Xi Aquilae

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Xi Aquilae
Diagram showing star positions and boundaries of the Aquila constellation and its surroundings
Cercle rouge 100%.svg

Location of ξ Aquilae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Aquila
Right ascension 19h 54m 14.88184s[1]
Declination +08° 27′ 41.2299″[1]
Apparent magnitude (V) 4.722[2]
Spectral type G9 III[3]
U−B color index +0.89[4]
B−V color index +1.049[5]
R−I color index 0.57
Radial velocity (Rv) -42.10 ± 0.14[5] km/s
Proper motion (μ) RA: +101.91[1] mas/yr
Dec.: –81.20[1] mas/yr
Parallax (π) 17.77 ± 0.29[1] mas
Distance 184 ± 3 ly
(56.3 ± 0.9 pc)
Mass 1.16 ± 0.28[6] M
Radius 10.45 ± 0.18[7] R
Luminosity 49[6] L
Surface gravity (log g) 2.66[6] cgs
Temperature 4,783[6] K
Metallicity [Fe/H] –0.13[6] dex
Rotational velocity (v sin i) 5.2[5] km/s
Age 4.63 ± 2.88[6] Gyr
Other designations
BD+08 4261, 59 Aquilae, HD 188310, HIP 97938, HR 7595, SAO 125210.[8]

Xi Aquilae (ξ Aql, ξ Aquilae) is the Bayer designation for a star in the equatorial constellation of Aquila. It is a red clump giant star with an apparent magnitude of 4.7[2] and is located at a distance of 184 light-years (56 parsecs) from Earth.[1] As of 2008, an extrasolar planet has been confirmed in orbit around the star.[9]


This star has an apparent visual magnitude of 4.722,[2] which, according to the Bortle Dark-Sky Scale, is bright enough to be viewed with the naked eye from dark suburban skies. The orbital motion of the Earth causes this star to undergo an annual parallax shift of 17.77 milliarcseconds. From this measurement, the distance to this star can be determined, yielding an estimate of approximately 184 light years with a 2% margin of error.[1] The magnitude of the star is diminished by 0.09 from the extinction caused by interstellar gas and dust.[6]

The spectrum of this star matches a stellar classification of G9 III,[3] where the G9 means that it belongs to the category of G-type stars while the luminosity class of III indicates that, at an estimated age of nearly five billion years,[6] is an evolved star that has reached the giant stage. It is in the red clump,[10] meaning it is generating energy through the fusion of helium into carbon at its core.

Xi Aquilae has an estimated 116% of the Sun's mass,[6] while its outer atmosphere has expanded to more than ten times the radius of the Sun.[7] It is radiating 49 times the Sun's luminosity at an effective temperature of 4,783 K,[6] giving it the golden-hued glow of a G-type star.[11] The possibility of a binary stellar companion can been ruled out based upon observations with the CHARA array.[3]

Planetary system[edit]

In 2008, the presence of a planetary companion was announced, based upon Doppler spectroscopy results from the Okayama Astrophysical Observatory. This object, designated as Xi Aquilae b, has at least 2.8 Jupiter masses and is orbiting at an estimated 0.68 astronomical units from the star with a period of 136.75 days.[9] Any planets that once orbited to the interior of this object may have been consumed as the star entered the red giant stage and expanded in radius.[12]

The Xi Aquilae planetary system[9]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b >2.8 MJ 0.68 136.75 ± 0.25 0 (fixed)

The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[13][14] The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.[15]


  1. ^ a b c d e f g 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. 
  2. ^ a b c Soubiran, C.; Le Campion, J.-F.; Cayrel de Strobel, G.; Caillo, A. (June 2010), "The PASTEL catalogue of stellar parameters", Astronomy and Astrophysics 515: A111, arXiv:1004.1069, Bibcode:2010A&A...515A.111S, doi:10.1051/0004-6361/201014247. 
  3. ^ a b c Baines, Ellyn K.; et al. (July 2010), "Ruling Out Possible Secondary Stars to Exoplanet Host Stars Using the CHARA Array", The Astronomical Journal 140 (1): 167–176, arXiv:1005.2930, Bibcode:2010AJ....140..167B, doi:10.1088/0004-6256/140/1/167. 
  4. ^ Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J. 
  5. ^ a b c 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 d e f g h i j 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:1008.3539, Bibcode:2010ApJ...725..721G, doi:10.1088/0004-637X/725/1/721. 
  7. ^ a b Baines, Ellyn K.; et al. (August 2009), "Eleven Exoplanet Host Star Angular Diameters from the Chara Array", The Astrophysical Journal 701 (1): 154–162, arXiv:0906.2702, Bibcode:2009ApJ...701..154B, doi:10.1088/0004-637X/701/1/154. 
  8. ^ "ksi Aql -- Star", SIMBAD Astronomical Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-07-20. 
  9. ^ a b c Sato, Bun'ei; et al. (2008). "Planetary Companions around Three Intermediate-Mass G and K Giants: 18 Delphini, ξ Aquilae and HD 81688". Publications of the Astronomical Society of Japan 60 (3): 539–550. arXiv:0802.2590. Bibcode:2008PASJ...60..539S. doi:10.1093/pasj/60.3.539. 
  10. ^ Puzeras, E.; et al. (October 2010), "High-resolution spectroscopic study of red clump stars in the Galaxy: iron-group elements", Monthly Notices of the Royal Astronomical Society 408 (2): 1225–1232, arXiv:1006.3857, Bibcode:2010MNRAS.408.1225P, doi:10.1111/j.1365-2966.2010.17195.x. 
  11. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16. 
  12. ^ Kunitomo, M.; et al. (August 2011), "Planet Engulfment by ~1.5-3 M sun Red Giants", The Astrophysical Journal 737 (2): 66, arXiv:1106.2251, Bibcode:2011ApJ...737...66K, doi:10.1088/0004-637X/737/2/66. 
  13. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. IAU.org. 9 July 2014
  14. ^ NameExoWorlds.
  15. ^ NameExoWorlds.

External links[edit]

Coordinates: Sky map 19h 54m 15s, +08° 27′ 41″