Delta Ursae Majoris

From Infogalactic: the planetary knowledge core
Jump to: navigation, search
Delta Ursae Majoris
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings

Location of δ Ursae Majoris (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 12h 15m 25.56063s[1]
Declination +57° 01′ 57.4156″[1]
Apparent magnitude (V) +3.312[2]
Characteristics
Spectral type A3 V[3]
U−B color index +0.067[2]
B−V color index +0.075[2]
Astrometry
Radial velocity (Rv) -20.2[4] km/s
Proper motion (μ) RA: +143.42[1] mas/yr
Dec.: -129.88[1] mas/yr
Parallax (π) 55.82 ± 0.25[1] mas
Distance 58.4 ± 0.3 ly
(17.91 ± 0.08 pc)
Details
Mass 1.63[5] M☉
Radius 1.4[6] R☉
Luminosity 14[6] L☉
Surface gravity (log g) 4.49[6] cgs
Temperature 9,480 ± 570[6] K
Rotational velocity (v sin i) 233[7] km/s
Age 0.3[8] Gyr
Other designations
Megrez, δ Ursae Majoris, δ UMa, Delta UMa, 69 Ursae Majoris, BD+57 1363, CCDM J12155+5702A, FK5 456, GC 16736, HD 106591, HIP 59774, HR 4660, IDS 12105+5735 A, PPM 33469, SAO 28315, WDS J12154+5702A.[9]
Database references
SIMBAD data
Book plate by Sydney Hall depicting Ursa Major's stars

Delta Ursae Majoris (Delta UMa, δ Ursae Majoris, δ UMa) is the Bayer designation for a star in the northern circumpolar constellation of Ursa Major. It has the traditional names Megrez /ˈmɛɡrɛz/, and Kaffa. Megrez has an apparent magnitude of +3.3,[2] making it the dimmest of the seven stars in the Big Dipper asterism. Parallax measurements yield a distance estimate of 58.4 light-years (17.9 parsecs) from Earth.[1]

Megrez has 63%[5] more mass of the Sun and is about 1.4[6] times the Sun's radius. It has a stellar classification of A3 V,[3] which means it is an A-type main sequence star that is generating energy at its core through the nuclear fusion of hydrogen. It shines at 14[6] times the luminosity of the Sun, with this energy being emitted from its outer envelope at an effective temperature of 9,480 K.[6] This gives it the white hue typical of an A-type star.[10]

This star has an excess emission of infrared radiation, indicating the presence of circumstellar matter. This forms a debris disk around an orbital radius of 16 Astronomical Units from the star. This radius is unusually small for the estimated age of the disk, which may be explained by drag from the Poynting–Robertson effect causing the dust to spiral inward.[8]

It has two faint companions, a 10th magnitude star and an 11th magnitude star, both at an angular separation of two arcminutes from the primary.[11]

Megrez is a marginally outlying member of the Ursa Major moving group, an association of stars that share a common motion through space and likely formed in the same molecular cloud. The space velocity components of Delta Ursae Majoris in the galactic coordinate system are [U, V, W] = [+15.35, +1.17, –11.52] km s−1.[12]

Name and etymology

The traditional name Megrez comes from the Arabic Arabic: المغرز‎‎ al-maghriz "the base [of the bear's tail]". The Proper Name Kaffa for the star appeared in a 1951 publication, Atlas Coeli (Skalnate Pleso Atlas of the Heavens) by Czech astronomer Antonín Bečvář. Professor Paul Kunitzch has been unable to find any clues as to the origin of the name.[13]

Namesakes

USS Megrez (AK-126) was a United States Navy Crater class cargo ship named after the star.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日
Retrieved from "https://infogalactic.com/w/index.php?title=Delta_Ursae_Majoris&oldid=722703340"