Alcor (star)

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Template:Short description

Template:Starbox catalogue

Alcor
Template:Location mark
Location of Alcor (Mizar is circled, Alcor is invisible beside it at this scale.)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) +3.99[2]
Characteristics
Spectral type A5Vn[3] / M3-4[4]
Astrometry
Radial velocity (Rv)−9.6[5] km/s
Proper motion (μ) RA: +120.21 mas/yr[1]
Dec.: Template:Val mas/yr[1]
Parallax (π)39.91±0.13 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)+2.00[2]
Details[6]
Alcor A
MassTemplate:Val Template:Solar mass
RadiusTemplate:Val (equatorial)
Template:Val (polar) Template:Solar radius
LuminosityTemplate:Val Template:Solar luminosity
Surface gravity (log g)4.25[7] cgs
TemperatureTemplate:Val (equator)
Template:Val (polar) K
Rotational velocity (v sin i)Template:Val km/s
AgeTemplate:Val Myr
Alcor B
Mass0.25[4] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
AgeTemplate:Val[2] Myr
Database references
SIMBADdata

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Alcor (Template:IPAc-en)[8] is a binary star system in the constellation of Ursa Major. It is the fainter companion of Mizar, the two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in Ursa Major. The two lie about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite.

Nomenclature

Alcor has the Flamsteed designation 80 Ursae Majoris. Alcor derives from Arabic Template:Large Script error: No such module "Lang"., meaning 'faint one';[9][10] notable as a faintly perceptible companion of Mizar.[11]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[13] included a table of the first two batches of names approved by the WGSN; which included Alcor for 80 UMa.[14]

Mizar and Alcor

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File:Dipper.jpg
Mizar and Alcor in constellation Ursa Major.

With normal eyesight magnitude 3.99 Alcor (spectral class A5V) appears at about 12 minutes of arc from the second-magnitude star Mizar.

Mizar's and Alcor's proper motions show they move together, along with most of the other stars of the Big Dipper except Dubhe and Alkaid, as members of the Ursa Major Moving Group, a mostly dispersed group of stars sharing a common birth. However, it has yet to be demonstrated conclusively that they are gravitationally bound. Recent studies indicate that Alcor and Mizar are somewhat closer together than previously thought: approximately 74,000 ± 39,000 AU, or 0.5–1.5 light-years. The uncertainty is due to our uncertainty about the exact distances from us. If they are exactly the same distance from us (somewhat unlikely) then the distance between them is only Template:Convert.[2]

Alcor B

File:BigdipISS.jpg
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.

In 2009, Alcor was discovered to have a companion star Alcor B, a magnitude 8.8 red dwarf.[15]

Alcor B was discovered independently by two groups. One group led by Eric Mamajek (University of Rochester) and colleagues at Steward Observatory University of Arizona used adaptive optics on the 6.5-meter telescope at MMT Observatory. Another led by Neil Zimmerman, a graduate student at Columbia University and member of Project 1640, an international collaborative team that includes astrophysicists at the American Museum of Natural History, the University of Cambridge's Institute of Astronomy, the California Institute of Technology, and NASA's Jet Propulsion Laboratory, used the 5-meter Hale Telescope at Palomar Observatory.[4]

Alcor B is one second of arc away from Alcor A.[4] Its spectral type is M3-4 and it is a main-sequence star, a red dwarf.

Alcor A and B are situated 1.2 light-years away from, and are co-moving with, the Mizar quadruple system, making the system the second-closest stellar sextuplet—only Castor is closer.[16] The Mizar–Alcor stellar sextuple system belongs to the Ursa Major Moving Group, a stellar group of stars of similar ages and velocities,[2] and the closest cluster-like object to Earth.

Other names

In Arabic, Alcor is also known as Al-Sahja (the rhythmical form of the usual al-Suhā) meaning "forgotten", "lost", or "neglected".[17]

In traditional Indian astronomy,[18] Alcor was known as Arundhati, wife of one of the Saptarishi.

In the Miꞌkmaq myth of the great bear and the seven hunters,[19] Mizar is Chickadee and Alcor is his cooking pot.

Military namesakes

USS Alcor (AD-34) and USS Alcor (AK-259) are both United States Navy ships.

References

Template:Reflist

External links

Template:Stars of Ursa Major Template:Sky

  1. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named hipparcos
  2. ↑ a b c d e Cite error: Invalid <ref> tag; no text was provided for refs named mamajek
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named gray
  4. ↑ a b c d Cite error: Invalid <ref> tag; no text was provided for refs named zimmerman
  5. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named kidger
  6. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named jones
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named david
  8. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Kunitzsch
  9. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named britannica
  10. ↑ List of Arabic star names, published in Popular Astronomy, January 1895, by Professor Robert H. West, of the Syrian Protestant College at Beirut.
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named bohigian
  12. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN
  13. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN1
  14. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named IAU-CSN
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named space.com
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named usatoday
  17. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named startales
  18. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named ref65zigip
  19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named micmac
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