| |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Ursa Major |
| Right ascension | 09h10m 55.06553s[1] |
| Declination | +63° 30′ 49.0553″[1] |
| Apparent magnitude (V) | 4.66[2] |
| Characteristics | |
| Spectral type | kA5hF0mF5 II[3] |
| U−B color index | +0.14[2] |
| B−V color index | +0.35[2] |
| Astrometry | |
| Radial velocity (Rv) | −9.80±0.30[4] km/s |
| Proper motion (μ) | RA: +102.37[1] mas/yr Dec.: −63.55[1] mas/yr |
| Parallax (π) | 25.82 ± 0.54 mas[1] |
| Distance | 126 ± 3 ly (38.7 ± 0.8 pc) |
| Absolute magnitude (MV) | +1.73[5] |
| Orbit[6] | |
| 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[7] M☉ |
| Luminosity | 16[8] L☉ |
| Surface gravity (log g) | 3.86±0.43[9] cgs |
| Temperature | 7,343±100[9] K |
| Metallicity [Fe/H] | +0.57±0.15[9] dex |
| Rotational velocity (v sin i) | 21[10] km/s |
| Other designations | |
τ UMa, 14 Ursae Majoris, BD+64°723, FK5 2727, HD 78362, HIP 45075, HR 3624, SAO 14796, WDS J09109+6331A[11] | |
| Database references | |
| SIMBAD | data |
Tau Ursae Majoris (τ UMa) is the Bayer designation for a binary star in the northern circumpolar constellationofUrsa Major. It is visible to the naked eye, having an apparent visual magnitude of 4.66.[2] With an annual parallax shift of 25.82 mas,[1] 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.[9]
This is a single-lined spectroscopic binary star system with an orbital period of 2.9 years and an eccentricity of 0.48.[6] The primary member, component A, is an evolved bright giant with a stellar classification of kA5hF0mF5 II.[3] 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.[12] It is an evolved Am star of the ρ Puppis type, a class of evolved stars showing the Am chemical peculiarities.[13] It is located in the instability strip of the Hertzsprung–Russell diagram but is not thought to be variable.[7]
With φ, h, υ, θ, e, and f, it composed the Arabic asterism Sarīr Banāt al-Na'sh, the Throne of the daughters of Na'sh, and Al-Haud, the Pond.[14] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al-Haud were the title for seven stars : fasAlhaud I, this star (τ) as Alhaud II, easAlhaud III, hasAlhaud IV, θasAlhaud V, υasAlhaud VI and φasAlhaud VII .[15]
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