Beta Boötis

β Boötis

A star chart showing the position of β Eridani (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]
Characteristics
Spectral type G8IIIa[3]
U−B color index +0.75[2]
B−V color index +0.94[2]
Variable type Flare star
Astrometry
Radial velocity (Rv) –18.35[4] 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)
Details
Mass 3.4 ± 0.2[5] M☉
Radius 21.5 ± 1.0[5] R☉
Surface gravity (log g) 2.40 ± 0.20[5]
Luminosity 170[4] L☉
Temperature 4,932[4] K
Metallicity [Fe/H] –0.13[4] dex
Rotation 200 ± 10 days[5]
Rotational velocity (v sin i) 4.10 ± 1.0[5] km/s
Age 2.4 × 108[5] years
Other designations
Nakkar, Nekkar, Merez, Meres, Merets, 42 Boötis, HR 5602, HD 133208, BD+40°2840, FK5 555, HIP 73555, SAO 45337, GC 20226.[3]

Beta Boötis (β Boo, β Boötis) is a variable star in the constellation Boötes. It is a yellow G-type giant with an apparent magnitude of +3.49. The traditional name Nakkar or Nekkar is based upon the Arabic name for the constellation.[6] 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. In the modern constellation, it marks the head of Boötis the herdsman.[6] This star is approximately 225 light years from Earth.

This star has more than three times the mass of the Sun and greater than 21 times the Sun's radius. The estimated age is 240 million years, which is oddly younger than the expected age of a post-main sequence, giant star of this mass. The reason for this discrepancy is unexplained. It has an estimated rotation period of about 200 days and is inclined 28° ± 6° to the line of sight from the Earth.[5] 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.[7]

References

  1. ^ a b c d e van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c 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 "bet Boo -- Flare Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=beta+bootis, retrieved 2011-11-28 
  4. ^ a b c d 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 
  5. ^ a b c d e f g 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, Bibcode 2006MNRAS.365.1050K, doi:10.1111/j.1365-2966.2005.09796.x 
  6. ^ a b Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 103, http://books.google.com/books?id=5xQuAAAAIAAJ&pg=RA103, retrieved 2011-11-28 
  7. ^ 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 

External links

Stars of Boötes
Bayer
Flamsteed
Nearby
  • Wolf 498
  • ξ
  • SDSS J1416+13