Mizar

The title of this article is ambiguous. Further meanings are listed under Mizar (disambiguation) .

Database links to Mizar

Double star Mizar (ζ Ursae Majoris)
Mizar A and B
Observation dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation	Big Bear
Apparent brightness	2.06 mag
Astrometry
Radial velocity	−7.6 ± 1.0 km / s
parallax	39.36 ± 0.30 mas
distance	82.9 ± 0.7 ly (25.4 ± 0.2 pc )
Absolute visual brightness M vis	0.04 mag
Proper movement :
Rec. Share:	121.2 ± 0.5 mas / a
Dec. portion:	−22.0 ± 0.5 mas / a
orbit
period	some millennia
Individual data
Names	A; B.
Observation data:
Right ascension	A.	13 h 23 m 55.54 s
	B.	13 h 23 m 56.33 s
declination	A.	+ 54 ° 55 ′ 31.3 ″
	B.	+ 54 ° 55 ′ 18.6 ″
Apparent brightness	A.	2.27 mag
	B.	3.95 likes
Typing:
Spectral class	A.	A1 VpSrSi
	B.	Am (kA1hA2mA7)
B − V color index	A.	0.02
	B.	0.13
U − B color index	A.	0.03
	B.	0.09
Physical Properties:
Absolute vis. Brightness M vis	A.	0.25 mag
	B.	1.93 likes
Absolute bol. Brightness M bol	A.	≈ 0.16 mag
	B.
Dimensions	A.	4.4605 ± 0.044 M ☉
	B.	≈ 3.9 M ☉
radius	A.	2.4 ± 0.1 / 2.4 ± 0.1 R ☉
	B.
Luminosity	A.	33.3 ± 2.1 / 33.3 ± 2.1 L ☉
	B.
Effective temperature	A.	9,000 ± 200 / 9,000 ± 200 K.
	B.
Age	500 ± 100 million a
Other names and catalog entries
Bayer name ζ Ursae Majoris Flamsteed name 79 Ursae Majoris Bonn survey BD + 55 ° 1598 Hipparcos catalog HIP 65378 [1] Bright Star Catalog HR 5054 HR 5055 Henry Draper Catalog HD 116656 HD 116657 SAO catalog SAO 28737 SAO 28738 Tycho catalog TYC 3850-1385-1 [2] TYC 3850-1386-1 [3] WDS catalog WDS 13239 + 5456 Further designations: Σ1744; CCDM 13240 + 5456   FK5 497; FY 3783 FY 3784

Mizar ( Arabic مئزر, DMG miʾzar  'belt / loincloth') or ζ Ursae Majoris ( Zeta Ursae Majoris , ζ UMa for short ) is a star in the constellation Big Bear and the middle tiller star of the Big Dipper. Mizar has an apparent magnitude of 2.06 mag. It is not a single star, but a multiple star system that is about 83 light-years from the Sun and is a member of the Ursa Major Group . Together with Alkor , Mizar forms a double star that is visible to the naked eye .

observation

Mizar is the second star in the tail of the Ursa Major constellation (top left).

Particularly well known is Mizar, because he already a freiäugig has visible companion Alcor , the 4.0 likes is bright and can be seen well under dark skies with normal vision ( see also: Eye Examiner ). Mizar itself is a visual double star that can be separated with telescopes and telescopes from a lens aperture of about 5 cm. The components are 2.27 mag and 3.95 mag light (together 2.06 mag) and are 14.4 arc seconds apart.

History of exploration

As a double star that can be separated with the naked eye, Mizar was known in connection with Alkor long before the invention of the telescope. Medieval Arabic sources ( Qazwini , Fairuzabadi) report that the double star is said to have served as an eye test. The folkloric interpretation as horse and rider is particularly well-known , with Mizar representing the horse and Alkor the rider or the rider . The original name of the star, Mirak (also the name for β Ursae Majoris ), was wrongly changed in the 16th century by JJ Scaliger to the name Mizar (Arabic miʾzar "belt", "loincloth"), which is still in use today .

