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Iota Aquarii
	Location of ι Aquarii (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Aquarius
Right ascension	22h 06m 26.22742s
Declination	–13° 52′ 10.8615″
Apparent magnitude (V)	4.279
Characteristics
Spectral type	B8 V
U−B color index	–0.288
B−V color index	–0.062
Variable type	constant
Astrometry
Radial velocity (Rv)	–10.0 km/s
Proper motion (μ)	RA: +36.89 mas/yr ; Dec.: –58.99 mas/yr
Parallax (π)	18.62 ± 0.22 mas
Distance	175 ± 2 ly ; (53.7 ± 0.6 pc)
Absolute magnitude (MV)	+0.64
Details
A
Mass	3.20+0.20; −0.16 M☉
Radius	2.7 R☉
Luminosity	74 L☉
Surface gravity (log g)	4.09±0.08 cgs
Temperature	11,284±284 K
Metallicity [Fe/H]	−0.08±0.12 dex
Rotational velocity (v sin i)	135 km/s
Age	124+37; −62 Myr
B
Mass	1.00±0.03 M☉
Temperature	5,710±112 K
Metallicity [Fe/H]	−0.5 dex
Rotational velocity (v sin i)	20 km/s
Other designations
	ι Aqr, 33 Aquarii, BD–14 6209, FK5 828, HD 209819, HIP 109139, HR 8418, SAO 164861
Database references
SIMBAD	data

Iota Aquarii, Latinised from ι Aquarii, is the Bayer designation for a binary star^[7] system in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent magnitude of +4.279.^[2] Based upon parallax measurements made during the Hipparcos mission, 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.^[5]

The binary nature of this system was reported in 2009 following a radial velocity survey using the HARPS instrument.^[4] A 2010 infrared search for companions around this star was unsuccessful.^[12] 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.^[7]

The spectrum of the primary, component A, fits a stellar classification of B8 V,^[3] showing that this is a B-type main-sequence star. It is roughly 124^[7] million years old and is spinning rapidly with a projected rotational velocity of 135 km/s.^[10] The star has 3.2^[7] times the mass of the Sun and 2.7^[8] times the Sun's radius. It is radiating 74^[6] times the luminosity of the Sun from its photosphere at an effective temperature of ~11,284 km/s.^[8] The secondary, component B, has a spectrum of a solar-mass star.^[7] The system is a source for X-ray emission.^[13]

References

^ ^a ^b ^c ^d ^e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
^ ^a ^b ^c ^d ^e Kozok, J. R. (September 1985), "Photometric observations of emission B-stars in the southern Milky Way", Astronomy and Astrophysics Supplement Series, 61: 387–405, Bibcode:1985A&AS...61..387K.
^ ^a ^b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1988mcts.book.....H.
^ ^a ^b Lagrange, A. -M.; et al. (2009), "Extrasolar planets and brown dwarfs around A-F type stars. VI. High precision RV survey of early type dwarfs with HARPS", Astronomy & Astrophysics, 495 (1): 335–352, arXiv:0809.4636, Bibcode:2009A&A...495..335L, doi:10.1051/0004-6361:200810105, S2CID 62894956.
^ ^a ^b Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veroeffentlichungen des Astronomischen Rechen-Instituts Heidelberg, 35 (35), Astronomisches Rechen-Institut Heidelberg: 1, Bibcode:1999VeARI..35....1W.
^ ^a ^b ^c Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ ^a ^b ^c ^d ^e ^f Gullikson, Kevin; et al. (August 2016), "The Close Companion Mass-ratio Distribution of Intermediate-mass Stars", The Astronomical Journal, 152 (2): 13, arXiv:1604.06456, Bibcode:2016AJ....152...40G, doi:10.3847/0004-6256/152/2/40, S2CID 119179065, 40.
Note: the observations were made on modified Julian dates 6447.91 and 6524.67, which are separated by 76.76 days.
^ ^a ^b ^c ^d Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society, 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601.
^ ^a ^b Wu, Yue; et al. (January 2011), "Coudé-feed stellar spectral library - atmospheric parameters", Astronomy and Astrophysics, 525: A71, arXiv:1009.1491, Bibcode:2011A&A...525A..71W, doi:10.1051/0004-6361/201015014, S2CID 53480665.
^ ^a ^b Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.
^ "* iot Aqr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-06-30.
^ Ehrenreich, D.; et al. (November 2010), "Deep infrared imaging of close companions to austral A- and F-type stars", Astronomy and Astrophysics, 523: A73, arXiv:1007.0002, Bibcode:2010A&A...523A..73E, doi:10.1051/0004-6361/201014763, S2CID 54913363.
^ Haakonsen, Christian Bernt; Rutledge, Robert E. (September 2009), "XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources", The Astrophysical Journal Supplement, 184 (1): 138–151, arXiv:0910.3229, Bibcode:2009ApJS..184..138H, doi:10.1088/0067-0049/184/1/138, S2CID 119267456.