Phi Ursae Majoris
Binary star in the constellation Ursa Major
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Phi Ursae Majoris, Latinized from φ Ursae Majoris, is a binary star[11] 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;[2] the primary is magnitude 5.28 while the secondary is magnitude 5.39.[11] The system is located at a distance of approximately 510 light-years (160 parsecs) from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −14.7 km/s.[5] It should make its closest approach at a distance of around 370 light-years in about 4.7 million years.[6]
  Location of φ Ursae Majoris (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 52m 06.35437s[1] |
| Declination | +54° 03′ 51.5962″[1] |
| Apparent magnitude (V) | +4.60[2] (5.28 + 5.39)[3] |
| Characteristics | |
| Spectral type | A3 IV + A3 IV[4] |
| U−B color index | +0.08[2] |
| B−V color index | +0.03[2] |
| Astrometry | |
| Radial velocity (Rv) | −14.7±0.3[5] km/s |
| Proper motion (μ) | RA: −6.00[1] mas/yr Dec.: +19.16[1] mas/yr |
| Parallax (π) | 6.41±0.59 mas[1] |
| Distance | 510 ± 50 ly (160 ± 10 pc) |
| Absolute magnitude (MV) | −1.39[6] |
| Orbit[7] | |
| 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[8] M☉ |
| Luminosity | 347[8] L☉ |
| Surface gravity (log g) | 3.69±0.16[9] cgs |
| Temperature | 8,769±150[9] K |
| Metallicity [Fe/H] | −0.23±0.08[9] dex |
| Rotational velocity (v sin i) | 28[8] km/s |
| Other designations | |
| φ UMi, 30 Ursae Majoris, BD+54°1331, GC 13559, HD 85235, HIP 48402, HR 3894, SAO 27408, PPM 32355, CCDM J09521+5404AB, WDS J09521+5404AB[10] | |
| Database references | |
| SIMBAD | data |
As of 2017, the components had an angular separation of 0.50″ along a position angle of 304°.[3] They are orbiting each other with a period of 105.4 years and eccentricity of 0.44.[7] Both of components are A-type subgiant stars[12] with a stellar classification of A3 IV.[4]
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.[6]
Naming
With τ, h, υ, θ, e, and f, it composed the Arabic asterism Sarīr Banāt al-Na'sh, the Throne of the daughters of Na'sh, and Al-Haud, the Pond.[13] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al-Haud were the title for seven stars: f as Alhaud I, τ as Alhaud II, e as Alhaud III, h as Alhaud IV, θ as Alhaud V, υ as Alhaud VI and this star (φ) as Alhaud VII.[14]
In Chinese, 文昌 (Wén Chāng), meaning Administrative Center, refers to an asterism consisting of φ Ursae Majoris, υ Ursae Majoris, θ Ursae Majoris, 15 Ursae Majoris and 18 Ursae Majoris. Consequently, the Chinese name for φ Ursae Majoris itself is known as 文昌三 (Wén Chāng sān, English: the Third Star of Administrative Center).[15]