Alkor (star)

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Double star
Alkor (g Ursae Majoris)
Thomas Bresson - Mizar + alcor (by) .jpg
Mizar A and B (bottom left), Alkor (top right) and Sidus Ludoviciana (top left)
Location of Mizar (Alkor cannot be shown here)
Observation
dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation Big Bear
Apparent brightness  4.01 likes
Astrometry
Radial velocity −9.6 ± 1.0 km / s
parallax 39.91 ± 0.13 mas
distance  81.7 ± 0.3 ly
(25.06 ± 0.08 pc )
Proper movement :
Rec. Share: 120.21 ± 0.12 mas / a
Dec. portion: −16.4 ± 0.14 mas / a
orbit 
period about 100 years
Individual data
Names A; B.
Observation data:
Right ascension A. 13 h 25 m 13.54 s
B.
declination A. 2545916.7+ 54 ° 59 ′ 16.7 ″
B.
Apparent brightness A. 4.01 likes
B. > 8 likes
Typing:
Spectral class A. A5 Vn
B. M2 V - M3.5 V
B − V color index A. 0.17
U − B color index A. 0.09
Physical Properties:
Absolute vis.
Brightness M vis 		A. 2.00 ± 0.01 mag
B.
Dimensions A. 1.8 M ☉
B. 0.2 - 0.3 M ☉
Luminosity A. 12.9 ± 0.3 L ☉
B. 0.01 L ☉
Effective temperature A. 8,030 K
B. 3,437 K
Age 500 ± 100 million years
Other names
and catalog entries
Bayer name g Ursae Majoris
Flamsteed name 80 Ursae Majoris
Bonn survey BD + 55 ° 1603
Bright Star Catalog HR 5062 [1]
Henry Draper Catalog HD 116842 [2]
SAO catalog SAO 28751 [3]
Tycho catalog TYC 3850-1384-1 [4]
Hipparcos catalog HIP 65477 [5]
WDS catalog WDS 13239 + 5456
Further designations: PSF 1

Template: Infobox double star / maintenance / single coordinates

Alkor ( Bayer designation : g Ursae Majoris , short: g UMa), colloquially the “Little Rider” (in Southwest Germany also “Deichselreiter”) is a 4th magnitude star in the constellation of the Great Bear . It has an apparent magnitude of 4.0 m and is about 82 light years from the sun. Alkor is not a single star, but a binary star system that is also a member of the Ursa Major Cluster . To this day it is not clear whether the Alkor system forms a multiple star system with the neighboring Mizar system .

Location and observation

When the sky is clear, a good eye can recognize Alkor as a 4th magnitude star immediately north of Mizar, the center drawbar star of the Big Dipper ( see also: Eye tester ). The angular distance is 11 ′ 46.9 ″, the position angle is 70 ° (year 2013). As mentions in medieval Arabic sources show, the double star was known long before Galileo's often-cited telescope observations.

etymology

Traditionally the double star Mizar - Alkor is interpreted as "horse and rider", whereby Mizar represents the "horse" and Alkor the "rider" or the "little rider". So was the Latin name for Alkor Eques Stellula (roughly " little rider star "). The name Alkor very likely has the same origin as the name of the star Alioth (ε Ursae Majoris). Its Arabic name was El-dschaun (or from Ulugh Beg the name Al Haun is passed down), which means "the black horse" or "the black horse". According to JE Bode , the “dschaun” was corrupted into “hor” or “chor”, which ultimately reads “el-hor” / “el-chor” / “al-hor” / “with the article“ el ”or“ al ” al-chor "results. Bode suspected that the name was so unfortunate placed on an old Arabic star map between Alkor and Alioth that the name was henceforth added to Alkor instead of Alioth.

Apart from that, Alkor actually had an Arabic proper name, namely Suhā or El-suhā ("the forgotten", "the lost", "the neglected", this designation already indicates the weak brightness related to Mizar). Whoever looked to Suhā is said to have been preserved from snakes and scorpions according to an old Arab wisdom (narrated by Zakariya Qazwini ).

An old Greek legend tells that the Pleiade Elektra wandered into the Big Dipper and became Ἀλώπηξ ( Alōpēx , ancient Greek "fox").

According to an Indian idea, Mizar is a woman who carries a child (Alkor) on her back.

properties

The Alkor system consists of the main star Alkor A , a main sequence star of the spectral class A5 Vn, and Alkor B , a red dwarf star of the spectral class M2 V to M3.5 V. Since the Alkor system is a member of the Ursa major cluster, can it can be assumed that the star system is the same age as the cluster, namely 500 ± 100 million years. Alkor A has 1.8 solar masses and an effective surface temperature of 8,030 K . Its luminosity is around 13 times that of the sun.

Alkor is a candidate for a variable star with no more precise classification and is listed in the New Catalog of Suspected Variable Stars under the number NSV 6238. According to the Hipparcos mission , its apparent brightness fluctuates with an amplitude of 0.017 ± 0.006 m .

Alkor B

The discovery of Alkor B was made independently by two American teams of astronomers (Mamajek et al. And Zimmerman et al. ) And published in 2010. Alkor B was not detected in visible light, but in the mid-infrared (M-band, λ = 4.8 µm) on the MMT or in the near-infrared (H-band and J-band, λ = 1.10 - 1.76) µm) discovered at the Hale telescope ( see also: infrared astronomy ).

