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] |
Distance | 236 ± 8 ly (72 ± 3 pc) |
Absolute magnitude (MV) | −1.61 [8] |
Details | |
A | |
Mass | 4.6 [9] M☉ |
Radius | 37.61+1.29 −1.38 [10] R☉ |
Luminosity | 652.5±58.7 [10] L☉ |
Surface gravity (log g) | 2.24 [10] cgs |
Temperature | 4,755±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 | |
Mass | 2.27 [12] M☉ |
Radius | 2.7 [12] R☉ |
Luminosity | 44.8 [12] L☉ |
Surface gravity (log g) | 3.9 [12] cgs |
Temperature | 9,009 [12] K |
Rotational velocity (v sin i) | 123 [13] km/s |
Other designations | |
A: Izar, HD 129989, HR 5506, SAO 83500 [15] | |
B: HD 129988, HR 5505 [3] | |
Database references | |
SIMBAD | Epsilon Boo A |
Epsilon Boo B |
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 (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 : إزارʾizār and مئزر Mi'zar ('kilt like undergarment') and المراقal-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 العوّاءminṭáqa al awwa), which was translated into Latin as Cingulum Latratoris, meaning 'belt of barker'. [21]
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]
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 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]
Alpha Herculis, also designated Rasalgethi and 64 Herculis, is a multiple star system in the constellation of Hercules. Appearing as a single point of light to the naked eye, it is resolvable into a number of components through a telescope. It has a combined apparent magnitude of 3.08, although the brightest component is variable in brightness. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 360 light-years (110 parsecs) distant from the Sun. It is also close to another bright star Rasalhague in the vicinity.
Saiph, designation Kappa Orionis and 53 Orionis, is a blue supergiant star and the sixth-brightest star in the constellation of Orion. Of the four bright stars that compose Orion's main quadrangle, it is the star at the south-eastern corner. A northern-hemisphere observer facing south would see it at the lower left of Orion, and a southern-hemisphere observer facing north would see it at the upper right. Parallax measurements yield an estimated distance of 650 light-years from the Sun. It is smaller, less luminous but hotter at its surface than Rigel with an apparent visual magnitude of 2.1. The luminosity of this star changes slightly, varying by 0.04 magnitudes.
Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.58, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is half a magnitude fainter than 'β' (beta) Geminorum, Pollux.
Epsilon Sagittarii, formally named Kaus Australis, is a binary star system in the southern zodiac constellation of Sagittarius. The apparent visual magnitude of +1.85 makes it the brightest object in Sagittarius. Based upon parallax measurements, this star is around 143 light-years from the Sun.
Epsilon Pegasi, formally named Enif, is the brightest star in the northern constellation of Pegasus.
Gamma Virginis, officially named Porrima, is a binary star system in the constellation of Virgo. It consists of two almost identical main sequence stars at a distance of about 38 light-years.
Lambda Sagittarii, formally named Kaus Borealis, is a star in the southern constellation of Sagittarius. The star marks the top of the Archer's bow.
Theta Eridani, Latinized from θ Eridani, is a binary system in the constellation of Eridanus with a combined apparent magnitude of 2.88. Its two components are designated θ1 Eridani, formally named Acamar, and θ2 Eridani. The system's distance from the Sun based on parallax measurements is approximately 165 light-years.
Beta Aquarii is a single yellow supergiant star in the constellation of Aquarius. It has the official name Sadalsuud and the Bayer designation β Aquarii, abbreviated Beta Aqr or β Aqr. Based upon parallax measurements obtained during the Hipparcos mission, this component is located at a distance of approximately 540 light years (165 parsecs) from the Sun. It is drifting further away with a radial velocity of 6.5 km/s. The star serves as an IAU radial velocity standard.
Epsilon Aquarii, Latinized from ε Aquarii, is a binary star in the equatorial zodiac constellation of Aquarius, located near the western constellation border with Capricornus. It has the proper name Albali, now formally recognized by the IAU. It is visible to the naked eye with an apparent visual magnitude of 3.77, and has an absolute magnitude of −0.46. Based upon parallax measurements taken by the Gaia spacecraft, it is located at a distance of approximately 244 light-years (75 pc) from Earth. The star is drifting closer with a radial velocity of −20 km/s.
Alpha Crateris, officially named Alkes, is a star in the constellation of Crater. It is a cool giant star about 43.2 parsecs (141 ly) away.
Epsilon Cancri is a white-hued binary star system in the zodiac constellation of Cancer. It is the brightest member of the Beehive Cluster with an apparent visual magnitude of +6.29, which is near the lower limit of visibility with the naked eye. The annual parallax shift of 5.4 mas as seen from Earth yields a distance estimate of approximately 606 light-years from the Sun.
Iota Andromedae is a single star in the northern constellation of Andromeda. It has the Flamsteed designation 17 Andromedae, while Iota Andromedae is the Bayer designation as Latinized from ι Andromedae. This object is visible to the naked eye at night as a faint, blue-white hued star with an apparent visual magnitude of +4.29. Based upon parallax measurements, it is located approximately 500 light years distant from the Sun.
Gamma Boötis, Latinised from γ Boötis, is a binary star system in the northern constellation of Boötes the herdsman, forming the left shoulder of this asterism. The primary component has the proper name Seginus, the traditional name of the Gamma Bootis system. It has a white hue and is visible to the naked eye with a typical apparent visual magnitude of +3.03. Based on parallax measurements obtained during the Hipparcos mission, it is located at a distance of approximately 85 light-years from the Sun, but is drifting closer with a radial velocity of −32 km/s.
Eta Boötis is a binary star in the constellation of Boötes. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 37 light-years distant from the Sun. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It forms a double star with the star BD+19 2726.
Mu Boötis, Latinized from μ Boötis, consists of a pair of double stars in the northern constellation of Boötes, 120 light-years from the Sun.
38 Boötis is a single star in the northern constellation of Boötes, located approximately 157 light years from the Sun. It has the traditional name Merga and the Bayer designation h Boötis; 38 Boötis is the star's Flamsteed designation. This object is visible to the naked eye as a dim, yellow-white hued star with an apparent visual magnitude of 5.76. It is moving closer to the Earth with a heliocentric radial velocity of −4.5 km/s.
Omicron2 Canis Majoris is a star in the constellation Canis Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It has an apparent visual magnitude of 3.043, making it one of the brighter members of the constellation. Based upon a distance modulus of 10.2, it is about 3,600 light-years from Earth.
Epsilon Delphini, officially named Aldulfin, is a solitary, blue-white hued star in the northern constellation of Delphinus. It is visible to the naked eye with an apparent visual magnitude of 4.03. Based upon an annual parallax shift of 9.87 mas as seen from the Earth, the system is located about 330 light-years from the Sun. At Epsilon Delphini's distance, the visual magnitude is diminished by an extinction factor of 0.11 due to interstellar dust. The star is moving closer to the Sun with a radial velocity of −19 km/s.
Theta Ceti, Latinized from θ Ceti, is a solitary, orange-hued star in the equatorial constellation of Cetus. It is visible to the naked eye with an apparent visual magnitude of 3.60. Based upon an annual parallax shift of 20m04 mas as seen from Earth, it is located about 113 light-years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.28 due to interstellar dust.