Omega Ursae Majoris
Omega Ursae Majoris (Omega UMa, ω Ursae Majoris, ω UMa) is the Bayer designation for a binary star system in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye with an apparent visual magnitude of 4.61. Based upon an annual parallax shift of 13.24 mas, it is roughly 246 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction factor of 0.11 due to interstellar dust.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 10h 53m 58.74035s |
| Declination | +43° 11′ 23.8483″ |
| Apparent magnitude (V) | 4.61 |
| Characteristics | |
| Spectral type | A1VsSi: or A0 IV−V |
| U−B color index | −0.11 |
| B−V color index | −0.04 |
| Astrometry | |
| Radial velocity (Rv) | −18.70±0.80 km/s |
| Proper motion (μ) | RA: +42.97 mas/yr Dec.: −23.62 mas/yr |
| Parallax (π) | 13.24 ± 0.50 mas |
| Distance | 246 ± 9 ly (76 ± 3 pc) |
| Absolute magnitude (MV) | +0.86 |
| Orbit | |
| Period (P) | 15.8307 d |
| Eccentricity (e) | 0.31 |
| Periastron epoch (T) | 2435185.246 JD |
| Argument of periastron (ω) (secondary) | 27.3° |
| Semi-amplitude (K1) (primary) | 22.2 km/s |
| Details | |
| Radius | 2.5 R☉ |
| Luminosity | 76 L☉ |
| Surface gravity (log g) | 3.88 cgs |
| Temperature | 9,647 K |
| Rotational velocity (v sin i) | 47 km/s |
| Age | 325 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is a single-lined spectroscopic binary star system with an orbital period of 15.8 days and an eccentricity of 0.31. The primary member, component A, is an A-type main sequence star with a stellar classification of A1VsSi:. The stellar spectrum has the appearance of a hot Am star, showing overabundances of many iron-peak and heavier elements, but an underabundance of helium. In particular, it has an abnormal abundance of silicon.