Epsilon Boötis

Template:Short description Template:About-distinguish Template:Starbox begin Template:Starbox image Template:Starbox observe Template:Starbox character Template:Starbox astrometry Template:Starbox detail Template:Starbox catalog Template:Starbox reference Template:Starbox end Epsilon Boötis is a binary star system in the northern constellation of Boötes. Its name is a Bayer designation that is Latinized from ε Boötis, and abbreviated Epsilon Boo or ε Boo. The primary component has the official named Izar, pronounced Template:IPAc-en (Template:Respell).<ref name="IAU-CSN"/> 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 Template:Convert or greater is required.<ref name=monks2010/> Based on parallax measurements, it is located at a distance of Template:Convert. The system is drifting closer to the Sun with a radial velocity of −16 km/s.<ref name=Massarotti/>

NomenclatureEdit

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

It bore the traditional names Izar, Mirak and Mizar, and was named {{#invoke:Lang|lang}} Template:IPAc-en by Friedrich Georg Wilhelm von Struve.<ref>Burnham's Celestial Handbook, Vol. 1, publ. Dover Publications, Inc., 1978</ref> Izar, and Mizar are from the Template:Langx {{#invoke:Lang|lang}} and مئزر Mi'zar ('kilt like undergarment') and {{#invoke:Lang|lang}} {{#invoke:Lang|lang}} ('the loins'); {{#invoke:Lang|lang}} is Latin for 'loveliest'.<ref name=kaler/> In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name=WGSN/> 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.<ref name="IAU-CSN"/>

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}} {{#invoke:Lang|lang}}), which was translated into Latin as {{#invoke:Lang|lang}}, meaning 'belt of barker'.<ref name=Knobel1895/>

In Chinese astronomy, {{#invoke:Lang|lang}} {{#invoke:Lang|lang}} ('Celestial Lance'), refers to an asterism consisting of Epsilon Boötis, Sigma Boötis and Rho Boötis.<ref>Template:Cite book</ref> Consequently, the Chinese name for Epsilon Boötis itself is {{#invoke:Lang|lang}} {{#invoke:Lang|lang}} ('the First Star of Celestial Lance').<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

PropertiesEdit

Epsilon Boötis consists of a pair of stars with an angular separation of Template:Nowrap at a position angle of Template:Val.<ref name=Prieur2008/> The brighter component (A) has an apparent visual magnitude of 2.45,<ref name=tycho/> making it readily visible to the naked eye at night. The fainter component (B) is at magnitude 4.8,<ref name=tycho2/> which by itself would also be visible to the naked eye. Parallax measurements from the Hipparcos astrometry satellite<ref name=Perryman1997/><ref name=GSM/> put the system at a distance of about Template:Convert from the Earth.<ref name=vanLeeuwen/> 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.<ref name=kaler/>

The brighter member has a stellar classification of K0 II-III,<ref name=Luck1995/> 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. Evolutionary models suggest it is on the red giant branch, where hydrogen is being fused in a shell around a helium core.<ref name=lebre2006/> With more than four times the mass of the Sun,<ref name=Gondoin1999/> 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 Template:Val,<ref name="baines2021"/> giving it the orange hue of a K-type star.<ref name=csiro/>

The companion star has a classification of A2 V,<ref name=Cowley1969/> 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 Template:Val.<ref name=Royer2002/> It has a surface temperature of about Template:Val 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.<ref name=kaler/>

In cultureEdit

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<ref name=holm2004/> 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.<ref name=Lunan1973/> The story was even reported in Time magazine.<ref name=times1973/> 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.<ref name=AnalogSciFi/>

GalleryEdit

PositionEpsBoo.PNG

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

梗河 Gěng Hé asterism in Chinese
A photo of the star Epsilon Bootis.jpg

Epsilon Bootis (Izar) as seen in a small telescope

ReferencesEdit

Template:Reflist

External linksEdit

Template:Stars of Boötes