springer | year=2010 | isbn=1-4419-6850-4 | url=https://books.google.com/books?id=waO6tUtfblsC&pg=PA110 |page=110}}
26. ^1 {{citation |title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |accessdate=2012-01-16 |deadurl=yes |archiveurl=https://www.webcitation.org/6630AbtJZ?url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archivedate=2012-03-10 |df= }}
27. ^1 2 {{citation | last1=Gondoin | first1=P. | title=Evolution of X-ray activity and rotation on G-K giants | journal=Astronomy and Astrophysics | volume=352 | pages=217–227 |date=December 1999 | bibcode=1999A&A...352..217G }}