Dubhe

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Triple
Star Dubhe (α Ursae Majoris)
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Observation
data epoch : J2000.0
AladinLite
Constellation Big Bear
Right ascension 11 h 03 m 43.7 s
declination + 61 ° 45 ′ 04 ″
Vis. Brightness
(total) 		1.7 likes
Astrometry
Radial velocity (−8.9 ± 0.9) km / s
distance  124 ly
(37.9 pc )
Individual data
Names A, B, C
Observation data:
Apparent
brightness 		A. +2.02 m
B. +4.73 m
C. +7.12 m
Typing:
Spectral class A. K1II-III
B. K0 V
C. F8 V
Astrometry:
Absolute
visual
brightness M vis 		A. −1.1 mag
B. +1.8 likes
C. +4.2 mag
Physical Properties:
Dimensions A. 4 M ☉
B. 1.7 M ☉
C. M ☉
radius A. 30 R ☉
B. 1.3 R ☉
C. > 1 R ☉
Luminosity A. 224 L ☉
B. 14.9 L ☉
C. ≈ 1.5 L ☉
Designations and catalog entries
Bayer-Bez. α Ursae Majoris
Flamsteed-Bez. 50 Ursae Majoris
Bonn diam. BD + 62 ° 1161
Bright Star Cat. HR 4301
HD catalog HD 95689
SAO catalog SAO 15384
Hipparcos catalog HIP 54061
ADS catalog ADS 8035
Other
names 		FK5 417, 2MASS J11034364 + 6145034, CCDM J11037 + 6145, USNO-B1.0 1517-00189768

Dubhe / ˈDubə / is the name of the star Alpha Ursae Majoris (α UMa) in the constellation Great Bear . It is visible all year round in Central Europe. The name comes from the Arabic wordدب / dubb  / ' bear '.

Despite the Bayer designation “Alpha”, Dubhe is only the second brightest star in the constellation Great Bear and is located in the upper right corner of the Big Dipper box . Together with Merak it forms its end, the extension of which points beyond Dubhe to the Pole Star ( pointer star ).

It is not a member of the Ursa Major Group - the closest physical group of stars with a common velocity - and also belongs to a different spectral group than most of the member stars such as Mizar or Phekda . Dubhe has an apparent magnitude of +1.7 mag, making it one of the 50 brightest stars in the night sky. Its distance is approximately 124 light years .

Structure of the system

The Dubhe system consists of two double stars , with the star Dubhe B orbiting the much more massive Dubhe A at a distance of 22.9 AU (slightly more than the greatest distance between Uranus and the Sun). Dubhe C is in an orbit of more than 8000 AU (0.12 light years) and is composed of a dark class F star and a nearby companion that orbits it in less than 7 days.

In Dubhe A is an orange-yellow giant star at the end of its development. It has 30 times the radius of the sun and 224 times the luminosity. In contrast, it has only four times the solar mass, which results in a low envelope density. The surface temperature is 4800 to 5000 degrees.

In contrast, Dubhe B is still in the hydrogen burning stage. As a class K0 V star, it shines around 15 times as brightly as our sun. It orbits the giant Dubhe A over a period of 44 years.

Dubhe C is approximately 8,000 AU (0.12 light-years) from Dubhe A and consists of an F8 V-class star and a nearby companion orbiting it with a period of just under 7 days. It shines about one and a half times as brightly as our sun and is probably similar in mass and radius as well.

Possibility for planetary systems

Both around Dubhe A and Dubhe B planets could move at a short distance (so-called S-planets). However, a planetary system around Dubhe A would be more likely than around Dubhe B, because the star can hold more satellites due to its greater gravity or Dubhe B literally snatches the planets away.

Any planets around Dubhe C would be outside of an influencing gravitational field of the main star. The companion of Dubhe C does not disturb the planetary orbits due to its small distance. So a larger number of planets could exist around Dubhe C.

See also

Web links

Individual evidence

  1. ↑ a b SIMBAD database