91 Aquarii

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For other stars named Psi Aqr, see Psi Aquarii
91 Aquarii
Diagram showing star positions and boundaries of the Aquarius constellation and its surroundings
Cercle rouge 100%.svg

Location of ψ1 Aquarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Aquarius
Right ascension 23h 15m 53.49482s[1]
Declination –9° 05′ 15.8546″[1]
Apparent magnitude (V) +4.248[2]
Spectral type K0 III[3]
U−B color index +1.035[2]
B−V color index +1.104[2]
R−I color index 0.56[4]
Radial velocity (Rv) −25.49±0.74[5] km/s
Proper motion (μ) RA: +368.78[1] mas/yr
Dec.: –17.16[1] mas/yr
Parallax (π) 21.77 ± 0.29[1] mas
Distance 150 ± 2 ly
(45.9 ± 0.6 pc)
Mass 1.74±0.35[6] M
Radius 10.16±0.45[6] R
Luminosity 49[5] L
Surface gravity (log g) 2.6[5] cgs
Temperature 4603[5] K
Metallicity [Fe/H] –0.14[5] dex
Rotational velocity (v sin i) 2.9[5] km/s
Age 1.25+0.16
[7] Gyr
Other designations
Psi1 Aquarii, ADS 16633, BD–09 6156, FK5 1608, Gl 893.2, HD 219449, HIP 114855, HR 8841, LTT 9437, SAO 146598.
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)
Database references

91 Aquarii is the Flamsteed designation for a triple star[8] system in the equatorial constellation of Aquarius. It also bears the Bayer designation Psi1 Aquarii1 Aqr, ψ1 Aquarii). It is visible to the naked eye with an apparent visual magnitude of +4.248.[2] Parallax measurements yield an estimated distance of around 150 light-years (46 parsecs) from Earth.[1] An extrasolar planet is known to orbit the main star.

Stellar system[edit]

91 Aquarii is a triple star system.[8] The primary component, 91 Aqr A, is a giant star with a stellar classification of K0 III.[3] This is an evolved star with 174% of the Sun's mass that has expanded to over 10 times the size of the Sun.[6] It is radiating 49[5] times the Sun's luminosity from its outer envelope at an effective temperature of 4,603 K.[5] This gives it the orange-hued glow of a K-type star.[9]

The primary shares a common proper motion with two others stars, 91 Aqr B and C, suggesting that they are physically connected.[10] The latter pair form a binary system located at an angular separation of 52 arcseconds from the primary.[3] They are 10th magnitude stars separated by 0.3 arcseconds from each other.

Component Apparent

A 4.22 K0 III
B 9.62 K3 V
C 10.10

Because it lies near the same line of sight, the binary star system CCDM J23159-0905DE was listed to belong to the 91 Aquarii system according to the CCDM catalogue. However, it is listed as physically unconnected in the WDS catalogue and the pair have a different proper motion than 91 Aquarii.[10] CCDM J23159-0905DE has two components, the 13th magnitude CCDM J23159-0905D 80.4 arcseconds from 91 Aquarii, and the 14th magnitude CCDM J23159-0905E 19.7 arcseconds from 91 Aquarii.

Planetary system[edit]

In 2003, the discovery of an extrasolar planet orbiting 91 Aquarii A was announced. Despite controversy, the exoplanet was confirmed again on Jan 03, 2011 by the Conference " Planetary Systems Beyond the Main Sequence", Bamberg 2010 (Quirrenbach et al.).[citation needed]

The 91 Aquarii planetary system
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b ≥ 2.9[11] MJ ≥ 0.3[11] 182[12] 0

See also[edit]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752free to read, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society, 172: 667–679, Bibcode:1975MNRAS.172..667J, doi:10.1093/mnras/172.3.667. 
  3. ^ a b c Buscombe, W. (1962), "Spectral classification of Southern fundamental stars", Mount Stromlo Observatory Mimeogram, 4, Bibcode:1962MtSOM...4....1B. 
  4. ^ VizieR Detailed Page for HR 8841, retrieved 2009-11-28. 
  5. ^ a b c d e f g h Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209. 
  6. ^ a b c Ghezzi, L.; et al. (December 2010), "Metallicities of Planet-hosting Stars: A Sample of Giants and Subgiants", The Astrophysical Journal, 725 (1): 721–733, arXiv:1008.3539free to read, Bibcode:2010ApJ...725..721G, doi:10.1088/0004-637X/725/1/721. 
  7. ^ Chanamé, Julio; Ramírez, Iván (February 2012), "Toward Precise Ages for Single Stars in the Field. Gyrochronology Constraints at Several Gyr Using Wide Binaries. I. Ages for Initial Sample", The Astrophysical Journal, 746 (1): 102, arXiv:1109.0013free to read, Bibcode:2012ApJ...746..102C, doi:10.1088/0004-637X/746/1/102 
  8. ^ a b Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878free to read, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, retrieved 2012-01-16. 
  10. ^ a b Roell, T.; Neuhäuser, R.; Seifahrt, A.; Mugrauer, M. (June 2012), "Extrasolar planets in stellar multiple systems", Astronomy & Astrophysics, 542: A92, arXiv:1204.4833free to read, Bibcode:2012A&A...542A..92R, doi:10.1051/0004-6361/201118051 
  11. ^ a b Raghavan, Deepak; et al. (July 2006), "Two Suns in The Sky: Stellar Multiplicity in Exoplanet Systems", The Astrophysical Journal, 646 (1): 523–542, arXiv:astro-ph/0603836free to read, Bibcode:2006ApJ...646..523R, doi:10.1086/504823. 
  12. ^ Mitchell, D. S.; S. Frink; A. Quirrenbach; D. A. Fischer; G. W. Marcy; R. P. Butler (2004-01-05). "Four Substellar Companions Found Around K Giant Stars". Bulletin of the American Astronomical Society, 35#5; AAS 203rd Meeting; Session 17 Extra Solar Planets. Retrieved 2009-11-28. 

External links[edit]

Coordinates: Sky map 23h 15m 53.5s, −09° 05′ 16″