Xi Ursae Majoris
| ξ Ursae Majoris (Alula Australis) |
|
|---|---|
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| Constellation | Big Bear |
| Right ascension | 11 h 18 m 11 s |
| declination | + 31 ° 31 ′ 45 ″ |
| Astrometry | |
| Radial velocity | approx. −16 km / s |
| parallax | (119.5 ± 0.8) mas |
| distance | (27.3 ± 0.2) ly (8.37 ± 0.06) pc |
| Orbits | |
| Period of circulation | AB: 59.8 years Aab: 2 years Bab: 3.98 days |
| Age | about 6 billion years |
| Individual data | |
| Apparent brightness | A: 4.3 likes B: 4.7 likes |
| Spectral class | Aa: G0 V Ab: M3 V Ba: G0 V Bb: L? |
| Metallicity | Aa and Ba: [Fe / H] = −0.35 |
| Designations | |
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ξ Ursae Majoris : 53 Ursae Majoris • HIP 55203 • BD + 32 ° 2132 • Gliese 423 • Σ 1523 • ADS 8119 • WDS J11182 + 3132 ξ Ursae Majoris A : HR 4375 • HD 98231 • TYC 2520-2634-1 |
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ξ Ursae Majoris (Xi Ursae Majoris, short ξ UMa) is a multiple star system with at least four components in the constellation Great Bear at a distance of 27 light years .
Proper names
The star bears the historical proper name Alula Australis . The name Alula comes from arab. (al-Qafza h ) al-Ūlā , "first (jump of the gazelle)") known. Australis means "south". In historical Chinese astronomy, ξ UMa was referred to as Hea Tae (下台) together with ν Ursae Majoris .
The IAU has the historical proper names on 20 July 2016 Alula Australis defined as standardized proper names. However, it should be noted that the proper name is only valid for the visually brightest component A. All other stars or components of this multiple star system therefore have no proper name (yet).
composition
The system consists of two visual components, the lighter one, ξ Ursae Majoris A , having an apparent brightness of 4.3 mag, the darker one, ξ Ursae Majoris B , a brightness of 4.7 mag. Both components are themselves again spectroscopic double systems, which circle each other in almost 60 years. The main components, ξ Ursae Majoris Aa and ξ Ursae Majoris Ba , are two almost identical main sequence stars of the spectral class G0, but have different periods of rotation. The companion of Aa, ξ Ursae Majoris Ab has an orbital period of around 2 years. Ba's companion, ξ Ursae Majoris Bb (also: HD 98230 B ), is a low-mass star or possibly a brown dwarf, which may have been observed by Louis Berman as early as 1931. A minimum mass of 37 Jupiter's masses and a semi-major axis of 0.06 astronomical units were determined. Due to the short orbital period of just under 4 days, it was suggested that the B-system has a bound rotation. The discovery of a possible fifth component (referred to as ξ Ursae Majoris Bc ) using speckle interferometry was made in 1995 by Mason et al. released.
History and scientific significance
The system has a certain role in the history of binary star exploration. The star was recognized as a double star by William Herschel in 1803 . The mutual position of the two components was first measured by Struve in 1837 . With the help of the subsequently obtained measurement data, it was possible for the first time ever to calculate an orbit for a double star.
observation
A telescope with a lens opening of at least 10 centimeters is required to separate the components into individual stars.
Tabular list of the angular distances and the position angles of the main components:
| year | Angular distance | Position angle |
|---|---|---|
| 1992 | 0 ", 9 | 25 ° |
| 1994 | 0 ", 9 | 335 ° |
| 1996 | 1 ", 3 | 304 ° |
| 1998 | 1 ", 6 | 286 ° |
| 2000 | 1 ", 8 | 273 ° |
| 2005 | 1 ", 7 | 243 ° |
| 2010 | 1 ", 6 | 208 ° |
swell
- Ball et al .: Stellar Coronal Abundances at Intermediate Activity Levels: ξ UMa ; in: The Astrophysical Journal , Vol. 634, Issue 2, pp. 1336ff. (2005), bibcode : 2005ApJ ... 634.1336B
Individual evidence
- ↑ Bulletin of the IAU Working Group on Star Names, No. 1, July 2016. (PDF) Retrieved November 9, 2016 (English, 184 KiB).