Epsilon Ursae Majoris

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"Alioth" redirects here. For the free software development service, see Alioth (Debian).
Epsilon Ursae Majoris
Ursa Major constellation map.svg
Cercle rouge 100%.svg

Alioth in Ursa Major (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 A0pCr
U−B color index +0.02[2]
B−V color index -0.02[2]
Variable type α2-CVn
Astrometry
Radial velocity (Rv) -9.3[3] km/s
Proper motion (μ) RA: +111.91[1] mas/yr
Dec.: -8.24[1] mas/yr
Parallax (π) 39.51 ± 0.20[1] mas
Distance 82.6 ± 0.4 ly
(25.3 ± 0.1 pc)
Absolute magnitude (MV) –0.2[4]
Details
Mass 2.91[5] M
Radius 4.2 ± 0.2[6] R
Luminosity 108 L
Surface gravity (log g) 3.5[4] cgs
Temperature 10,800[4] K
Metallicity [Fe/H] +0.00[4] dex
Rotational velocity (v sin i) 33[7] km/s
Other designations
Alioth, Allioth, Aliath, ε Ursae Majoris, ε UMa, Epsilon UMa, 77 Ursae Majoris, BD+56°1627, FK5 483, GC 17518, HD 112185, HIP 62956, HR 4905, PPM 33769, SAO 28553.

Epsilon Ursae Majoris (Epsilon UMa, ε Ursae Majoris, ε UMa) is the brightest star in the constellation Ursa Major (despite its Bayer designation being merely "epsilon"), and at magnitude 1.76 is the thirty-first brightest star in the sky. It has the traditional name Alioth. It is the star in the tail of the bear closest to its body, and thus the star in the handle of the Big Dipper (Plough) closest to the bowl. It is also a member of the large and diffuse Ursa Major moving group. Historically, the star was frequently used in celestial navigation in the maritime trade, because it is listed as one of the 57 navigational stars.[1]

Peculiarities[edit]

Book plate by Sydney Hall depicting Ursa Major's stars

According to Hipparcos, Alioth is 81 light years (25 parsecs) from Earth. Its spectral type is A0p; the "p" stands for peculiar, as the spectrum of its light is characteristic of an Alpha2 Canum Venaticorum variable. Alioth, 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 Alioth and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Alioth to have very strange spectral lines that fluctuate over a period of 5.1 days.

With Alioth, the rotational and magnetic axes are at almost 90 degrees to one another. Darker (denser) regions of chromium form a band at right angles to the equator.

A recent study suggests Alioth'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.

Alioth has a relatively weak magnetic field, 15 times weaker than α CVn, but it is still 100 times stronger than that of the Earth.

Name and etymology[edit]

Namesakes[edit]

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

See also[edit]

References[edit]

  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c Johnson, H. L. et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory 4 (99). Bibcode:1966CoLPL...4...99J. 
  3. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  4. ^ a b c d Tektunali, H. G. (June 1981), "The spectrum of the CR star Epsilon Ursae Majoris", Astrophysics and Space Science 77 (1): 41–58, Bibcode:1981Ap&SS..77...41T, doi:10.1007/BF00648756 
  5. ^ Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement 192 (1): 2, arXiv:1007.0425, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2 
  6. ^ Sokolov, N. A. (March 2008), "Radial velocity study of the chemically peculiar star ɛ Ursae Majoris", Monthly Notices of the Royal Astronomical Society: Letters 385 (1): L1–L4, arXiv:0904.3562, Bibcode:2008MNRAS.385L...1S, doi:10.1111/j.1745-3933.2008.00419.x. 
  7. ^ Royer, F. et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943 
  8. ^ Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 438. ISBN 0-486-21079-0. Retrieved 2012-09-04. 
  9. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日
  1. ^  This article incorporates text from a publication now in the public domainChambers, Ephraim, ed. (1728). "article name needed". Cyclopædia, or an Universal Dictionary of Arts and Sciences (first ed.). James and John Knapton, et al.