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]
Database references

Beta Boötis (β Boötis, abbreviated Beta Boo, β Boo), also named Nekkar,[7] is 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. In the modern constellation, it marks the head of Boötis the herdsman.[8] Based upon parallax measurements, this star is approximately 225 light-years (69 parsecs) from the Sun.[1] At that distance, the magnitude of the star is reduced by 0.06 from extinction caused by intervening gas and dust.[6]


β Boötis (Latinised to Beta Boötis) is the star's Bayer designation.

It bore the traditional name Nekkar or Nakkar derived from the Arabic name for the constellation: Al Baḳḳār 'the Herdsman'.[8] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[9] to catalogue and standardize proper names for stars. The WGSN approved the name Nekkar for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.[7]


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[10] 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.[11]


  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:0708.1752Freely accessible. 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/0511232Freely accessible, 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:0805.2434Freely accessible, Bibcode:2008PASJ...60..781T, doi:10.1093/pasj/60.4.781 
  7. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  8. ^ a b Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 103, retrieved 2011-11-28 
  9. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016. 
  10. ^ 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:1007.4883Freely accessible, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x 
  11. ^ 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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