Epoch J2000 Equinox J2000
|Right ascension||19h 42m 34.00828s|
|Declination||+11° 49′ 35.7023″|
|Apparent magnitude (V)||5.292 (5.80/6.68)|
|Spectral type||G2 Ib-II + B5 V|
|U−B color index||+0.01|
|B−V color index||+0.56|
|Radial velocity (Rv)||-19.2 km/s|
|Proper motion (μ)|| RA: 1.75 mas/yr |
Dec.: -10.11 mas/yr
|Parallax (π)||3.82 ± 0.51 mas|
|Distance||approx. 900 ly |
(approx. 260 pc)
|Absolute magnitude (MV)||−1.53 (−2.1 + −1)|
|Rotational velocity (v sin i)||3.6 km/s|
Chi Aquilae (χ Aql, χ Aquilae) is the Bayer designation for a binary star in the equatorial constellation of Aquila, the eagle. This system is bright enough to be seen with the naked eye at a combined visual magnitude of +5.29. Based upon parallax measurements made during the Hipparcos mission, Chi Aquilae is at a distance of approximately 900 light-years (280 parsecs) from Earth.
The two components of χ Aquilae can be separated in the spectrum and their relative brightness has been measured, but their other properties are uncertain. The cool component is a G2 bright giant or supergiant and is visually brighter than the hot component, so it is treated as the primary. The hot component is a late B or A type star, presumed to be a main sequence star.
The observed spectrum of the primary star is G2 Ib, a yellow supergiant. It is calculated to have an absolute magnitude of −2.1. The secondary is observed to have a spectral type of B5.5 and is expected to be a main sequence star with an absolute magnitude of −1. However, the brightness difference between a G2 supergiant and a B5.5 dwarf is expected to be larger. It is unclear whether the primary is not a supergiant or the secondary is brighter than a main sequence star.
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