Eta Delphini

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Eta Gruis
Diagram showing star positions and boundaries of the Delphinus constellation and its surroundings
Cercle rouge 100%.svg
Location of η Delphini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Delphinus
Right ascension 20h 33m 57.04099s[1]
Declination +13° 01′ 38.1437″[1]
Apparent magnitude (V) 5.38[2]
Spectral type A3 IVs[3]
U−B color index +0.05[2]
B−V color index +0.08[2]
Radial velocity (Rv) −25.00±4.2[4] km/s
Proper motion (μ) RA: +73.15[1] mas/yr
Dec.: +24.66[1] mas/yr
Parallax (π) 13.81 ± 1.17[1] mas
Distance 240 ± 20 ly
(72 ± 6 pc)
Absolute magnitude (MV) +1.11[5]
Mass 2.12[6] M
Radius 2.2[7] R
Luminosity 35[8] L
Surface gravity (log g) 4.38[6] cgs
Temperature 9,355±318[6] K
Metallicity [Fe/H] +0.56[5] dex
Rotational velocity (v sin i) 65[8] km/s
Age 309[6] Myr
Other designations
η Del, 3 Del, BD+12° 4378, GC 28617, HD 195943, HIP 101483, HR 7858, SAO 106248[9]
Database references

Eta Delphini, Latinized from η Delphini, is a candidate astrometric binary[10] star system in the northern constellation of Delphinus. It has an apparent magnitude of about 5.4, meaning that it is faintly visible to the naked eye. Based upon a parallax measurement of 13.81[1] mas made by the Hipparcos spacecraft, this star is around 240 light years away from the Sun. It is advancing in general direction of the Earth with a radial velocity of −25 km/s.[4]

The stellar classification of the visible component is A3 IVs,[3] which matches an A-type subgiant star with narrow absorption lines.[11] It is a suspected chemically peculiar star[12] that is about 64.3%±9.2% of the way through its main sequence lifetime.[8] SIMBAD lists this star as a variable star,[9] although it is not catalogued as such in the GCVS.[13] It has more than double the mass[6] and radius[7] of the Sun, and is radiating 35[8] times the Sun's luminosity from its photosphere at an effective temperature of around 9,355 K.[6]


  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:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c Feinstein, A. (1974), "Photoelectric UBVRI observations of AM stars", Astronomical Journal, 79: 1290, Bibcode:1974AJ.....79.1290F, doi:10.1086/111675. 
  3. ^ a b Cowley, A.; et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal, 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819. 
  4. ^ 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:1606.08053Freely accessible, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065. 
  5. ^ a b Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971Freely accessible, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015. 
  6. ^ a b c d e f 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:1501.03154Freely accessible, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146. 
  7. ^ a b Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (Third ed.), 367: 521–524, arXiv:astro-ph/0012289Freely accessible, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451. 
  8. ^ a b c d Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052Freely accessible, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691. 
  9. ^ a b "eta Del". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-18. 
  10. ^ 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:0806.2878Freely accessible, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x. 
  11. ^ Allen, J. S., "The Classification of Stellar Spectra", Department of Physics and Astronomy: Astrophysics Group, University College London, retrieved 1 January 2014. 
  12. ^ Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788. 
  13. ^ Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80−88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085.