Phi Ursae Majoris
Phi Ursae Majoris, Latinized from φ Ursae Majoris, is binary star system in the northern constellation of Ursa Major. It is white-hued and is visible to the naked eye with a combined apparent visual magnitude of +4.60; the primary is magnitude 5.28 while the secondary is magnitude 5.39. The system is located at a distance of approximately 510 light-years (160 parsecs) from the Sun based on parallax, but is drifting closer with a radial velocity of −14.7 km/s. It should make its closest approach at a distance of around 370 light-years in about 4.7 million years.
Location of φ Ursae Majoris (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 52m 06.35437s |
| Declination | +54° 03′ 51.5962″ |
| Apparent magnitude (V) | +4.60 (5.28 + 5.39) |
| Characteristics | |
| Spectral type | A3 IV + A3 IV |
| U−B color index | +0.08 |
| B−V color index | +0.03 |
| Astrometry | |
| Radial velocity (Rv) | −14.7±0.3 km/s |
| Proper motion (μ) | RA: −6.00 mas/yr Dec.: +19.16 mas/yr |
| Parallax (π) | 6.41 ± 0.59 mas |
| Distance | 510 ± 50 ly (160 ± 10 pc) |
| Absolute magnitude (MV) | −1.39 |
| Orbit | |
| Period (P) | 104.6 yr |
| Semi-major axis (a) | 0.329″ |
| Eccentricity (e) | 0.436 |
| Inclination (i) | 19.4° |
| Longitude of the node (Ω) | 132.5° |
| Periastron epoch (T) | 1987.52 |
| Argument of periastron (ω) (secondary) | 33.3° |
| Details | |
| A | |
| Mass | 3.5±0.2 M☉ |
| Luminosity | 347 L☉ |
| Surface gravity (log g) | 3.69±0.16 cgs |
| Temperature | 8,769±150 K |
| Metallicity [Fe/H] | −0.23±0.08 dex |
| Rotational velocity (v sin i) | 28 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
As of 2017, the components had an angular separation of 0.50″ along a position angle of 304°. They are orbiting each other with a period of 105.4 years and eccentricity of 0.44. Both of components are A-type subgiant stars with a stellar classification of A3 IV.
Phi Ursae Majoris is moving through the galaxy at a speed of 21.6 km/s relative to the Sun. Its projected galactic orbit carries it between 24,000 and 46,000 light-years from the center of the galaxy.