Epsilon Delphini

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ε Delphini
Delphinus constellation map.svg
Red circle.svg
Location of ε Delphini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Delphinus
Right ascension 20h 33m 12.77192s[1]
Declination +11° 18′ 11.7412″[1]
Apparent magnitude (V) 4.03[2] (3.95−4.05)[3]
Spectral type B6 III[4]
U−B color index −0.46[2]
B−V color index −0.13[2]
Variable type suspected[3]
Radial velocity (Rv)−19.4±0.7[5] km/s
Proper motion (μ) RA: +11.96[1] mas/yr
Dec.: −28.97[1] mas/yr
Parallax (π)9.87 ± 0.21[1] mas
Distance330 ± 7 ly
(101 ± 2 pc)
Absolute magnitude (MV)−0.06[6]
Radius4.6[7] R
Luminosity676[8] L
Surface gravity (log g)3.71±0.09[9] cgs
Temperature13,614±15[7] K
Metallicity [Fe/H]+0.08±0.10[9] dex
Rotational velocity (v sin i)52±4[10] km/s
Other designations
Aldulfin, ε Del, 2 Del, BD+10° 4321, FK5 768, HD 195810, HIP 101421, HR 7852, SAO 106230[11]
Database references

Epsilon Delphini (ε Delphini, abbreviated Eps Del, ε Del), also named Aldulfin,[12] is a solitary,[13] blue-white hued star in the northern constellation of Delphinus. It is visible to the naked eye with an apparent visual magnitude of 4.03.[2] Based upon an annual parallax shift of 9.87 mas as seen from the Earth,[1] the system is located about 330 light-years from the Sun.

Proper names[edit]

ε Delphini (Latinised to Epsilon Delphini) is the star's Bayer designation.

The star bore the traditional Arabic name ðanab ad-dulfīn or Dzaneb al Delphin, which appeared in the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket and which was translated into Latin as Cauda Delphini, meaning 'the dolphin's tail'.[14] In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Aldulfin for this star on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[12]

In Chinese, 敗瓜 (Bài Guā), meaning Rotten Gourd, refers to an asterism consisting of Epsilon Delphini, Eta Delphini, Theta Delphini, Iota Delphini and Kappa Delphini.[16] Consequently, Epsilon Delphini itself is known as 敗瓜一 (Bài Guā yī, English: the First Star of Rotten Gourd.).[17] From this Chinese name, the name Pae Chaou was formed.[18]


At Epsilon Delphini's distance, the visual magnitude is diminished by an extinction factor of 0.11 due to interstellar dust.[6] The star is moving closer to the Sun with a radial velocity of −19 km/s.[5]

This is a B-type giant star with a stellar classification of B6 III.[4] It has 4.6[7] times the Sun's radius and is radiating 676[8] times the solar luminosity from its photosphere at an effective temperature of 13,614 K.[7] The star may be slightly variable, occasionally brightening to magnitude 3.95.[3] It is spinning with a projected rotational velocity of 52 km/s.[10]


  1. ^ a b c d e f 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.
  2. ^ a b c d Crawford, D. L.; et al. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220.
  3. ^ a b c Samus, N. N.; et al. (January 2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085.
  4. ^ a b Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179.
  5. ^ a b Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  6. ^ a b Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035.
  7. ^ 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: 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601.
  8. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  9. ^ 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.
  10. ^ a b Bailey, J. D.; Landstreet, J. D. (2013), "Abundances determined using Si ii and Si iii in B-type stars: Evidence for stratification", Astronomy & Astrophysics, 551: A30, arXiv:1301.3050, Bibcode:2013A&A...551A..30B, doi:10.1051/0004-6361/201220671.
  11. ^ "eps Del -- Variable Star", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2017-06-28.
  12. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  13. ^ 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:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  14. ^ Knobel, E. B. (June 1895), "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket", Monthly Notices of the Royal Astronomical Society, 55: 429–438, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429.
  15. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  17. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived September 29, 2009, at the Wayback Machine., Hong Kong Space Museum. Accessed on line November 23, 2010.
  18. ^ Allen, R. H. (1963), Star Names, Their Lore and Meaning (Dover ed.), p. 201, retrieved 2017-06-29.