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.[2] Based upon an annual parallax shift of 13.24 mas,[1] 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.[6]
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 10h 53m 58.74035s[1] |
| Declination | +43° 11′ 23.8483″[1] |
| Apparent magnitude (V) | 4.61[2] |
| Characteristics | |
| Spectral type | A1VsSi:[3] or A0 IV−V[4] |
| U−B color index | −0.11[2] |
| B−V color index | −0.04[2] |
| Astrometry | |
| Radial velocity (Rv) | −18.70±0.80[5] km/s |
| Proper motion (μ) | RA: +42.97[1] mas/yr Dec.: −23.62[1] mas/yr |
| Parallax (π) | 13.24 ± 0.50 mas[1] |
| Distance | 246 ± 9 ly (76 ± 3 pc) |
| Absolute magnitude (MV) | +0.86[6] |
| Orbit[7] | |
| 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[8] R☉ |
| Luminosity | 76[9] L☉ |
| Surface gravity (log g) | 3.88[4] cgs |
| Temperature | 9,647[9] K |
| Rotational velocity (v sin i) | 47[10] km/s |
| Age | 325[6] 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.[7] The primary member, component A, is an A-type main sequence star with a stellar classification of A1VsSi:.[3] 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.[12] In particular, it has an abnormal abundance of silicon.[13]
Naming
In Chinese, 天牢 (Tiān Láo), meaning Celestial Prison, refers to an asterism consisting of ω Ursae Majoris, 57 Ursae Majoris, 47 Ursae Majoris, 58 Ursae Majoris, 49 Ursae Majoris and 56 Ursae Majoris. Consequently, the Chinese name for ω Ursae Majoris itself is 天牢一 (Tiān Láo yī, English: the First Star of Celestial Prison.).[14]