Beta Boötis
| 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 | |
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
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 3.0 3.1 3.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 7.0 7.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
