Xi Ursae Majoris
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(Redirected from Alula Australis)
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Ursa Major |
| Right ascension | 11h 18m 11.0s |
| Declination | +31° 31′ 45″ |
| Apparent magnitude (V) | 3.79 (4.32/4.84) |
| Characteristics | |
| Spectral type | G0 Ve/G0 Ve |
| U−B color index | 0.04 |
| B−V color index | 0.59 |
| Variable type | ? |
| Astrometry | |
| Radial velocity (Rv) | -15.0 km/s |
| Proper motion (μ) | RA: -429 mas/yr Dec.: -587 mas/yr |
| Parallax (π) | 113.20 ± 4.60[1] mas |
| Distance | 29 ± 1 ly (8.8 ± 0.4 pc) |
| Absolute magnitude (MV) | 4.71/5.23 |
| Details | |
| Mass | 1.05/0.90 M☉ |
| Radius | 1.01/0.78 R☉ |
| Luminosity | 1.1/0.67 L☉ |
| Temperature | ~5,900/5,900 K |
| Metallicity | 0.98/0.76 |
| Rotation | 3 km/s |
| Age | 6 × 109 years |
| Orbit[2] | |
| Companion | ξ UMa A |
| Period (P) | 59.878 yr |
| Semimajor axis (a) | 2.536" |
| Eccentricity (e) | 0.398 |
| Inclination (i) | 127.94° |
| Longitude of the node (Ω) | 101.85 (ascending)° |
| Periastron epoch (T) | 1935.195 |
| Other designations | |
Xi Ursae Majoris (ξ UMa, ξ Ursae Majoris) is a star system in the constellation Ursa Major. On May 2, 1780, Sir William Herschel discovered that this was a binary star system, making it the first such system ever discovered. It was the first visual double star for which an orbit was calculated, when it was computed by Félix Savary in 1828.
The two components are yellow G-type main sequence dwarfs. The brighter component, Xi Ursae Majoris A, has a mean apparent magnitude of +4.41. It is classified as an RS Canum Venaticorum type variable star and its brightness varies by 0.01 magnitudes. The companion star, Xi Ursae Majoris B has an apparent magnitude of +4.87. The orbital period of the two stars is 59.84 years, and they are currently separated by 1.2 arcseconds, or at least 10 AUs.
Each component of this double star is itself a spectroscopic binary. B's binary companion, denoted Xi Ursae Majoris Bb, is unresolved, but the binary star is known to have an orbital period of 3.98 days. The masses of both A and B's companions (Ab and Bb) (deduced by the sum total mass of the system minus the likely masses of Aa and Ba determined by their class) indicate that they are probably MV stars (red dwarfs), Bb being on the cool end of the M spectrum, not much hotter than a brown dwarf. [3]
It also has the proper name Alula Australis[4] (and erroneously Alula Australe[5]) meaning "the Southern (star) of Alula." The words Alula, El Acola[6][7] and el-awla[8] (with ν) come from the Arabic phrase (al-Qafzah) al-Ūlā meaning "the first (leap)" (plus "Australis", "southern" in Latin).
It and Nu Ursae Majoris are Hea Tae （下台）, the Lower Dignitary, in Chinese astronomy.[9]
[edit] Notes
- ^ Karataş, Y.; Bilir, S.; Eker, Z.; Demircan, O. (April 2004), "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution", Monthly Notices of the Royal Astronomical Society 349 (3): 1069–1092, arXiv:astro-ph/0404219, Bibcode 2004MNRAS.349.1069K, doi:10.1111/j.1365-2966.2004.07588.x
- ^ Mason, Brian D.; McAlister, Harold A.; Hartkopf, William I. (January 1995), "Binary star orbits from speckle interferometry. 7: The multiple system XI Ursae Majoris", The Astronomical Journal 109 (1669): 332–340, Bibcode 1995AJ....109..332M, doi:10.1086/117277
- ^ http://www.astro.illinois.edu/~jkaler/sow/alulaaus.html
- ^ Piazzi, G., The Palermo Catalogue, Palermo, 1814.
- ^ Bečvář, A., Atlas Coeli (Atlas of the Heavens) II - Catalogue, Plague, 1964.
- ^ Burritt, E. H., Atlas, Designed to Illustrate the Geography of the Heavens, New York, 1835.
- ^ Funck & Wagenall, New Standard Dictionary of the English Language, New York & London, 1947.
- ^ Bode J., Uranographia, Berlin, 1801.
- ^ Allen, Richard Hinckley (1899). Star-Names and Their Meanings. New York: G. E. Stechert., p.443.
[edit] External links
- Animation of the orbits of the stars in the Alula Australis System at SolStation.com
- Main Article on Alula Australis at SolStation.com
- Alula Australis by Dr. Jim Kaler.
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