81 Aquarii

81 Aquarii is a star in the constellation of Aquarius. It has an orange hue and is barely visible to the naked eye with an apparent visual magnitude of 6.23.^[2] 81 Aquarii is its Flamsteed designation. The star is located at a distance of approximately 451 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +1.6 km/s.^[1] It is positioned near the ecliptic and thus is subject to lunar occultations.^[5]

81 Aquarii

Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius
Right ascension	23h 01m 23.64174s[1]
Declination	−07° 03′ 40.1556″[1]
Apparent magnitude (V)	6.23[2]
Characteristics
Spectral type	K5 III[3]
B−V color index	1.418±0.005[2]
Astrometry
Radial velocity (Rv)	+1.59±0.14[1] km/s
Proper motion (μ)	RA: −16.221±0.139[1] mas/yr Dec.: −7.911±0.087[1] mas/yr
Parallax (π)	7.2372±0.0691 mas[1]
Distance	451 ± 4 ly (138 ± 1 pc)
Absolute magnitude (MV)	0.34[2]
Details
Radius	18.02+1.36 −2.45[1] R☉
Luminosity	102.3+1.3 −0.6[1] L☉
Temperature	4,324+329 −154[1] K
Other designations
81 Aqr, BD−07°5910, HD 217531, HIP 113674, HR 8757, SAO 146447[4]
Database references
SIMBAD	data

This is an aging giant star with a stellar classification of K5 III,^[3] indicating it has exhausted the supply of hydrogen at its core then cooled and expanded off the main sequence. The stellar spectrum displays strong lines of cyanogen.^[6] It presently has 18 times the radius of the Sun and is radiating 102 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,324 K.^[1]