Eta Ursae Majoris
 Alkaid in the Big Dipper of Ursa Major. |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Ursa Major |
| Right ascension | 13h 47m 32.43776s[1] |
| Declination | +49° 18′ 47.7602″[1] |
| Apparent magnitude (V) | +1.84[2] |
| Characteristics | |
| Spectral type | B3 V[3] |
| U−B color index | –0.68[2] |
| B−V color index | –0.18[2] |
| Astrometry | |
| Radial velocity (Rv) | –10.9[4] km/s |
| Proper motion (μ) | RA: –121.17[1] mas/yr Dec.: –14.91[1] mas/yr |
| Parallax (π) | 31.38 ± 0.24[1] mas |
| Distance | 103.9 ± 0.8 ly (31.9 ± 0.2 pc) |
| Details | |
| Mass | 6.1 ± 0.1[5] M☉ |
| Radius | 3.4[6] R☉ |
| Luminosity | 1,350[7] L☉ |
| Surface gravity (log g) | 4.27[8] |
| Temperature | 16,823 ± 177[6] K |
| Rotational velocity (v sin i) | 150[9] km/s |
| Age | 10.0 ± 2.6[5] Myr |
| Other designations | |
Eta Ursae Majoris (η UMa, η Ursae Majoris) is a star in the constellation Ursa Major. It has the traditional names Alkaid (or Elkeid) and Benetnash (Benetnasch). Alkaid is the most eastern (leftmost) star in the Big Dipper (Plough) asterism. However, unlike most stars of the Big Dipper, it is not a member of the Ursa Major moving group. With an apparent visual magnitude of +1.84,[2] it is the third brightest star in the constellation and one of the brightest stars in the night sky.
This is a 10 million year old[5] B-type main sequence star with a stellar classification of B3 V.[3] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[10] It has six[5] times the mass of the Sun and 3.4[6] times the Sun's radius. Eta Ursae Majoris is radiating around 1,350[7] times as much luminosity as the Sun from its outer atmosphere at an effective temperature of about 16,823 K,[6] giving it the blue-white hue of a B-type star.[11] This star is an X-ray emitter with a luminosity of 9.3 × 1028 erg s–1.[7]
[edit] In culture
The name derives from the Arabic phrase meaning "The leader of the daughters of the bier" (قائد بنات نعش qā'id bināt naʿsh). The daughters of the bier, i.e. the mourning maidens, are the three stars of the handle of the Big Dipper, Alkaid, Mizar, and Alioth; while the four stars of the bowl, Megrez, Phecda, Merak, and Dubhe, are the bier.
It is known as 北斗七 (the Seventh Star of the Northern Dipper) or 搖光 (the Star of Twinkling Brilliance) in Chinese.
In Japan, Alkaid in known as Hagunsei ("the military breaking star" or "most corner star"). Both meanings come from ancient China's influence in Japan. In Chinese fortune-telling, north is believe to be very unlucky direction. Northwest is even worse. Hunters and soldiers traditionally did not point guns and weapons in the direction of Hagunsei.[12]
USS Alkaid (AK-114) was a United States Navy Crater class cargo ship named after the star.
[edit] References
- ^ a b c d e van Leeuwen, Floor (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752v1, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357 Note: see VizieR catalogue I/311.
- ^ a b c d Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal 76: 1058, Bibcode 1971AJ.....76.1058C, doi:10.1086/111220
- ^ a b Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics 11: 29, Bibcode 1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333
- ^ Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b c d Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, Bibcode 2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x
- ^ a b c d Underhill, A. B. et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189: 601–605, Bibcode 1979MNRAS.189..601U
- ^ a b c Cassinelli, J. P. et al. (February 1994), "X-ray emission from near-main-sequence B stars", Astrophysical Journal, Part 1 421 (2): 705–717, Bibcode 1994ApJ...421..705C, doi:10.1086/173683
- ^ Niemczura, E. (June 2003), "Metallicities of the SPB stars from the IUE ultraviolet spectra", Astronomy and Astrophysics 404: 689–700, Bibcode 2003A&A...404..689N, doi:10.1051/0004-6361:20030546
- ^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal 573 (1): 359–365, Bibcode 2002ApJ...573..359A, doi:10.1086/340590
- ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode 1993AAS...183.1710G, http://www.astro.utoronto.ca/~garrison/mkstds.html, retrieved 2012-02-04
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ Littleton, C. Scott (2005), Gods, goddesses, and mythology, 11, New York: Marshall Cavendish Corporation, pp. 1338, http://books.google.com/books?id=guVGBE9t5igC
[edit] External links
- Alkaid at Jim Kaler's Stars website
