Xi Ursae Majoris

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Template:Short description

Xi Ursae Majoris
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The red circle shows the location of Xi Ursae Majoris in Ursa Major.
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Pronunciation Template:IPAc-en[1]
ξ UMa A
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 4.264[2]
ξ UMa B
Right ascension Template:RA[2]
Declination Template:DEC[2]
Apparent magnitude (V) 4.729[2]
Characteristics
Spectral type F8.5:V / G2V[3]
U−B Template:Engvar 0.04[4]
B−V Template:Engvar 0.59[4]
Variable type RS CVn[5]
Astrometry
Radial velocity (Rv)Template:Val[6] km/s
Proper motion (μ) RA: −339.398 mas/yr[7]
Dec.: −607.892 mas/yr[7]
Parallax (π)114.4867±0.4316 mas[7]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
ξ UMa Aa
Absolute magnitude (MV)4.66[note 1]
Absolute bolometric
magnitude (Mbol)		Template:Val[8]
ξ UMa Ba
Absolute magnitude (MV)5.16[note 2]
Absolute bolometric
magnitude (Mbol)		Template:Val[8]
Orbit[9]
Primaryξ UMa A
Companionξ UMa B
Period (P)59.878 yr
Semi-major 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
Orbit[9]
Primaryξ UMa Aa
Companionξ UMa Ab
Period (P)1.832 yr
Semi-major axis (a)0.057″
Eccentricity (e)0.53
Inclination (i)94.9°
Details[8]
ξ UMa Aa
Mass0.97 Template:Solar mass
RadiusTemplate:Val Template:Solar radius
Luminosity1.21 Template:Solar luminosity
Surface gravity (log g)Template:Val cgs
TemperatureTemplate:Val K
Rotational velocity (v sin i)Template:Val km/s
ξ UMa Ab
MassTemplate:Val Template:Solar mass
Radius0.32 Template:Solar radius
Temperature~3,700[note 3] K
Metallicity [Fe/H]{{{metal_fe2}}} dex
ξ UMa Ba
Mass0.86 Template:Solar mass
RadiusTemplate:Val Template:Solar radius
Luminosity0.79 Template:Solar luminosity
Surface gravity (log g)Template:Val cgs
TemperatureTemplate:Val K
Metallicity [Fe/H]Template:Val dex
Rotational velocity (v sin i)Template:Val km/s
ξ UMa Bb
MassTemplate:Val Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist
A: Template:Odlist
B: Template:Odlist
E: Template:Odlist
Database references
SIMBADξ UMa
ξ UMa AB
ξ UMa A
ξ UMa B
ξ UMa Bb
WISE J1118+3125

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Xi Ursae Majoris is a quintuple star system Template:Convert away in the constellation of Ursa Major. It has the traditional name Alula Australis;[1][10] Xi Ursae Majoris is the Bayer designation, which is Latinised from ξ Ursae Majoris and abbreviated Xi UMa or ξ UMa. It is a variable star with a small amplitude. Xi Ursae Majoris is found in the left hind paw of the Great Bear.[11]

Xi Ursae Majoris is the second-nearest quintuple system, after V1054 Ophiuchi.[12]

History of observations

Xi Ursae Majoris was found to be a visual double star by William Herschel in 1780,[13] and in 1804 he presented it as a likely physical binary star based on observed orbital motion.[14]Template:Rp It then became the first visual double star for which an orbit was calculated, when it was computed by Félix Savary in 1828.[13]

Stellar system

File:Xi UMa orbit.gif
Orbit of Xi Ursae Majoris

The two main 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. They are currently (2022) separated by 2.3 arcseconds, and will widen to a maximum 3.0 arcseconds in 2035.

File:Alula Australis - STF1523AB - HIP 55203.jpg
Double star Xi Ursae Majoris.(θ):156.6° (ρ):2.1 arc"

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.[9] B's binary companion (Xi Ursae Majoris Bb) has not been detected visually, but the radial velocity variations of the spectral lines show a circular orbit with a period of 3.98 days.[15] 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.[16] However, component Ba has been found to be enriched in barium relative to component Aa, suggesting that its companion Bb may be a white dwarf.[17]

In 2012 Wright et al. discovered the fifth component and the first 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 arcmin, and the projected physical separation about 4,000 AU.Template:R

Variable star

File:XiUMaLightCurve.png
A light curve for Xi Ursae Majoris, plotted from TESS data[18]

ξ Ursae Majoris is classified as an RS Canum Venaticorum variable and its brightness varies by 0.01 magnitude.[19] Component B is believed to be the variable star, showing characteristic emission lines in its spectrum that are not present for component A.[20]

Nomenclature

ξ Ursae Majoris (Latinised to Xi Ursae Majoris) is the star's Bayer designation.

It also bore the traditional names Alula Australis[21] (and erroneously Alula Australe[22]). Alula (shared with Nu Ursae Majoris) comes from the Arabic phrase Template:Transliteration 'the First Spring'[23] and Australis is Latin for 'southern'. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[24] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[25] included a table of the first two batches of names approved by the WGSN; which included Alula Australis for this star.

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), 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, the Chinese name for Xi Ursae Majoris itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx).[26]

See also

References

Template:Reflist

Note

Template:Reflist

External links

Template:Stars of Ursa Major

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  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Herschel1804
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  26. ↑ Template:In lang (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 21 日 Template:Webarchive


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