Alkor was previously recorded by the ROSAT satellite as an X-ray source with a luminosity of 10 28.3 erg / s and cataloged under the designations 1RXS J132513.8 + 545920 and 2RXP J1325.9 + 545914. Since A stars do not usually emit X-rays, this already indicated an undiscovered companion star. This discovery supports the assumption that the X-rays from other A stars (around 10 to 15% of all A stars were identified by ROSAT as X-ray sources) also originate from previously undiscovered, low-mass companion stars.

The apparent brightness of Alkor B is 7.58 ± 0.06 m in the H-band , 7.97 ± 0.06 m in the J-band and 8.82 ± 0.05 m in the M-band . Assuming a star age of 600 million years and a distance module of 2 m , based on the models for star evolution , this leads to a mass between 0.2 and 0.3 solar masses, a spectral class between M2 V and M3.5 V, an effective surface temperature of 3.437 K and a luminosity of 0.01 solar luminosity close.

The distance from Alkor B to Alkor A is 1.11 arc seconds , the position angle is 208.8 ° (observation from April 8, 2007). Assuming that this distance is equated with the major semi-axis of the orbit of Alkor B around Alkor A (which would correspond to 27.8 AU ), a circular orbit is assumed and Alkor A is 1.8 solar masses and Alkor B 0.3 Assuming solar masses, this would result in an orbital period of about a century.

Question of the togetherness of Mizar and Alkor

Trivia

After the star is u. a. named the research ship Alkor of the GEOMAR Helmholtz Institute for Ocean Research Kiel. The Bärenreiter-Verlag is also named after the star. The publisher's signature shows a star over a bear. The Alkor Edition, an agency for orchestral sheet music, is part of the Bärenreiter group of companies.

Web links

Individual evidence

  1. ↑ a b c T. Oja: VizieR Online Data Catalog: UBV Photometry of Stars with Accurate Positions (Oja 1984-1993). In: VizieR On-line Data Catalog: II / 182. (originally published in: bibcode : 1984A & AS ... 57..357O ; bibcode : 1985A & AS ... 59..461O ; bibcode : 1985A & AS ... 61..331O ; bibcode : 1986A & AS ... 65..405O ; bibcode : 1987A & AS ... 68..211O ; bibcode : 1987A & AS ... 71..561O ; bibcode : 1991A & AS ... 89..415O ; bibcode : 1993A & AS..100..591O ). 1996. bibcode : 1996yCat.2182 .... 0O . Corresponding database entry for Alkor on VizieR .
  2. ↑ a b B. D. Mason et al .: VizieR Online Data Catalog: The Washington Visual Double Star Catalog (Mason + 2001-2014) . Version 2016-04-18. In: VizieR On-line Data Catalog: B / wds. (originally published in: bibcode : 2001AJ .... 122.3466M ). 2016. bibcode : 2016yCat .... 102026M . Corresponding database entry for Mizar / Alkor and Alkor A / Alkor B on VizieR (WDS 13239 + 5456).
  3. ↑ GA Gontcharov: Vizier Online Data Catalog: Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006). In: VizieR On-line Data Catalog: III / 252. (originally published in: bibcode : 2006PAZh ... 32..844G ; bibcode : 2006AstL ... 32..759G ). 2007. bibcode : 2007yCat.3252 .... 0G . Corresponding database entry for Alkor on VizieR .
  4. ^ A b F. van Leeuwen: VizieR Online Data Catalog: Hipparcos, the New Reduction (van Leeuwen, 2007). In: VizieR On-line Data Catalog: I / 311. (originally published in: bibcode : 2007A & A ... 474..653V ). 2008. bibcode : 2008yCat.1311 .... 0V . Corresponding database entry for Alkor on VizieR .
  5. ↑ Derived from parallax (0.03991 ± 0.00013 ″ according to van Leeuwen, 2008).
  6. ↑ a b c d e f g h i j k l E. E. Mamajek et al: Discovery of a Faint Companion to Alcor Using MMT / AO 5 µm Imaging. In: The Astronomical Journal . Volume 139, Issue 3, 2010, pp. 919 ff. Bibcode : 2010AJ .... 139..919M . doi: 10.1088 / 0004-6256 / 139/3/919 . arxiv : 0911.5028 .
  7. ↑ a b c d e f E. Zimmermann et al .: Parallactic Motion for Companion Discovery: An M-Dwarf Orbiting Alcor. In: The Astrophysical Journal . Volume 709, Ed. 2, 2010, pp. 733 ff. Bibcode : 2010ApJ ... 709..733Z . doi: 10.1088 / 0004-637X / 709/2/733 . arxiv : 0912.1597 .
  8. ↑ a b c d e R. H. Allen: Star-Names and their Meanings . GE Stechert, New York / London / Leipzig / Paris 1899, pp. 439, 445, 446.
  9. ↑ a b c d J. E. Bode: Astronomical yearbook for the year 1808 . CFE Späthen, Berlin 1805, p. 107 f.
  10. ^ ESA: VizieR Online Data Catalog: The Hipparcos and Tycho Catalogs (ESA 1997). In: VizieR On-line Data Catalog: I / 239. (originally published in: bibcode : 1997HIP ... C ...... 0E ). 1997. bibcode : 1997yCat.1239 .... 0E . Corresponding database entry for Alkor on VizieR .
  11. ^ Research vessels «Facilities« Center «GEOMAR - Helmholtz Center for Ocean Research Kiel. Retrieved March 10, 2017 .