Xi Ursae Majoris
Xi Ursae Majoris is a star system in the constellation of Ursa Major. It has the traditional name Alula Australis; Xi Ursae Majoris is the Bayer designation, which is Latinised from ξ Ursae Majoris and abbreviated Xi UMa or ξ UMa. It was the first visual double star for which an orbit was calculated, when it was computed by Félix Savary in 1828. It is also a variable star with a small amplitude. Xi Ursae Majoris is found in the left hind paw of the Great Bear.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Pronunciation | /æˈluːlə ɔːˈstreɪlɪs/ |
| ξ UMa A | |
| Right ascension | 11h 18m 10.902s |
| Declination | +31° 31′ 44.98″ |
| Apparent magnitude (V) | 4.264 |
| ξ UMa B | |
| Right ascension | 11h 18m 10.950s |
| Declination | +31° 31′ 45.74″ |
| Apparent magnitude (V) | 4.729 |
| Characteristics | |
| Spectral type | F8.5:V / G2V |
| U−B color index | 0.04 |
| B−V color index | 0.59 |
| Variable type | RS CVn |
| Astrometry | |
| Radial velocity (Rv) | −18.2±2.7 km/s |
| Proper motion (μ) | RA: −453.7 mas/yr Dec.: −591.4 mas/yr |
| Parallax (π) | 113.2 ± 4.6 mas |
| Distance | 29 ± 1 ly (8.8 ± 0.4 pc) |
| ξ UMa Aa | |
| Absolute magnitude (MV) | 4.66 |
| Absolute bolometric magnitude (Mbol) | 4.54±0.06 |
| ξ UMa Ba | |
| Absolute magnitude (MV) | 5.16 |
| Absolute bolometric magnitude (Mbol) | 5.00±0.06 |
| Orbit | |
| Primary | ξ UMa A |
| Companion | ξ UMa B |
| Period (P) | 59.878 yr |
| Semi-major axis (a) | 2.536″ |
| Eccentricity (e) | 0.398 |
| Inclination (i) | 127.94° |
| Longitude of the node (Ω) | 101.85 (ascending)° |
| Periastron epoch (T) | 1935.195 |
| Orbit | |
| Primary | ξ UMa Aa |
| Companion | ξ UMa Ab |
| Period (P) | 1.832 yr |
| Semi-major axis (a) | 0.057″ |
| Eccentricity (e) | 0.53 |
| Inclination (i) | 94.9° |
| Details | |
| ξ UMa Aa | |
| Mass | 0.97 M☉ |
| Radius | 1.02±0.04 R☉ |
| Luminosity | 1.21 L☉ |
| Surface gravity (log g) | 4.39±0.10 cgs |
| Temperature | 6,005±80 K |
| Rotational velocity (v sin i) | 1.0±1.0 km/s |
| ξ UMa Ab | |
| Mass | 0.38±0.02 M☉ |
| Radius | 0.32 R☉ |
| Temperature | ~3,700 K |
| ξ UMa Ba | |
| Mass | 0.86 M☉ |
| Radius | 0.92±0.04 R☉ |
| Luminosity | 0.79 L☉ |
| Surface gravity (log g) | 4.46±0.10 cgs |
| Temperature | 5,692±90 K |
| Metallicity [Fe/H] | −0.35±0.08 dex |
| Rotational velocity (v sin i) | 3.0±1.0 km/s |
| ξ UMa Bb | |
| Mass | 0.14+0.05 −0.09 M☉ |
| Other designations | |
Alula Australis, ξ Ursae Majoris, ξ UMa, Xi UMa, 53 Ursae Majoris, BD+32°2132, GC 15537, GJ 423, HIP 55203, SAO 62484, CCDM J11182+3132, WDS J11182+3132 | |
| A: HD 98231, HR 4375 | |
| B: HD 98230, HR 4374 | |
| E: WISE J111838.70+312537.9 | |
| Database references | |
| SIMBAD | ξ UMa |
| ξ UMa AB | |
| ξ UMa A | |
| ξ UMa B | |
| ξ UMa Bb | |
| WISE J1118+3125 | |
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