SU Cygni is a triple star system in the northern constellation of Cygnus, abbreviated SU Cyg. The primary component of the system is a classical Cepheid variable with a period of 3.84559 days. The changing luminosity of this star causes the system to vary in brightness from a peak apparent visual magnitude of 6.44 down to magnitude 7.22 over the course of its cycle.[3] The distance to this system is approximately 3,000 light years based on parallax measurements, and is the most accurate distance among Cepheids.[7] It is a member of the Turner 9 open cluster of stars.[11]
The variable luminosity of this star was announced by G. Müller and G. Kempf in 1898.[12] The following year, M. Luizet determined a period of 3.846 days.[13] In 1906, the radial velocity of this star was found to be variable by J. D. Maddrill, with its cycle matching the luminosity period but trailing in phase by half a day.[14] By 1916 it was classified as a Cepheid variable, with spectrographic studies showing that the spectral type varied over the course of each cycle. It ranged from a class of A6 near peak luminosity down to F7 at minimum.[15]
^ abcdefGallenne, A.; Evans, N. R.; Kervella, P.; Monnier, J. D.; Proffitt, C. R.; Schaefer, G. H.; Winston, E. M.; Kuraszkiewicz, J.; Mérand, A. (2024-11-15), Multiplicity of Galactic Cepheids from long-baseline interferometry V. High-accuracy orbital parallax and mass of SU Cygni, arXiv:2411.06647
^Maddrill, J. D. (August 1906), "Note on the variable radial velocity and the period of SU Cygni", Publications of the Astronomical Society of the Pacific, 18 (109): 252–253, Bibcode:1906PASP...18..252M, doi:10.1086/121692, S2CID119576552.
^Madore, B. F. (March 1977), "The frequency of Cepheids with companions: a photoelectric approach", Monthly Notices of the Royal Astronomical Society, 178 (3): 505–511, Bibcode:1977MNRAS.178..505M, doi:10.1093/mnras/178.3.505.
^Imbert, M. (December 1984), "Determination de rayons de cepheides. III. Vitesses radiales, orbite spectroscopique et dimension de SU Cyg", Astronomy and Astrophysics Supplement Series (in French), 58: 529–536, Bibcode:1984A&AS...58..529I.
^Evans, N. R.; et al. (March 1985), "Ultraviolet Observations of the System Containing the Cepheid SU Cyg", Bulletin of the American Astronomical Society, 17: 559, Bibcode:1985BAAS...17..559E.
^Wahlgren, G. M.; Evans, N. R. (April 1998), "A HgMn companion to the Cepheid SU Cyg", Astronomy and Astrophysics, 332: L33 –L36, Bibcode:1998A&A...332L..33W.
Further reading
Turner, David G.; et al. (June 1998), "A Search for the Parent Cluster of the Cepheid SU Cygni", Journal of the Royal Astronomical Society of Canada, 92: 145, Bibcode:1998JRASC..92..145T.
Turner, David G.; et al. (June 1997), "Galactic Clusters with Associated Cepheid Variables. V. The Case of SU Cygni", The Astronomical Journal, 113: 2104, Bibcode:1997AJ....113.2104T, doi:10.1086/118422.
Evans, Nancy Remage; Bolton, C. T. (June 1990), "The Mass of the Classical Cepheid SU Cygni", Astrophysical Journal, 356: 630, Bibcode:1990ApJ...356..630E, doi:10.1086/168869.
Remage Evans, N.; Arellano Ferro, A. (September 1986), "The luminosities of the binary cepheids SU Cyg, SU CAS and W Sgr", ESA Proceedings of an International Symposium on New Insights in Astrophysics. Eight Years of UV Astronomy with IUE, vol. 263, pp. 403–404, Bibcode:1986ESASP.263..403R.
Schneider, M. (1967), "Étude spectrophotométrique de Céphéide SU Cyg", Journal des Observateurs (in French), 50: 419, Bibcode:1967JO.....50..419S.
Hellerich, J. (November 1919), "Ableitung Spektroskopischer Bahnelemente für S Sagittae und SU Cygni", Astronomische Nachrichten (in German), 210 (5): 65, Bibcode:1919AN....210...65H, doi:10.1002/asna.19202100502.