Mizar was the first double star to be recognized as such with the help of a telescope . It is often mentioned in the literature that Giovanni Riccioli was the first to discover the double star nature of Mizar around 1650. The basis for this is a short note in his Almagestum novum from 1651: "... there seems to be only one star in the middle of the Great Bear's drawbar, although there are actually two, as the telescope reveals." In fact, Benedetto Castelli comes as the most likely explorer in question as he asked Galileo Galilei in a letter dated January 7, 1617 to observe this star (suggesting that Castelli was aware of the binary star nature). Shortly afterwards (probably on January 15, 1617) Galileo himself saw Mizar separated in the telescope. Galileo also tried (unsuccessfully) to measure a fixed star parallax , with the proof of which he would have received an important argument for the heliocentric worldview . Since the existence of physical double stars was not yet known at that time and he assumed that the brighter component must be closer to the earth than the weaker one, this star appeared to him as a suitable test object. The successful measurement of a fixed star parallax was only to be achieved by Friedrich Wilhelm Bessel in 1838 on the star 61 Cygni .

On December 2, 1722 Johann Georg Liebknecht observed a star of the eighth magnitude (later cataloged as HD 116798) lying between Mizar and Alkor and mistakenly believed it to be a new planet, which he named Sidus Ludoviciana ("Ludwig's star", named in honor of Ludwig V . of Hessen-Darmstadt ). HD 116798 is just a background star.

Mizar was the first double star of which an astrophotography was made and in which distance and position angle determinations were made by astrophotography (April 27, 1857 at the Harvard College Observatory ).

Antonia C. Maury was the first to notice that the spectral lines of the brighter component of Mizar (Mizar A) periodically split or shift; this marked the discovery of the spectroscopic binary stars (announced on November 13, 1889 by Edward C. Pickering at the meeting of the National Academy of Sciences ). The fact that the weaker component Mizar B is also a spectroscopic binary star was independently determined by the astronomers Hans Ludendorff and Edwin B. Frost and published in 1908. The orbital period of Mizar B could only be determined in the 1960s at the Dominion Astrophysical Observatory (Canada).

From the 1920s onwards, certain spectroscopic binary stars (including Mizar A) could be resolved by means of interferometry , which is not possible with "ordinary" telescopes due to the atmospheric turbulence . As early as 1925 and 1927, the distances and position angles in the Mizar-A system were measured with the aid of the 20-foot Michelson interferometer at the Mount Wilson observatory . In May / June 1996 the first pictures of the then new Navy Prototype Optical Interferometer (NPOI), a new generation of optical interferometers, were taken by Mizar A. The NPOI located near Flagstaff (Arizona, United States of America) achieved a resolution of 3 milli-angle seconds.

According to a study by George A. Gontcharov and Olga V. Kiyaeva from 2010, Mizar A could have another, as yet undiscovered companion. The final proof is still pending.

Mizar as a star system

Mizar is a four-star system. It is made up of two spectroscopic binary stars ( Mizar A and Mizar B ), which form a superordinate system.

Mizar A ( ζ ¹ Ursae Majoris , V  = 2.27 mag, consisting of Mizar Aa and Mizar Ab ) is one of the Ap stars and has the spectral class A1 VpSrSi ("p" indicates chemical peculiarity and "SrSi" indicates unusual strong lines of strontium and silicon in the spectrum). Interferometric measurements at the NPOI and their combination with older radial velocity data (Hummel et al. 1998) result in a system mass of 4.93 ± 0.14  M _⊙ and an orbit inclination of 60.5 °. New precise radial velocity measurements (Behr et al. 2011) following the use of these orbital inclination 4.46 ± 0.05 M _⊙ wherein on Mizar Aa 2.22 M _⊙ and Mizar from 2.24 M _⊙ omitted. The main sequence stars , which are almost identical in their properties , both belong to the spectral class A2 (± 1 subclass) and each have an effective temperature of approx. 9,000  K , a radius of 2.4  R _⊙ and a luminosity of approx. 33  L _⊙ . They orbit each other with an orbital period of 20.54 days, with their mutual distance varying between 16 and 54 million km (0.1-0.4  AU ). The maximum apparent distance is 0.01 ″ at most. Mizar A is a double-lined spectroscopic binary (SB2 for short), which means the periodic splitting of the spectral lines in the line spectrum and thus the visibility of the lines of both components ( see: Radial velocity , Doppler effect ).

