Beta Boötis

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Beta Boötis
Diagram showing star positions and boundaries of the Boötes constellation and its surroundings
Cercle rouge 100%.svg

A star chart showing the position of β Boötis (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Right ascension 15h 01m 56.76238s[1]
Declination +40° 23′ 26.0406″[1]
Apparent magnitude (V) 3.488[2]
Spectral type G8IIIa[3]
U−B color index +0.75[2]
B−V color index +0.94[2]
Variable type Flare star[4]
Radial velocity (Rv) –18.35[5] km/s
Proper motion (μ) RA: –40.15[1] mas/yr
Dec.: –28.86[1] mas/yr
Parallax (π) 14.48 ± 0.14[1] mas
Distance 225 ± 2 ly
(69.1 ± 0.7 pc)
Absolute magnitude (MV) –0.70[6]
Mass 3.4 ± 0.2[4] M
Radius 21.5 ± 1.0[4] R
Luminosity 170[5]–194[6] L
Surface gravity (log g) 2.40 ± 0.20[4] cgs
Temperature 4,932[5] K
Metallicity [Fe/H] –0.13[5] dex
Rotation 200 ± 10 days[4]
Rotational velocity (v sin i) 4.10 ± 1.0[4] km/s
Age 240[4]–251[6] Myr
Other designations
Nakkar, Nekkar, Merez, Meres, Merets, 42 Boötis, BD+40°2840, FK5 555, HD 133208, HIP 73555, HR 5602, SAO 45337.[3]

Beta Boötis (β Boo, β Boötis) is the Bayer designation for a star in the northern constellation of Boötes. It has an apparent visual magnitude of 3.5,[2] making it one of the brighter members of the constellation. The traditional name Nakkar or Nekkar for this star is based upon the Arabic name for the constellation.[7] This is a mis-transliteration of the Arabic بقّار baqqār "cattle driver", the Arabic letters b and n differing only in the placement of the dot.[citation needed] In the modern constellation, it marks the head of Boötis the herdsman.[7] Based upon parallax measurements, this star is approximately 225 light-years (69 parsecs) from Earth.[1] At that distance, the magnitude of the star is reduced by 0.06 from extinction caused by intervening gas and dust.[6]

Nakkar has more than three times the mass of the Sun and greater than 21 times the Sun's radius. (König et al. (2006) give it 3.4 solar masses,[4] while Tetzlaff et al. (2011) list a higher estimated mass of 5.0 ± 1.5[8] solar masses and Takeda et al. (2008) show it as 3.24[6] solar masses.) At the estimated age of 240–251 million years, it has evolved into a giant star with a stellar classification of G8 IIIa.[3] The star is radiating around 170[5]–194[6] times as much luminosity as the Sun from its outer envelope at an effective temperature of 4,932 K.[5] This heat gives it the yellow-hued glow of a G-type star. It has an estimated rotation period of about 200 days and the pole is inclined 28° ± 6° to the line of sight from the Earth.[4]

In 1993, the ROSAT satellite was used to observe an X-ray flare on Beta Boötis, which released an estimated 1.7 × 1032 erg. This was the first such observation for a low-activity star of this type. The flare may be explained by an as yet unobserved M-type dwarf companion star.[9]


  1. ^ a b c d e f van Leeuwen, F. (November 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 Fernie, J. D. (May 1983), "New UBVRI photometry for 900 supergiants", Astrophysical Journal Supplement Series 52: 7–22, Bibcode:1983ApJS...52....7F, doi:10.1086/190856 
  3. ^ a b c "bet Boo -- Flare Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-11-28 
  4. ^ a b c d e f g h i König, B. et al. (January 2006), "Spectral synthesis analysis and radial velocity study of the northern F-, G- and K-type flare stars", Monthly Notices of the Royal Astronomical Society 365 (3): 1050–1056, arXiv:astro-ph/0511232, Bibcode:2006MNRAS.365.1050K, doi:10.1111/j.1365-2966.2005.09796.x 
  5. ^ a b c d e f 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 
  6. ^ a b c d e f Takeda, Yoichi; Sato, Bun'ei; Murata, Daisuke (August 2008), "Stellar parameters and elemental abundances of late-G giants", Publications of the Astronomical Society of Japan 60 (4): 781–802, arXiv:0805.2434, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781 
  7. ^ a b Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 103, retrieved 2011-11-28 
  8. ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  9. ^ Huensch, M.; Reimers, D. (April 1995), "Detection of an X-ray flare on the low-activity G 8 III-type giant β Boo", Astronomy and Astrophysics 296: 509–513, Bibcode:1995A&A...296..509H 

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