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Binary star in the constellation Ursa Major From Wikipedia, the free encyclopedia
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.[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]
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Ursa Major |
Right ascension | 09h 10m 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 | |
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.[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 : f as Alhaud I, this star (τ) as Alhaud II, e as Alhaud III, h as Alhaud IV, θ as Alhaud V, υ as Alhaud VI and φ as Alhaud VII .[15]
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