Mizar B ( ζ ² Ursae Majoris , V  = 3.95 mag, consisting of Mizar Ba and Mizar Bb ) was classified as a metal line star (Am star); the spectral class kA1hA2mA7 means that the star based on the K line of calcium ("k") has the spectral type A1, based on the hydrogen lines ("h") the spectral type A2 and based on the metal lines ("m") the spectral type A7 owns. The orbital period of the single stars is 175.6 days. They form a single-lined spectroscopic binary (SB1 for short) in which only the lines of the main star are visible and periodically shift. The lines of the companion do not show up, which suggests a greater difference in brightness between the components (overexposure to the companion) and consequently relatively different physical properties. Mizar Ba has around 1.8 M _⊙ , while the mass of Mizar Bb, the exact nature of which is unknown, is limited between 0.24 M _⊙ and ≈ 0.66 M _⊙ . However, Gutmann (1965) estimated the mass of the Mizar B system to be around 80 percent of Mizar A, which (based on the Mizar A mass according to Hummel et al. 1998) would be around 3.9 M _⊙ .

The path elements of the individual systems are:

Track element	for Mizar A		for Mizar B
	according to Hummel et al. (1998)	after Pourbaix (2000)	after Gutmann (1965)
Orbital time	20.538 35 ± 0.000 05 d	20.538 66 ± 0.000 14 d	175.57 ± 0.07 d
Epoch of the periastron	JD 2,447,636.07 ± 0.02	B 1963.151 00 ± 0.000 08	JD 2,437,295.9 ± 1.2
eccentricity	0.535 4 ± 0.002 5	0.529 ± 0.005 2	0.463 ± 0.019
Major semi-axis	0.009 83 ± 0.000 03 ″	0.010 0 ± 0.000 32 ″	indefinite
Orbit inclination	60.5 ± 0.3 °	61 ± 1.2 °	indefinite
Argument of the node	106.0 ± 0.4 °	106 ± 1.1 °	indefinite
Argument of the periapsis	104.3 ± 0.3 °	105.5 ± 0.79 °	6.9 ± 3.7 °

The two star systems now in turn orbit each other in a higher-level system. The distances and position angles from Mizar B to A were 13.9 "and 143 ° in 1755 and 14.4" and 153 ° in 2017. So Mizar B has moved 10 ° around Mizar A within 262 years and increased the distance by 0.5 ″. This observed arc is too small to be able to determine the complete path from it. The period of revolution is estimated to be several millennia.

The evaluation of astrometric data from Hipparcos and other star catalogs resulted in Mizar A suspecting irregular proper movement, which would indicate another component in the system. Gontcharov and Kiyaeva (2010) give a mass of 1.5 ± 0.4 M _⊙ and an orbital period of ≈ 37 years around Mizar A for this uncertain component and suggest a binary star made up of two dwarf stars as the most suitable explanation . However, since the data scatter too much to be able to clearly prove the irregular proper movement, the existence of this new component remains questionable.

Question of the togetherness of Mizar and Alkor

To date it has not been clarified whether Alkor is gravitationally bound to Mizar and goes into an orbit around him (physical double star), or whether it is just two relatively close neighboring star systems without mutual influence (optical double star) or at least without a closed orbit. In the former case, Mizar and Alkor would form a six-fold star system, since Alkor is also a binary star system.

