Megrez

Database links to δ Ursae Maioris

Star Megrez (δ Ursae Maioris)
δ UMa in the constellation "Great Bear"
AladinLite
Observation dates equinox :  J2000.0 , epoch : J2000.0
Constellation	Big Bear
Right ascension	12 h 15 m 25.56 s
declination	+ 57 ° 1 ′ 57.4 ″
Apparent brightness	3.34 mag
Typing
B − V color index	0.09
U − B color index	0.05
R − I index	0.00
Spectral class	A2 Vn
Variable star type	irregular.
Astrometry
Radial velocity	(−15.3 ± 0.5) km / s
parallax	(40.51 ± 0.15)  mas
distance	(80.5 ± 0.3)  ly (24.7 ± 0.1)  pc
Proper movement
Rec. Share:	(104.11 ± 0.14)  mas / a
Dec. portion:	(7.30 ± 0.13)  mas / a
Physical Properties
Dimensions	(2)  M ☉
radius	(2)  R ☉
Luminosity	(23)  L ☉
Age	(50) mill.  A
Other names and catalog entries
Bayer name δ Ursae Maioris Flamsteed name 69 Ursae Maioris Bonn survey BD + 57 ° 1363 Bright Star Catalog HR 4660 [1] Henry Draper Catalog HD 106591 [2] Gliese catalog FY 459 [3] Hipparcos catalog HIP 59774 [4] SAO catalog SAO 28315 [5] Tycho catalog TYC 3837-1070-1 [6] 2MASS catalog 2MASS J12152554 + 5701575 [7] Other names Megrez, FK5 456 WDS 12154 + 5702 CCDM 12155 + 5702

Megrez (from Arabic مغرز, DMG maġriz  'attachment point [of the tail]') is the proper name of the star Delta Ursae Maioris (δ UMa) in the constellation Great Bear . It stands in the big wagon on the corner where the drawbar connects and is much fainter than the six other stars in the "wagon". Megrez has an apparent magnitude of 3.3 mag and is about 80 light years away.

Megrez is a white main sequence star with about twice the mass, twice the diameter and about 20 times the luminosity of the sun . Its surface temperature is around 8630 K. The star shows slight fluctuations in brightness with an amplitude of 0.07 mag, but it has not yet been able to be assigned to any type of variable.

Megrez is a multiple star optical system. As early as 1878 and 1879, two weaker components B and C were found in addition to the 3.3 mag bright main star A. They only have a brightness of 10.2 or 11.6 mag and are each about 3 arc minutes away from the main star. According to parallax data from Gaia DR2 , these two stars (TYC 3837-884-1 and TYC 3837-771-1) are, however, about 1000 light years apart, both significantly further away than Megrez and therefore do not form a physical multiple star system with it. In 2010 two more components D and E were found. These are very faint stars with 18–19 mag brightness, which are very close to the main star with a distance of 3–6 arc seconds .

With four other of the seven bright chariot stars, Megrez belongs to the so-called bear group , a moving cluster of over a hundred stars spread across half the sky. Our sun is in the range of this group, but moves in a different direction.

An alternative name for the star is "Kaffa". According to the “IAU Catalog of Star Names” of the Working Group on Star Names (WGSN) of the IAU for the standardization of star names, however, the name “Megrez” was officially assigned to the star δ Ursae Maioris in 2016.

Individual evidence

1. ^ ^{A b c d} VizieR: Hipparcos, the New Reduction (van Leeuwen, 2007) - The Astrometric Catalog
2. ↑ ^{a b c d} del UMa. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed September 16, 2019 . 
3. ↑ VizieR: Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006)
4. ↑ ^{a b c d} Megrez. Jim Kaler, accessed September 16, 2019 . 
5. ↑ VizieR: AAVSO International Variable Star Index VSX (Watson +, 2006-2014)
6. ↑ Gaia DR2 1575286767429930112. In: VizieR . Center de Données astronomiques de Strasbourg, accessed September 17, 2019 . 
7. ↑ Gaia DR2 1575286221969426176. In: VizieR. Center de Données astronomiques de Strasbourg, accessed September 17, 2019 . 
8. ↑ VizieR: The Washington Visual Double Star Catalog (Mason + 2001-2014)
9. ^ A. Bečvář: Atlas of the Heavens - II Catalog 1950.0. Cambridge MA, 1964, p. 349 ( PDF; 14.8 MB ).
10. ↑ Bulletin of the IAU Working Group on Star Names, No. 2. IAU Division C Education, Outreach and Heritage, 2016 ( PDF; 158 kB ).