}}|caption=The red circle shows the location of Xi Ursae Majoris in Ursa Major }}
{{Starbox observe 2s
}}{{Starbox astrometry|no_heading=y
| component1=ξ UMa Aa
| absmag_bol=4.54 ± 0.06[15]
| absmag_v=4.66[7]
| component2=ξ UMa Ba
| absmag_bol2=5.00 ± 0.06[15]
| absmag_v2=5.16[8]
}}{{Starbox orbit
| reference =[19]
| primary=ξ UMa A
| name=ξ UMa B
| period=59.878
| axis=2.536
| eccentricity=0.398
| inclination=127.94
| node=101.85 (ascending)
| periastron=1935.195
}}{{Starbox orbit
| reference =[19]
| primary=ξ UMa B
| period=1.832
| axis=0.057
| eccentricity=0.53
| inclination=94.9
}}{{Starbox detail
|source=[9]
|component1=ξ UMa Aa
|temperature=6005 ± 80
|gravity=4.39 ± 0.10
|metallicity=−0.33 ± 0.07
|rotational_velocity=1.0 ± 1.0
|mass=0.97
|radius=1.02 ± 0.04
|component2=ξ UMa Ab
|mass2=0.38 ± 0.02
|radius2=0.32
|temperature2=∼3700[10]
}}{{Starbox detail|no_heading=y
|source=[9]
|component1=ξ UMa Ba
|temperature=5692 ± 90
|gravity=4.46 ± 0.10
|metal_fe=−0.35 ± 0.08
|rotational_velocity=3.0 ± 1.0
|mass=0.86
|radius=0.92 ± 0.04
|component2=ξ UMa Bb
|mass2={{val|0.14|-0.05|+0.09}}
}}{{Starbox catalog
| names=Alula Australis, ξ Ursae Majoris, ξ UMa, Xi UMa, 53 Ursae Majoris, BD+32°2132, CCDM J11182+3132, GC 15537, HIP 55203, IDS 11128+3206, SAO 62484, WDS J11182+3132
| component1 = A
| names1=HD 98231, HR 4375
| component2 = B
| names2=HD 98230, HR 4374
}}{{Starbox reference
|Simbad=**+WTE+1|sn=ξ UMa
|Simbad2=*+ksi+UMa|sn2=ξ UMa AB
|Simbad3=TYC+2520-2634-1|sn3=ξ UMa A
|Simbad4=TYC+2520-2634-2|sn4=ξ UMa B
|Simbad5=HD+98230b|sn5=ξ UMa Bb
|Simbad6=2MASS+J11183876%2b3125441|sn6=WISE J1118+3125
}}{{Starbox end}}Xi Ursae Majoris (ξ Ursae Majoris, abbreviated Xi UMa, ξ UMa), also named Alula Australis,[11] is a star system in the constellation of 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. It is also a variable star with a small amplitude. Xi Ursae Majoris is found in the left hind paw of the Great Bear.[12]Stellar system
The two components are yellow main sequence stars. The brighter component (designated Xi Ursae Majoris A), has a mean apparent magnitude of +4.41. 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 AU.
Each component of this double star is itself a single-lined spectroscopic binary. The orbit of the A pair has been determined from spectroscopy and speckle interferometry, giving a period of 669 days and an eccentricity of 0.53.[19] B's binary companion (Xi Ursae Majoris Bb)has not been detected visually or spectroscopically, but the radial velocity variations of the spectral lines show a circular orbit with a period of 3.98 days.[13] 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 red dwarfs, Bb being on the cool end of the M spectrum, not much hotter than a brown dwarf.[14]
In 2012 Wright et al. discovered the fifth component and the second brown dwarf (if Bb is also a brown dwarf) of the system using Wide-field Infrared Survey Explorer (WISE) data—a T8.5 brown dwarf WISE J111838.70+312537.9 with angular separation 8.5 arc-min, and the projected physical separation about 4000 AU.{{r|Wright2012}}
Variable star
ξ Ursae Majoris is classified as an RS Canum Venaticorum variable and its brightness varies by 0.01 magnitudes.[15] Component B is believed to be the variable star, showing characteristic emission lines in its spectrum that are not present for component A.[16]
Nomenclature
ξ Ursae Majoris (Latinised to Xi Ursae Majoris) is the star's Bayer designation.
It also bore the traditional names Alula Australis[17] (and erroneously Alula Australe[18]). Alula (shared with Nu Ursae Majoris) comes from the Arabic phrase {{transl|ar|Al Ḳafzah al Ūla}} 'the First Spring'[19] and Australis is Latin for 'the south side'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[20] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[21] included a table of the first two batches of names approved by the WGSN; which included Alula Australis for this star.
