Alpha Delphini

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α Delphini A
Delphinus constellation map.svg
Red circle.svg
Location of α Delphini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Delphinus
Right ascension 20h 39m 38.28720s[1]
Declination +15° 54′ 43.4637″[1]
Apparent magnitude (V) +3.777[2] (3.86 + 6.43[3])
Spectral type B9 IV[4]
U−B color index −0.205[2]
B−V color index −0.061[2]
Radial velocity (Rv)−3.40[5] km/s
Proper motion (μ) RA: 53.82 ± 0.43[1] mas/yr
Dec.: 8.47 ± 0.31[1] mas/yr
Parallax (π)12.85 ± 0.44[1] mas
Distance254 ± 9 ly
(78 ± 3 pc)
Absolute magnitude (MV)−0.4[6]
Period (P)17.0 yr
Semi-major axis (a)0.158″
Eccentricity (e)0.47
Inclination (i)160°
Longitude of the node (Ω)99°
Periastron epoch (T)1983.80
Argument of periastron (ω)
α Del Aa
Mass2.82[3] M
Radius3.92[8] R
Surface gravity (log g)3.93[9] cgs
Temperature11,643[9] K
Rotational velocity (v sin i)144[9] km/s
Age227[9] Myr
Other designations
α Del, 9 Delphini, BD+15 4222, HD 196867, HIP 101958, HR 7906, SAO 106357, CCDM J20396+1555, WDS J20396+1555
Database references

Alpha Delphini (α Delphini, abbreviated Alpha Del, α Del) is a multiple star system in the constellation of Delphinus.

It consists of a binary star, designated Alpha Delphini A, together with five faint, probably optical companions,[10][11] designated Alpha Delphini B, C, D, E and F. A's two components are themselves designated Alpha Delphini Aa (officially named Sualocin /ˈswɒlsɪn/, the historical name for the entire system)[12][13] and Ab.[10]


α Delphini (Latinised to Alpha Delphini) is the system's Bayer designation. The designations of the six constituents as Alpha Delphini A to F, and those of A's components - Alpha Delphini Aa and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14]

The system bore an historical name, Sualocin, which arose as follows: Niccolò Cacciatore was the assistant to Giuseppe Piazzi, and later his successor as Director of the Palermo Observatory. The name first appeared in Piazzi's Palermo Star Catalogue. When the Catalogue was published in 1814, the unfamiliar names Sualocin and Rotanev were attached to Alpha and Beta Delphini, respectively. Eventually the Reverend Thomas Webb, a British astronomer, puzzled out the explanation.[15] Cacciatore's name, Nicholas Hunter in English translation, would be Latinized to Nicolaus Venator. Reversing the letters of this construction produces the two star names. They have endured, the result of Cacciatore's little practical joke of naming the two stars after himself.[16]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[17] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[18] It approved the name Sualocin for the component Alpha Delphini Aa on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[13]

In Chinese, 瓠瓜 (Hù Guā), meaning Good Gourd, refers to an asterism consisting of Alpha Delphini, Gamma2 Delphini, Delta Delphini, Beta Delphini and Zeta Delphini.[19] Consequently, the Chinese name for Alpha Delphini itself is 瓠瓜一 (Hù Guā yī, English: the First Star of Good Gourd).[20]

In Hindu astronomy, the star corresponded to one of the nakshatras named Dhanishta.


Alpha Delphini A is a spectroscopic binary star which has now been resolved using speckle interferometry. The components are separated by 0.2" and have a 17-year orbit. Alpha Delphini Aa has a spectral type of B9IV. The spectral type of the secondary star cannot be determined as it is too close and too faint compared to the primary, and its other properties are also unknown. The primary is a subgiant that has begun to evolve away from the main sequence. It is 2.82 times as massive as the sun and about twice as hot.

The five faint companions have visual magnitudes around 11th to 13th magnitude and separations of 35" to 72". They all show motion relative to Alpha Delphini A.[10][11]


  1. ^ a b c d e van Leeuwen, F. (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.Vizier catalog entry
  2. ^ a b c Oja, T. (1991). "UBV photometry of stars whose positions are accurately known. VI". Astronomy and Astrophysics Supplement Series. 89: 415. Bibcode:1991A&AS...89..415O.
  3. ^ a b Malkov, O. Yu.; Tamazian, V. S.; Docobo, J. A.; Chulkov, D. A. (2012). "Dynamical masses of a selected sample of orbital binaries". Astronomy & Astrophysics. 546: A69. Bibcode:2012A&A...546A..69M. doi:10.1051/0004-6361/201219774.
  4. ^ Morgan, W. W.; Keenan, P. C. (1973). "Spectral Classification". Annual Review of Astronomy and Astrophysics. 11: 29–50. Bibcode:1973ARA&A..11...29M. doi:10.1146/annurev.aa.11.090173.000333.
  5. ^ Kharchenko, N. V.; Scholz, R.-D.; Piskunov, A. E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ˜55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. S2CID 119323941.
  6. ^ Jaschek, C.; Gomez, A. E. (1998). "The absolute magnitude of the early type MK standards from HIPPARCOS parallaxes". Astronomy and Astrophysics. 330: 619. Bibcode:1998A&A...330..619J.
  7. ^ Söderhjelm, Staffan (January 1999), "Visual binary orbits and masses post Hipparcos", Astronomy and Astrophysics, 341: 121–140, Bibcode:1999A&A...341..121S
  8. ^ Fitzpatrick, E. L.; Massa, D. (2005). "Determining the Physical Properties of the B Stars. II. Calibration of Synthetic Photometry". The Astronomical Journal. 129 (3): 1642. arXiv:astro-ph/0412542. Bibcode:2005AJ....129.1642F. doi:10.1086/427855. S2CID 119512018.
  9. ^ a b c d David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets". The Astrophysical Journal. 804 (2): 146. arXiv:1501.03154. Bibcode:2015ApJ...804..146D. doi:10.1088/0004-637X/804/2/146. S2CID 33401607.
  10. ^ a b c Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
  11. ^ a b Dommanget, J.; Nys, O. (1994). "Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition - Catalogue of the components of double and multiple stars (CCDM) first edition". Communications de l'Observatoire Royal de Belgique. 115: 1. Bibcode:1994CoORB.115....1D.
  12. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  13. ^ a b "Naming Stars". Retrieved 16 December 2017.
  14. ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  15. ^ Webb, T.W. (1859). Celestial Objects for Common Telescopes. London: Longmans, Green and Co. pp. 193–194.
  16. ^ Hurn, Mark. "Secrets of the 1814 Palermo Star Catalogue". The Story of Star Names. Mark Hurn, Institute of Astronomy Library, Univ. of Cambridge. Archived from the original on 4 March 2016. Retrieved 11 May 2015.
  17. ^ "IAU Working Group on Star Names (WGSN)". International Astronomical Union. Retrieved 22 May 2016.
  18. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  19. ^ 陳久金 (2005). 中國星座神話. 五南圖書出版股份有限公司. ISBN 978-986-7332-25-7.
  20. ^ 香港太空館 - 研究資源 - 亮星中英對照表 (in Chinese). Hong Kong Space Museum. Archived from the original on August 18, 2010. Retrieved November 23, 2010.