Xi Ursae Majoris

ξ Ursae Majoris A: HR 4375 HD 98231 • • TYC 2520-2634-1 ξ Ursae Majoris B: HR 4374 HD 98230 • • TYC 2520-2634-2

ξ Ursae Majoris (Xi Ursae Majoris, short ξ UMa ) is a multiple star system with at least four components in the constellation Ursa Major at a distance of 27 light years.

Proper names

The star bears the historic proper name Alula Australis. The name comes from Arabic Alula. (al- Qafzah ) al - Ula, "first (leap of the gazelle ) " ) known. Australis means "south ". In the ancient Chinese astronomy (下台) was ξ UMa along with ν Ursae Majoris as Tae Hea referred.

Composition

The system consists of two visual components, the brighter, ξ Ursae Majoris A, an apparent brightness of 4.3 mag has, the darker, ξ Ursae Majoris B, a brightness of 4.7 mag. Both components are themselves spectroscopic binary systems that orbit each other in almost 60 years. The main components, ξ Ursae Majoris ξ Ursae Majoris Aa and Ba, are two nearly identical main sequence stars of spectral type G0, but have different rotational periods on. The companion of Aa, ξ Ursae Majoris from has an orbital period of approximately 2 years. The companions of Ba, ξ Ursae Majoris Bb (also: HD 98230 B) is a low mass star or possibly a brown dwarf, which was possibly already observed in 1931 by Louis Berman. There a minimum mass of 37 Jupiter masses and a semi-major axis of 0.06 astronomical units was determined. Due to the short orbital period of just under 4 days has been suggested that the B- system has a synchronous rotation. The discovery of a possible fifth component ( ξ Ursae Majoris as referred Bc ) by means of speckle interferometry in 1995 by Mason et al. published.

History and scientific importance

The system comes to a certain role in the history of the study of double stars. The star was recognized in 1803 by William Herschel as a double star. The mutual position of the two components was first measured in 1837 by Struve. With the win in the sequence data for the first time ever an orbit could be calculated for a double star.

Observation

To separate the components into individual stars, a telescope of at least 10 centimeters lens opening is necessary.

Tabulation of the angular distances and the position angle of the major components:

Swell

  • . Ball et al: " Stellar Coronal abundances at Intermediate -Activity Levels: ξ UMa "; In: The Astrophysical Journal, Vol 634, Issue 2, pp. 1336ff. (2005)
  • Binary star
  • Individual fourth star size
  • Yellow Dwarf
  • Big Dipper
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