Rho Ursae Majoris (ρ UMa) is the Bayer designation for a solitary[9] star in the northern circumpolar constellation of Ursa Major. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74.[2] The distance to this star, based upon an annual parallax shift of 10.37 mas,[1] is around 315 light years.
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 02m 32.69092s[1] |
| Declination | +67° 37′ 46.6280″[1] |
| Apparent magnitude (V) | 4.74[2] |
| Characteristics | |
| Spectral type | M3 III[3] |
| U−B color index | +1.84[2] |
| B−V color index | +1.56[2] |
| Astrometry | |
| Radial velocity (Rv) | 4.75±0.19[4] km/s |
| Proper motion (μ) | RA: −22.83[1] mas/yr Dec.: +18.13[1] mas/yr |
| Parallax (π) | 10.37 ± 0.25 mas[1] |
| Distance | 315 ± 8 ly (96 ± 2 pc) |
| Absolute magnitude (MV) | +0.06[5] |
| Details | |
| Radius | 58[6] R☉ |
| Luminosity | 464[7] L☉ |
| Temperature | 3,725[7] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
With a stellar classification of M3 III,[3] this is a red giant star on the asymptotic giant branch.[10] It is a suspected small amplitude variable.[11] The measured angular diameter of the star after correcting for limb darkening is 5.64±0.15 mas,[12] which, at the estimated distance of this star, yields a physical size of about 58 times the radius of the Sun.[6] It is radiating 464 times the solar luminosity from its outer atmosphere at an effective temperature of about 3,725 K.[7] Based upon its motion through space, there is a 60.6% chance that this star is a member of the Sirius stream.[5]
Naming
- With π1, π2, σ1, σ2, A and d, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle.[13] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Ṭhibā were the title for seven stars : A as Althiba I, π1 as Althiba II, π2 as Althiba III, this star (ρ) as Althiba IV, σ1 as Althiba V, σ2 as Althiba VI, and d as Althiba VII[14]
- In Chinese, 三師 (Sān Shī), meaning Three Top Instructors, refers to an asterism consisting of ρ Ursae Majoris and σ2 Ursae Majoris. Consequently, the Chinese name for ρ Ursae Majoris itself is 三師一 (Sān Shī yī, English: the First Star of Three Top Instructors.).[15]