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]
Characteristics
Spectral type G8IIIa[3]
U−B color index +0.75[2]
B−V color index +0.94[2]
Variable type Flare star[4]
Astrometry
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]
Details
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]

References

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External links