Eta Aquarii

Eta Aquarii is a star in the equatorial constellation of Aquarius. Its identifier is a Bayer designation that is Latinized from η Aquarii, and abbreviated Eta Aqr or η Aqr, respectively. The star is visible to the naked eye with an apparent visual magnitude of 4.04.^[2] The distance to this star, as determined by parallax measurements, is about 168 light-years (52 parsecs).^[1] It is drifting closer to the Sun with a radial velocity of –8 km/s.^[2] Eta Aquarii is near the radiant of a meteor shower named after it.

Eta Aquarii

Location of η Aquarii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Aquarius
Right ascension	22h 35m 21.38126s[1]
Declination	−00° 07′ 02.9888″[1]
Apparent magnitude (V)	4.04[2]
Characteristics
Spectral type	B9IV-Vn[3] or B8/9V[4]
U−B color index	−0.28[5]
B−V color index	−0.10[5]
Astrometry
Radial velocity (Rv)	–8.0[2] km/s
Proper motion (μ)	RA: +89.74 mas/yr[1] Dec.: −56.10 mas/yr[1]
Parallax (π)	19.43±0.25 mas[1]
Distance	168 ± 2 ly (51.5 ± 0.7 pc)
Absolute magnitude (MV)	0.31±0.15[6]
Details[6]
Mass	2.96±0.04 M☉
Radius	2.77±0.30 R☉
Luminosity	102.8 L☉
Surface gravity (log g)	4.02±0.04 cgs
Temperature	11,042±301 K
Rotational velocity (v sin i)	271±32 km/s
Age	65[7] Myr
Other designations
η Aquarii, η Aqr, Eta Aqr, 62 Aquarii, AG−00 2882, BD−00 4384, FK5 850, HD 213998, HIP 111497, HR 8597, SAO 146181, PPM 181490[8]
Database references
SIMBAD	data

The stellar classification of Eta Aquarii is B9IV-Vn,^[3] which may indicate that it is beginning to evolve away from the main sequence into a subgiant as the supply of hydrogen at its core becomes exhausted. It is 65^[7] million years old and is spinning rapidly with a high projected rotational velocity of 271 km/s.^[6] This rotation is causing an equatorial bulge, giving the star an oblate figure with a 24% larger radius at the equator than at the poles.^[9] The Doppler effect from the rapid rotation is causing the absorption lines in the star's spectrum to blur, as indicated by the 'n' suffix in the star's classification. Eta Aquarii has an estimated 2.96 times the mass of the Sun and 2.8 times the Sun's radius. The star is radiating 103 times the luminosity of the Sun from its photosphere at an effective temperature of 11,042 K.^[6]

Naming

This star, along with γ Aqr (Sadachbia), π Aqr (Seat) and ζ Aqr (Sadaltager / Achr al Achbiya), were al Aḣbiyah (الأخبية), the Tent.^[10][11]

In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of η Aquarii, γ Aquarii, ζ Aquarii, π Aquarii.^[12] Consequently, the Chinese name for η Aquarii itself is 墳墓三 (Fén Mù sān, English: the Third Star of Tomb.)^[13]