In Chinese, {{lang|zh|三台}} ({{lang|zh-Latn|Sān Tái}}), meaning Three Steps, refers to an asterism consisting of Xi Ursae Majoris, Iota Ursae Majoris, Kappa Ursae Majoris, Lambda Ursae Majoris, Mu Ursae Majoris and Nu Ursae Majoris. Consequently, Xi Ursae Majoris itself is known as {{lang|zh|下台二}} ({{lang|zh-Latn|Xià Tái èr}}, {{lang-en|Star of Second Lower Step}}).[22]
See also
- List of star systems within 25–30 light-years
References
1. ^1 2 3 4 5 {{cite journal|title=The Tycho-2 catalogue of the 2.5 million brightest stars|author=Høg, E.|display-authors=etal|date=2000|journal=Astronomy and Astrophysics|volume=355|pages=L27–L30|bibcode=2000A&A...355L..27H}}
2. ^{{cite journal|bibcode=1989ApJS...71..245K|title=The Perkins catalog of revised MK types for the cooler stars|journal=Astrophysical Journal Supplement Series|volume=71|pages=245|author1=Keenan|first1=Philip C|last2=McNeil|first2=Raymond C|year=1989|doi=10.1086/191373}}
3. ^1 {{cite journal|bibcode=1978A&AS...34....1N|title=Catalogue of homogeneous data in the UBV photoelectric photometric system|journal=Astronomy and Astrophysics|volume=34|pages=1|author1=Nicolet|first1=B|year=1978}}
4. ^{{cite journal|bibcode=1993ApJS...86..599D|title=The ROSAT All-Sky Survey of active binary coronae. I - Quiescent fluxes for the RS Canum Venaticorum systems|journal=Astrophysical Journal Supplement Series|volume=86|pages=599|author1=Dempsey|first1=Robert C|last2=Linsky|first2=Jeffrey L|last3=Fleming|first3=Thomas A|last4=Schmitt|first4=J. H. M. M|year=1993|doi=10.1086/191791}}
5. ^{{cite journal|title=The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ~{{val|14000}} F and G dwarfs|author=Nordström, B.|display-authors=etal|journal=Astronomy and Astrophysics|volume=418|issue=3|pages=989–1019|date=2004|bibcode=2004A&A...418..989N|doi=10.1051/0004-6361:20035959|arxiv=astro-ph/0405198}}
6. ^1 {{cite journal|author1=Zacharias, N.|title=The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4)|journal=VizieR On-line Data Catalog|volume=1322|date=2012|bibcode=2012yCat.1322....0Z}}
7. ^Calculated from the bolometric magnitude 4.54 ± 0.06 and the bolometric correction −0.12 ± 0.05 using the formula: BC = Mbol − MV
8. ^Calculated from the bolometric magnitude 5.00 ± 0.06 and the bolometric correction −0.16 ± 0.05 using the formula: BC = Mbol − MV
9. ^1 2 3 {{cite journal|title=Nearby stars of the Galactic disc and halo - IV|author=Fuhrmann, Klaus|journal=Monthly Notices of the Royal Astronomical Society|volume=384|issue=1|pages=173–224|date=2008|bibcode=2008MNRAS.384..173F|doi=10.1111/j.1365-2966.2007.12671.x}}
10. ^This estimates assumes that ξ UMa Ab is a red dwarf.
11. ^{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |accessdate=28 July 2016}}
12. ^Spectroscopic binary orbits from photoelectric radial velocities. Paper 142: Xi Ursae Majoris page 274
13. ^{{cite journal|bibcode=1931LicOB..15..109B|title=The spectroscopic orbit of the fainter component in the system [xi] Ursae Majoris|journal=Lick Observatory bulletin ; no. 432; Lick Observatory bulletins ; no. 432|volume=15|pages=109|author1=Berman|first1=Louis|year=1931|doi=10.5479/ADS/bib/1931LicOB.15.109B}}
14. ^{{cite web|url=http://www.astro.illinois.edu/~jkaler/sow/alulaaus.html |title=Archived copy |accessdate=June 29, 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20110716072201/http://www.astro.illinois.edu/~jkaler/sow/alulaaus.html |archivedate=July 16, 2011 }}{{Dead link|date=July 2018}}
15. ^{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S|volume=1|display-authors=etal|author1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}
16. ^{{cite journal|bibcode=1989ApJS...69..141S|title=Photometric variability in chromospherically active stars. III - the binary stars|journal=Astrophysical Journal Supplement Series|volume=69|pages=141|author1=Strassmeier|first1=Klaus G|last2=Hall|first2=Douglas S|last3=Boyd|first3=Louis J|last4=Genet|first4=Russell M|year=1989|doi=10.1086/191310}}
17. ^Piazzi, G., The Palermo Catalogue, Palermo, 1814.
18. ^Bečvář, A., Atlas Coeli (Atlas of the Heavens) II – Catalogue, Plague, 1964.
19. ^Richard Hinckley Allen :Star Names — Their Lore and Meaning – Ursa Major, the Greater Bear
20. ^{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|accessdate=22 May 2016}}
21. ^{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 1 |accessdate=28 July 2016}}
22. ^{{zh icon}} (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日
23. ^1 2 3 {{citation | last1=Mason | first1=Brian D. | last2=McAlister | first2=Harold A. | last3=Hartkopf | first3=William I. | last4=Shara | first4=M. M. | last5=Shara | first5=M. M. | title=Binary star orbits from speckle interferometry. 7: The multiple system XI Ursae Majoris | journal=The Astronomical Journal | volume=109 | issue=1669 | pages=332–340 |date=January 1995 | bibcode=1995AJ....109..332M |doi = 10.1086/117277 }}
24. ^{{cite arXiv|last=Wright |first=Edward L.|author2=Skrutskie, M. F.|author3=Kirkpatrick, J. Davy|author4=Gelino, Christopher R.|author5=Griffith, Roger L.|author6=Marsh, Kenneth A.|author7=Jarrett, Tom|author8=Nelson, M. J.|author9=Borish, H. J.|author10=Mace, Gregory|author11=Mainzer, Amanda K.|author12=Eisenhardt, Peter R.|author13=McLean, Ian S.|author14=Tobin, John J.|author15=Cushing, Michael C.|title=A T8.5 Brown Dwarf Member of the Xi Ursae Majoris System|date=2012|eprint=1203.5764v1|class=astro-ph.SR}}