Beta Boötis, Latinized from β Boötis, and also named Nekkar /ˈnɛkɑːr/,[10] 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.[11] Based upon parallax measurements obtained by the Gaia spacecraft, this star is approximately 235 light-years (72 parsecs) from the Sun.[1] The magnitude of the star is reduced by 0.06 from extinction caused by intervening gas and dust.[6]
  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Boötes |
| Right ascension | 15h 01m 56.7623s[1] |
| Declination | +40° 23′ 26.0469″[1] |
| Apparent magnitude (V) | 3.488[2] |
| Characteristics | |
| Evolutionary stage | Yellow giant |
| 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: –40.708 mas/yr[1] Dec.: –30.168 mas/yr[1] |
| Parallax (π) | 13.878 ± 0.131 mas[1] |
| Distance | 235 ± 2 ly (72.1 ± 0.7 pc) |
| Absolute magnitude (MV) | –0.70[6] |
| Details | |
| Mass | 3.23±0.07[7] M☉ |
| Radius | 18.44±0.19[8] R☉ |
| Luminosity | 188±10[8] L☉ |
| Surface gravity (log g) | 2.45±0.03[7] cgs |
| Temperature | 4,997[9] K |
| Metallicity [Fe/H] | –0.086[9] dex |
| Rotation | 200±10[4] days |
| Rotational velocity (v sin i) | 4.1±1.0[4] km/s |
| Age | 320±20[7] Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Nomenclature
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'.[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] 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 included in the List of IAU-approved Star Names.[10]
Properties
This star had its angular diameter measured using interferometric observations by the Navy Precision Optical Interferometer. The angular diameter, together with the star's distance, yield a radius 18 times the radius of the Sun.[8] Beta Boötis is 3.2 times more massive than the Sun. At the estimated age of 320 million years,[7] it has evolved into a giant star with a stellar classification of G8 IIIa.[3] The star is radiating around 188[8] times as much luminosity as the Sun from its outer envelope at an effective temperature of 5,000 K.[9] 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.[13]
References
External links
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