Epsilon Boötis is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

system in the northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Boötes Boötes ( ) is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from , which comes from 'herder, herdsman' or 'plowman' (literally, 'o ...

. Its name is a

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

that is Latinized from ε Boötis, and abbreviated Epsilon Boo or ε Boo. The primary component has the official named Izar, pronounced (). The star system can be viewed with the unaided eye at night, but resolving the pair with a small telescope is challenging; an

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

of or greater is required. Based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements, it is located at a distance of . The system is drifting closer to the Sun with a

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of −16 km/s.

Nomenclature

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

. It bore the traditional names ''Izar'', ''Mirak'' and ''Mizar'', and was named by

Friedrich Georg Wilhelm von Struve Friedrich Georg Wilhelm von Struve (, trans. ''Vasily Yakovlevich Struve''; 15 April 1793 – ) was a Baltic German astronomer and geodesist. He is best known for studying double stars and initiating a triangulation survey later named Struve ...

. ''Izar'', and ''Mizar'' are from the and مئزر ''Mi'zar'' ('kilt like undergarment') and ('the loins'); is

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for 'loveliest'. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(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. In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', this star was designated ( ), which was translated into

as , meaning 'belt of barker'. In

Chinese astronomy Astronomy in China has a long history stretching from the Shang dynasty, being refined over a period of more than 3,000 years. The Ancient China, ancient Chinese people have identified stars from 1300 BCE, as Chinese star names later categori ...

, (' Celestial Lance'), refers to an asterism consisting of Epsilon Boötis, Sigma Boötis and Rho Boötis. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Epsilon Boötis itself is ('the First Star of Celestial Lance').

Properties

Epsilon Boötis consists of a pair of stars with an

angular separation Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...

of at a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...

of . The brighter component (A) has an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 2.45, making it readily visible to the naked eye at night. The fainter component (B) is at magnitude 4.8, which by itself would also be visible to the naked eye.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements from the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

astrometry satellite put the system at a distance of about from the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. This means the pair has a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outs ...

of 185

Astronomical Unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s, and they orbit each other with a period of at least 1,000 years. The brighter member has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of K0 II-III, which means it is a fairly late-stage star well into its

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...

, having already exhausted its supply of

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

fuel at the core. Evolutionary models suggest it is on the

red giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass st ...

, where hydrogen is being fused in a shell around a helium core. With more than four times the

mass of the Sun The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...

, it has expanded to about 38 times the

Sun's radius Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: 1\,R_ = 6.957\ti ...

and is emitting 650 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

. This energy is being radiated from its outer envelope at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of , giving it the orange hue of a

K-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

. The companion star has a classification of A2 V, so it is a

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

star that is generating energy through the

thermonuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nuclei, nuclei/neutron by-products. The difference in mass between the reactants and products is manifested as either the release or absorption of ener ...

of hydrogen at its core. This star is rotating rapidly, with a projected rotational velocity of . It has a surface temperature of about and a radius nearly three times the Sun, leading to a

bolometric luminosity Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electromagnetic energy emitted per ...

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 A planetary nebula is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets. The ...

and will have evolved into a

white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...

. The pair will have essentially changed roles: the brighter star becoming the dim dwarf, while the lesser companion will shine as a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

In culture

In 1973, the

Scottish Scottish usually refers to something of, from, or related to Scotland, including: *Scottish Gaelic, a Celtic Goidelic language of the Indo-European language family native to Scotland *Scottish English *Scottish national identity, the Scottish ide ...

astronomer and science fiction writer

Duncan Lunan Duncan Alasdair Lunan, born October 1945, is a Scottish author with emphasis on astronomy, spaceflight and science fiction, undertaking a wide range of writing and speaking on those and other topics as a researcher, tutor, critic, editor, lecture ...

claimed to have managed to interpret a message caught in the 1920s by two Norwegian physicists that, according to his theory, came from a 13,000 year old satellite polar orbiting the Earth known as the

Black Knight The black knight is a literary stock character who masks his identity and that of his liege by not displaying heraldry. Black knights are usually portrayed as villainous figures who use this anonymity for misdeeds. They are often contrasted with ...

and sent there by the inhabitants of a planet orbiting Epsilon Boötis. The story was even reported in ''

Time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...

'' magazine. 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.

Gallery

PositionEpsBoo.PNG, Illustration of the two components of Epsilon Boötis (north is up) Genghe.png, alt=Epsilon Boötis (ε Boötis) là 梗河一, 梗河 ''Gěng Hé asterism in Chinese'' A photo of the star Epsilon Bootis.jpg, Epsilon Bootis (Izar) as seen in a small telescope

References

External links

Information page for HR 5506 (Izar) on VizieR

Information page for HR 5505 (ε Boötes B) on VizieR

Information page for CCDM J14449+2704 (all component stars) on VizieR

Image of Epsilon Boötis

Izar star chart with viewing information on in-the-sky.org

ε Boötes B star chart with viewing information on in-the-sky.org
{{DEFAULTSORT:Epsilon Bootis K-type bright giants K-type giants A-type main-sequence stars Binary stars Boötes Bootis, Epsilon 5505 6 BD+27 2417 Bootis, 36 129988 9 072105 Izar