Mizar and Alkor are core members of the Ursa Major Movement Cluster , the core area of ​​which consists of 15 stars or star systems, has about 28 M _⊙ and covers a space of about 100 cubic parsecs. Thus Mizar and Alkor show a similar proper motion and radial velocity from the start or share these values ​​with those of the cluster. The space velocity of Mizar and Alkor differs only slightly with 2.7 ± 0.8 km / s. The apparent distance is 11.8 arc minutes; given the apparent size of the cluster core area (around 200 square degrees ) these are unusually close together. The most accurate distance determinations to date for Mizar are the dynamic parallax of 39.4 ± 0.3 mas (Hummel et al. 1998) and the trigonometric parallax of 38.01 ± 1.71 mas obtained from the Hipparcos mission (revised Hipparcos catalog , van Leeuwen 2007) - this gives a weighted mean of 39.36 ± 0.30 mas (≙ 82.9 ± 0.7 ly). The trigonometric parallax for Alkor is 39.91 ± 0.13 mas (≙ 81.7 ± 0.3 ly). From this, the distance between Mizar and Alkor was calculated as 74,000 ± 39,000  AU (1.2 ± 0.7 ly) via Monte Carlo simulation . The smallest possible mathematical distance is 17 800 AU (0.3 ly). For comparison: the most massive star of the cluster, the core member Alioth (ε Ursae Majoris), is 6.6 ± 0.1 ly away from Alkor. Given these aspects, the possibility that Mizar and Alkor form a superordinate star system cannot be ruled out.

Computer simulations show that in dense star clusters with a formation density of over 100 M _⊙ per cubic parsec, the formation of physical binary stars with a mutual distance of over 10,000 AU is prevented because the surrounding stars would disrupt the orbit. Accordingly, Alkor could never complete a full circle around Mizar. If Mizar and Alkor form a physical multiple star system, they would represent a counterexample, which suggests an initial upper density limit of the Ursa major cluster of 100 M _⊙ per cubic parsec. It would then be the second closest known six-fold star system after Castor (distance ≈ 52 ly).

See also

• List of the brightest stars

Web links

Commons : Mizar  - collection of images, videos and audio files

• Database entries on SIMBAD : Mizar (treated as a single rating) , Mizar A , Mizar B .
• Leos Ondra: A New View of Mizar (English). In: Sky & Telescope . Vol. 108, No. 1, 2004, p. 72 ff. Extensive article on the history of Mizar's research.
• Leos Ondra: Riccioli On Mizar (English).
• http://stars.astro.illinois.edu/sow/mizar.html

