99 Aquarii

This article is about b2 Aquarii. For other star systems with this Bayer designation, see b Aquarii.
99 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Location of 99 Aquarii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension 23h 26m 02.78566s[1]
Declination –20° 38′ 31.251″[1]
Apparent magnitude (V) 4.37[2]
Characteristics
Spectral type K4 III[3]
U−B color index +1.815[2]
B−V color index +1.431[2]
Variable type Suspected[4]
Astrometry
Radial velocity (Rv)+15.7[5] km/s
Proper motion (μ) RA: –50.72[1] mas/yr
Dec.: –64.22[1] mas/yr
Parallax (π)11.51 ± 0.21 mas[1]
Distance283 ± 5 ly
(87 ± 2 pc)
Details
Radius33[6] R☉
Surface gravity (log g)1.66[7] cgs
Temperature3980[7] K
Metallicity [Fe/H]–0.20[7] dex
Other designations
BD–21 6420, HD 220704, HIP 115669, HR 8906, NSV 14554, SAO 191900.[8]
Database references
SIMBADdata

99 Aquarii (abbreviated 99 Aqr) is a star in the equatorial constellation of Aquarius. 99 Aquarii is the Flamsteed designation, although it also bears the Bayer designation b2 Aquarii. It is visible to the naked eye with an apparent visual magnitude of 4.38;[2] according to the Bortle Dark-Sky Scale this is bright enough to be seen even from city skies under ideal viewing conditions. Based upon parallax measurements, the distance to this star is around 283 light-years (87 parsecs).[1]

This is a giant star with a stellar classification of K4 III.[3] It is a suspected variable star that apparently ranges in magnitude between 4.35 and 4.45.[4] The measured angular diameter of this star is 3.55 ± 0.21 mas.[9] At the estimated distance of Delta Ophiuchi,[1] this yields a physical size of about 33 times the radius of the Sun.[6] The outer atmosphere has an effective temperature of 3980 K,[7] giving it the orange-hued glow of a cool, K-type star.[10]

This star was a candidate member of the Ursa Major Moving Group based on the work of American astronomer Nancy Roman, but this membership is now in question.[11]

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