Alioth

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For other uses, see Alioth (disambiguation).
Alioth
Location of Alioth (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 12h 54m 01.74959s[1]
Declination +55° 57′ 35.3627″[1]
Apparent magnitude (V) 1.77[2]
Characteristics
Spectral type A1III-IVp kB9
U−B color index +0.02[2]
B−V color index −0.02[2]
Variable type
α2 CVn
Distance
82.6 ± 0.4 ly
(25.3 ± 0.1 pc)
Absolute magnitude (MV)−0.2[4]
Details
Myr
PPM
 33769
Database references
SIMBADdata

Alioth /ˈæliɒθ/, also called Epsilon Ursae Majoris, is a star in the northern constellation of Ursa Major. The designation is Latinised from ε Ursae Majoris and abbreviated Epsilon UMa or ε UMa.[11][12] Despite being designated "ε" (epsilon), it is the brightest star in the constellation and at magnitude 1.77 is the thirty-third brightest star in the sky.

It is the star in the tail of the bear closest to its body, and thus the star in the handle of the

navigational stars.[1]

Physical characteristics

Book plate by Sidney Hall depicting Ursa Major's stars
A light curve for Epsilon Ursae Majoris, plotted from TESS data[13]

According to

spectrum is characteristic of an α2 Canum Venaticorum variable. Epsilon Ursae Majoris, as a representative of this type, may harbor two interacting processes. First, the star's strong magnetic field separating different elements in the star's hydrogen 'fuel'. In addition, a rotation axis at an angle to the magnetic axis may be spinning different bands of magnetically sorted elements into the line of sight between Epsilon Ursae Majoris and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Epsilon Ursae Majoris to have very strange spectral lines that fluctuate over a period of 5.1 days. The kB9 suffix to the spectral type indicates that the calcium
K line is present and representative of a B9 spectral type even though the rest of the spectrum indicates A1.

Epsilon Ursae Majoris's rotational and magnetic poles are at almost 90 degrees to one another. Darker (denser) regions of chromium form a band at right angles to the equator.

It has long been suspected that Epsilon Ursae Majoris is a

spectroscopic binary, possibly with more than one companion.[14] A more recent study suggests Epsilon Ursae Majoris's 5.1-day variation may be due to a substellar object of about 14.7 Jupiter masses in an eccentric orbit (e=0.5) with an average separation of 0.055 astronomical units.[15] It is now thought that the 5.1-day period is the rotation period of the star, and no companions have been detected using the most modern equipment.[6]

Epsilon Ursae Majoris has a relatively weak magnetic field, 15 times weaker than α Canum Venaticorum, but it is still 100 times stronger than that of the Earth.[16]

Name and etymology

ε Ursae Majoris (Latinised to Epsilon Ursae Majoris) is the star's Bayer designation.

The traditional name Alioth comes from the Arabic alyat al-hamal ("the sheep's fat tail"). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[18] included a table of the first two batches of names approved by the WGSN; which included Alioth for this star.

This star was known to the

Seven Rishis.[19]

In

Chinese name for Epsilon Ursae Majoris itself is 北斗五 (Běi Dǒu wu, English: the Fifth Star of Northern Dipper) and 玉衡 (Yù Héng, English: Star of Jade Sighting-Tube).[20]

Namesakes

The

Crater class cargo ship USS Allioth (AK-109)
was named after the star.

See also

References

  1. ^
    S2CID 18759600
  2. ^
    Bibcode:1966CoLPL...4...99J
    .
  3. Bibcode:1967IAUS...30...57E
  4. ^
    S2CID 122817347
  5. S2CID 119226823
  6. ^
    S2CID 96452769
    .
  7. S2CID 119298606
    .
  8. ^
    S2CID 119417105
    .
  9. S2CID 14070763
  10. doi:10.1088/0004-6256/143/1/2
    .
  11. ISBN 978-1-931559-44-7
    .
  12. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  13. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  14. doi:10.1093/mnras/183.4.701
    .
  15. S2CID 17104356
    .
  16. S2CID 119070948
    .
  17. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  18. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Archived (PDF) from the original on 2022-10-09. Retrieved 28 July 2016.
  19. ISBN 0-486-21079-0
    . Retrieved 2012-09-04.
  20. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日
  1. ^ Public Domain This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "Allioth". Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al.
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