Iota Aquarii

Iota Aquarii is a binary star^[12][9] system in the equatorial constellation of Aquarius. Its identifier is a Bayer designation that is Latinised from ι Aquarii, and abbreviated Iota Aqr or ι Aqr. This star is visible to the naked eye with an apparent magnitude of +4.279.^[3] Based upon parallax measurements, the distance to this star is around 175 light-years (54 parsecs).^[2] The system is drifting closer to the Sun with a radial velocity of −10 km/s.^[7]

ConstellationAquarius^[1]

Right ascension22^h 06^m 26.227^s[2]

Declination−13° 52′ 10.85″^[2]

Apparentmagnitude(V)4.279^[3]

Quick facts Constellation, Right ascension ...

Iota Aquarii

Location of ι Aquarii (circled)
Observation data Epoch J2000      Equinox ICRS
Constellation	Aquarius[1]
Right ascension	22h 06m 26.227s[2]
Declination	−13° 52′ 10.85″[2]
Apparent magnitude (V)	4.279[3]
Characteristics
Evolutionary stage	main sequence[4]
Spectral type	B8 V[5]
U−B color index	−0.288[3]
B−V color index	−0.062[3]
Variable type	constant[6]
Astrometry
Radial velocity (Rv)	−10.0[7] km/s
Proper motion (μ)	RA: +42.210 mas/yr[2] Dec.: −56.566 mas/yr[2]
Parallax (π)	18.62±0.22 mas[8]
Distance	175 ± 2 ly (53.7 ± 0.6 pc)
Absolute magnitude (MV)	+0.64[1]
Details
A
Mass	2.9[9] M☉
Radius	2.1[9] R☉
Luminosity	74[1] L☉
Surface gravity (log g)	4.09±0.08[10] cgs
Temperature	11,700[9] K
Metallicity [Fe/H]	−0.08±0.12[10] dex
Rotational velocity (v sin i)	135[11] km/s
Age	70[9] Myr
B
Mass	1.2[9] M☉
Radius	1.1[9] R☉
Temperature	6,350[9] K
Metallicity [Fe/H]	−0.5[12] dex
Rotational velocity (v sin i)	20[12] km/s
Other designations
ι Aquarii, ι Aqr, 33 Aquarii, BD−14 6209, FK5 828, GC 30914, HD 209819, HIP 109139, HR 8418, SAO 164861, PPM 239801[13]
Database references
SIMBAD	data

Close

Iota Aquarii was first catalogued in Uranometria in 1603; the binary nature of this system was discovered in 2009 following a radial velocity survey using the HARPS instrument.^[6] A 2010 infrared search for companions around this star was unsuccessful.^[14] The presence of a stellar companion was confirmed through direct spectral detection in 2016. The companion shows a significant velocity variation over a 77-day interval, suggesting a short orbital period.^[12] The companion was re-observed in 2024, showing a projected separation of 0.38 astronomical units. Together with the masses of the components, this suggests an orbital period of roughly 40 days.^[9]

The spectrum of the primary, component A, fits a stellar classification of B8 V,^[5] suggesting that this is a B-type main-sequence star. It is roughly 70 million years old^[9] and is spinning rapidly with a projected rotational velocity of 135 km/s.^[11] The star has 2.9 times the mass of the Sun and 2.1 times the Sun's radius.^[9] It is radiating 74^[1] times the luminosity of the Sun from its photosphere at an effective temperature of 11,700 K.^[9] The secondary, component B, has 1.2 times the mass of the Sun, 1.1 times the radius, and an effective temperature of 6,350 K.^[9] The system is a source for X-ray emission.^[15]

There is evidence for a third companion based on the difference of proper motion measurements by the Hipparcos and Gaia spacecraft. Such a companion would have an orbital period of roughly one year, and be either a faint red dwarf or a white dwarf.^[9]