Dubhe

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Template:Short description

Template:Starbox visbin

Dubhe
Template:Location mark
Location of Dubhe (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Pronunciation Template:IPAc-en
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 1.79[2] (1.87 + 4.85)[3]
Characteristics
Spectral type K0III[4] + A5V[3]
U−B Template:Engvar +0.93[2]
B−V Template:Engvar +1.07[2]
Variable type Suspected[5]
Astrometry
Radial velocity (Rv)Template:Val[6] km/s
Proper motion (μ) RA: –134.11[1] mas/yr
Dec.: –34.70[1] mas/yr
Parallax (π)26.54±0.48 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)Template:Val[7]
Details
α UMa A
MassTemplate:Val[3] Template:Solar mass
RadiusTemplate:Val[8] Template:Solar radius
Luminosity339[9] Template:Solar luminosity
Surface gravity (log g)2.22[3] cgs
TemperatureTemplate:Val[8] K
Metallicity [Fe/H]–0.15[3] dex
Rotation<1.35[3] years
Rotational velocity (v sin i)Template:Val[3] km/s
AgeTemplate:Val[10] Myr
α UMa B
MassTemplate:Val[3] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[11]
Database references
SIMBADdata

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Dubhe is a multiple star system in the northern constellation of Ursa Major. It is formally designated Alpha Ursae Majoris, Latinised from α Ursae Majoris,[12][13] Despite being designated "α" (alpha), it is the second-brightest object in the constellation. Alpha Ursae Majoris is the northern of the 'pointers' (or 'guards'), the second being Beta Ursae Majoris, or 'Merak' – this pair of stars point towards Polaris, the North Star.[14] α Ursae Majoris is located at a distance of approximately 123 light years from the Sun, based on parallax measurements.

Although it is part of the constellation of Ursa Major, it is not part of the Ursa Major Moving Group of stars that have a common motion through space.[15]

Components

Dubhe A & B
α Ursae Majoris A and faint companion binaries

Dubhe is a spectroscopic binary made up of the stars α Ursae Majoris A and α Ursae Majoris B. The pair orbit at a separation of about 23 astronomical units (AU),[16] with a period of 44.5 years and an eccentricity of 0.44.[3] There is another spectroscopic binary at an angular separation of 7.1 arcminutes, forming a 7th magnitude pair showing an F8 spectral type with an orbital period of 6.035 days and an eccentricity of 0.09. It is sometimes referred to as Alpha Ursae Majoris C, but is separately catalogued as HD 95638.[16] Together they form a quadruple star system.[17]

File:Updated Hertzsprung-Russell Diagram.jpg
A Hertzsprung–Russell diagram showing the position of Dubhe on the red-giant branch

Component A is the system's primary, and it has a stellar classification of K0III.[4] This is a giant star that has evolved away from the main sequence after consuming the hydrogen at its core. It is 280 million years old[10] with 3.7 times the Sun's mass[3] and has expanded 27 times the radius of the Sun.[8] The star is radiating 340 times the luminosity of the Sun from its enlarged photosphere[9] at an effective temperature of Template:Val.[8] The secondary star, component B, is an A-type main-sequence star that has a class of A5V.[3] α Ursae Majoris has been reported to vary in brightness by about a thousandth of a magnitude. Ten radial oscillation modes have been detected, with periods between 6.4 hours and 6.4 days.[18]

In addition to the inner pair, a widely-separated star has been reported as having similar proper motions with Dubhe, and thus may form a gravitationally bound system. However, the chance of it being unrelated is around 40%, leaving its membership to Dubhe uncertain.[19]

Nomenclature

α Ursae Majoris (Latinised to Alpha Ursae Majoris) is the star system's Bayer designation.

It bore the traditional name Dubhe, which is derived from the Arabic for 'bear', Template:Transliteration, from the phrase Script error: No such module "Lang"., Template:Transliteration 'the back of the Greater Bear'. The ancient Egyptians called it Ak, meaning 'The Eye'.[20] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[21] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[22] included a table of the first two batches of names approved by the WGSN; which included Dubhe for the star α Ursae Majoris A.

The Hindus refer to the star as Kratu, one of the Seven Rishis.[20]

In Chinese, Script error: No such module "Lang". Běi Dǒu, meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Alpha Ursae Majoris itself is Script error: No such module "Lang". Běi Dǒu yī, (Template:Langx) and Script error: No such module "Lang". Tiān Shū, (Template:Langx).[23]

In culture

Dubhe is the official star of the State of Utah.[24]

Dubhe was a ship in the United States Navy. The Danish National Home Guard Navy ship MHV806 is also named Dubhe.

See also

References

Template:Reflist

Template:Sky Template:Stars of Ursa Major Template:Portal bar

  1. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named aaa474_2_653
  2. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named clpl4_99
  3. ↑ a b c d e f g h i j k Cite error: Invalid <ref> tag; no text was provided for refs named Gray2018
  4. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named guenther
  5. ↑ Script error: No such module "Citation/CS1".
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Gontcharov2006
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aj135_3_892
  8. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named Baines2025
  9. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Luck2015
  10. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named Baines_et_al_2017
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named SIMBAD
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Kunitzsch
  13. ↑ Script error: No such module "citation/CS1".
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Streicher2009
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named msc
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Eggleton_Tokovinin_2008
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named buzasi
  19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Kervella2022
  20. ↑ a b Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ Script error: No such module "citation/CS1".
  23. ↑ Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日 Template:Webarchive
  24. ↑ Script error: No such module "citation/CS1".
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