78 Ursae Majoris
78 Ursae Majoris is a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.93. Parallax estimates by Hipparcos put it at a distance of 83 light-years (25 pc), but it is drifting closer with a radial velocity of −5 km/s. The system is a candidate member of the Ursa Major Moving Group.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 13h 00m 43.69949s |
| Declination | +56° 21′ 58.8102″ |
| Apparent magnitude (V) | 4.93 (5.02 + 7.88) |
| Characteristics | |
| Evolutionary stage | main sequence |
| Spectral type | F2V + G6V |
| U−B color index | +0.00 |
| B−V color index | +0.368±0.010 |
| Astrometry | |
| Radial velocity (Rv) | −5.1±0.9 km/s |
| Proper motion (μ) | RA: 107.94 mas/yr Dec.: 2.05 mas/yr |
| Parallax (π) | 39.30 ± 0.38 mas |
| Distance | 83.0 ± 0.8 ly (25.4 ± 0.2 pc) |
| Absolute magnitude (MV) | +2.84 |
| Orbit | |
| Period (P) | 104.9±0.6 yr |
| Semi-major axis (a) | 1.208±0.010″ |
| Eccentricity (e) | 0.388±0.009 |
| Inclination (i) | 46.9±0.9° |
| Longitude of the node (Ω) | 88.0±1.1° |
| Periastron epoch (T) | B 1921.224±0.403 |
| Argument of periastron (ω) (secondary) | 119.2±1.5° |
| Details | |
| 78 UMa A | |
| Mass | 1.34 M☉ |
| Radius | 1.62±0.24 R☉ |
| Luminosity | 5.75 L☉ |
| Surface gravity (log g) | 4.26±0.14 cgs |
| Temperature | 6,908±235 K |
| Metallicity [Fe/H] | 0.01±0.05 dex |
| Rotation | 19.2 ± 2.9 h |
| Rotational velocity (v sin i) | 91.7±4.6 km/s |
| Age | 785 Myr |
| Other designations | |
| Database references | |
| SIMBAD | The system |
| A | |
| B | |
The binary nature of this system was announced by S. W. Burnham in 1894. The pair orbit each other with a period of 105 years and an eccentricity of 0.39. Their semimajor axis has an angular size of 1.2″ and the orbital plane is inclined by 47°.
The primary member, designated component A, has a magnitude of 5.02 and is an F-type main-sequence star with a stellar classification of F2V. It is 785 million years old and is spinning with a projected rotational velocity of 92 km/s. The star has 1.34 times the mass of the Sun and is radiating 5.75 times the Sun's luminosity from its photosphere at an effective temperature of 6,908 K.
The secondary, designated component B, has a visual magnitude of 7.88. It is a G-type main-sequence star with a class of G6V. The star is a suspected variable.