Tau Ursae Majoris
Tau Ursae Majoris (τ UMa) is the Bayer designation for a binary star in the northern circumpolar constellation of Ursa Major. It is visible to the naked eye, having an apparent visual magnitude of 4.66. With an annual parallax shift of 25.82 mas, it is located about 126 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.19 due to interstellar dust.
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h 10m 55.06553s |
| Declination | +63° 30′ 49.0553″ |
| Apparent magnitude (V) | 4.66 |
| Characteristics | |
| Spectral type | kA5hF0mF5 II |
| U−B color index | +0.14 |
| B−V color index | +0.35 |
| Astrometry | |
| Radial velocity (Rv) | −9.80±0.30 km/s |
| Proper motion (μ) | RA: +102.37 mas/yr Dec.: −63.55 mas/yr |
| Parallax (π) | 25.82 ± 0.54 mas |
| Distance | 126 ± 3 ly (38.7 ± 0.8 pc) |
| Absolute magnitude (MV) | +1.73 |
| Orbit | |
| Period (P) | 1,062.4 d |
| Eccentricity (e) | 0.48 |
| Periastron epoch (T) | 2425721.6 JD |
| Argument of periastron (ω) (secondary) | 349.4° |
| Semi-amplitude (K1) (primary) | 3.9 km/s |
| Details | |
| τ UMa A | |
| Mass | 1.8±0.1 M☉ |
| Luminosity | 16 L☉ |
| Surface gravity (log g) | 3.86±0.43 cgs |
| Temperature | 7,343±100 K |
| Metallicity [Fe/H] | +0.57±0.15 dex |
| Rotational velocity (v sin i) | 21 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is a single-lined spectroscopic binary star system with an orbital period of 2.9 years and an eccentricity of 0.48. The primary member, component A, is an evolved bright giant with a stellar classification of kA5hF0mF5 II. This notation indicates the star's spectrum shows the calcium K lines of an A5 star, the hydrogen lines of an F0 star, and the metallic lines of an F5 star. It is an evolved Am star of the ρ Puppis type, a class of evolved stars showing the Am chemical peculiarities. It is located in the instability strip of the Hertzsprung–Russell diagram but is not thought to be variable.