Individual evidence

1. ↑ ^{a b} Jorge R. Ducati: VizieR Online Data Catalog: Catalog of Stellar Photometry in Johnson's 11-color system . In: CDS / ADC Collection of Electronic Catalogs, 2237 . 2002. bibcode : 2002yCat.2237 .... 0D . VizieR catalog entry .
2. ↑ ^{a b c d e f} Eric E. Mamajek et al. : Discovery of a Faint Companion to Alcor Using MMT / AO 5 µm Imaging . In: The Astronomical Journal . Vol. 139, Issue 3, 2010, pp. 922-924. bibcode : 2010AJ .... 139..919M , doi: 10.1088 / 0004-6256 / 139/3/919 , arxiv : 0911.5028 .
3. ↑ Derived from parallax ( π = 39.36 ± 0.30 mas, Mamajek et al. 2010).
4. ↑ ^{a b c d e f g h i j} Leos Ondra: A New View of Mizar . In: Sky & Telescope . Vol. 108, No. 1, 2004, p. 72 ff. Bibcode : 2004S & T ... 108A..72O .
5. ↑ ^{a b c d e} Dorrit Hoffleit, Wayne H. Warren Jr .: VizieR Online Data Catalog: Bright Star Catalog, 5th Revised Ed. (Hoffleit +, 1991) . In: VizieR On-line Data Catalog: V / 50. Originally published in: 1964BS .... C ...... 0H . 1995. bibcode : 1995yCat.5050 .... 0H . VizieR catalog entry (Mizar A) , VizieR catalog entry (Mizar B) .
6. ↑ Claus Fabricius et al. : VizieR Online Data Catalog: Tycho Double Star Catalog (TDSC) (Fabricius + 2002) . In: VizieR On-line Data Catalog: I / 276. Originally published in: 2002A & A ... 384..180F . 2001. bibcode : 2001yCat.1276 .... 0F . VizieR catalog entry .
7. ↑ ^{a b c} Helmut A. Abt: Visual multiples. VII. MK classifications . In: Astrophysical Journal Supplement Series . Vol. 45, 1981, p. 445. bibcode : 1981ApJS ... 45..437A , doi: 10.1086 / 190719 . VizieR catalog entry .
8. ↑ ^{a b} Calculated from the apparent brightness m _V and parallax π (in arc seconds) according to m _V  −5 ∙ lg (1 / π) + 5 .
9. ↑ Calculated from absolute brightness M _V and bolometric correction BC according to M _V  + BC . The bolometric correction for Mizar is A -0.09 ± 0.06 (Hummel et al. 1998).
10. ↑ ^{a b} Bradford B. Behr et al. : Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. II. Orbits of Double-lined Spectroscopic Binaries . In: The Astronomical Journal . Vol. 142, Issue 1, 2011, Art.-ID 6. bibcode : 2011AJ .... 142 .... 6B , doi: 10.1088 / 0004-6256 / 142/1/6 .
11. ↑ ^{a b c d e f} Christian A. Hummel et al. : Navy Prototype Optical Interferometer Observations of the Double Stars Mizar A and Matar . In: The Astronomical Journal . Vol. 116, Ausg. 5, 1998, pp. 2541, 2547. bibcode : 1998AJ .... 116.2536H , doi: 10.1086 / 300602 .
12. ↑ Jeremy R. King et al. : Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group . In: The Astronomical Journal , Vol. 125, Ausg. 4, 2003, p. 1980. bibcode : 2003AJ .... 125.1980K , doi: 10.1086 / 368241 .
13. ↑ ^{a b} Brian D. Mason et al. : VizieR Online Data Catalog: The Washington Visual Double Star Catalog (Mason + 2001-2014) . Vers. 2019-09-02. In: VizieR On-line Data Catalog: B / wds. Originally published in: 2001AJ .... 122.3466M . 2019. bibcode : 2019yCat .... 102026M . VizieR catalog entry .
14. ↑ Richard Hinckley Allen: Star-Names and Their Meanings . GE Stechert, New York / London / Leipzig / Paris 1899, pp. 440–441, 445–446.
15. ↑ ^{a b c} F. Gutmann: The spectroscopic orbit of ζ ¹ Ursae Majoris (Mizar B) . In: Publications of the Dominion Astrophysical Observatory Victoria . Vol. 12, Ed. 11, 1965, pp. 361, 369. bibcode : 1965PDAO ... 12..361G .
16. ↑ James A. Benson et al. : Multichannel optical aperture synthesis imaging of ζ ¹ Ursae Majoris with the Navy prototype optical interferometer . In: The Astronomical Journal . Vol. 114, 1997, pp. 1221-1226. bibcode : 1997AJ .... 114.1221B , doi: 10.1086 / 118554 .
17. ↑ ^{a b} George A. Gontcharov, Olga V. Kiyaeva: Photo Centric orbits from a direct combination of ground-based astrometry with Hipparcos II Preliminary orbits for six astrometric binaries. . In: New Astronomy . Vol. 15, Issue 3, 2010. pp. 324-331. bibcode : 2010NewA ... 15..324G , doi: 10.1016 / j.newast.2009.09.006 , arxiv : 1606.08182 .
18. ^ Klaus Fuhrmann: Nearby stars of the Galactic disc and halo - IV . In: Monthly Notices of the Royal Astronomical Society . Vol. 184, Ed. 1, 2008, pp. 209-210. bibcode : 2008MNRAS.384..173F , doi: 10.1111 / j.1365-2966.2007.12671.x .
19. ↑ Dimitri Pourbaix: Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses . In: Astronomy and Astrophysics Supplement Series . Vol. 145, 2000, p. 218. bibcode : 2000A & AS..145..215P , doi: 10.1051 / aas: 2000237 .