  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Aquila |
| Right ascension | 20h 04m 08.31506s [1] |
| Declination | +07° 16′ 40.6705″ [1] |
| Apparent magnitude (V) | 5.6799±0.0009 [2] |
| Characteristics | |
| Spectral type | K0 III [3] |
| U−B color index | +0.86 [4] |
| B−V color index | +1.06 [4] |
| Astrometry | |
| Radial velocity (Rv) | −29.27±0.13 [1] km/s |
| Proper motion (μ) | RA: +14.039 [1] mas/yr Dec.: +12.141 [1] mas/yr |
| Parallax (π) | 5.9403 ± 0.0883 mas [1] |
| Distance | 549 ± 8 ly (168 ± 3 pc) |
| Absolute magnitude (MV) | −0.24 [5] |
| Details | |
| Radius | 21.24+0.84 −1.05 [1] R☉ |
| Luminosity | 207.9±3.8 [1] L☉ |
| Surface gravity (log g) | 2.69 [3] cgs |
| Temperature | 4756+110 −92 [1] K |
| Metallicity [Fe/H] | –0.15 [3] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
Tau Aquilae, Latinized from τ Aquilae, also named Tianfu, [7] is a star in the equatorial constellation of Aquila. The apparent visual magnitude of 5.7 [2] indicates it is a faint star that is visible to the naked eye from suburban skies; at least according to the Bortle Dark-Sky Scale. The annual orbital motion of the Earth causes a parallax shift of 5.94 mas , [1] which means the distance to this star is approximately 549 light-years (168 parsecs). The magnitude of the star is diminished by 0.28 from extinction caused by interstellar gas and dust. [2] It is drifting closer to the Sun with a radial velocity of −29 km/s. [1]
The spectrum of Tau Aquilae matches a stellar classification of K0 III, [3] with the luminosity class of III suggesting this is an evolved giant star that has exhausted the supply of hydrogen at its core and left the main sequence of stars like the Sun. It has 21 [1] times the girth of the Sun and is radiating 208 times the Sun's luminosity. [1] The outer envelope is radiating energy into space with an effective temperature of 4,660 K, [3] giving it the orange hued glow of a K-type star. [8]
Tianfu (天桴) was an ancient Chinese constellation consisting of four stars. τ Aquilae was the first star of an early version of this constellation, before the Tang dynasty. The IAU Working Group on Star Names approved the name Tianfu for this star on 16 May 2024 and it is now so entered in the IAU Catalog of Star Names. [7] (See also θ Aquilae.)
