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SU Cygni

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SU Cygni

A light curve for SU Cygni, plotted from TESS data[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 19h 44m 48.734s[2]
Declination 29° 15′ 52.90″[2]
Apparent magnitude (V) 6.44 to 7.22[3]
Characteristics
Spectral type F2Iab: + B8.0V + A0V:[4][5]
Variable type δ Cep[3]
Astrometry
Radial velocity (Rv)−21.5±2.4[6] km/s
Proper motion (μ) RA: 0.107 mas/yr[2]
Dec.: −3.247 mas/yr[2]
Parallax (π)1.0275 ± 0.0522 mas[2]
Distance3,200 ± 200 ly
(970 ± 50 pc)
Orbit[7]
PrimarySU Cyg A
CompanionSU Cyg B
Period (P)549.24±0.02 d
Eccentricity (e)0.350+0.004
−0.003
Periastron epoch (T)2,443,766.2±1.1 HJD
Argument of periastron (ω)
(secondary)		223.85±0.85°
Semi-amplitude (K1)
(primary)		29.83±0.15 km/s
Details
Primary
Mass4.7[4] M☉
Radius43.9[8] R☉
Luminosity1,349[4] L☉
Surface gravity (log g)2.1–2.4[9] cgs
Temperature5,956 to 6,314[9] K
Metallicity [Fe/H]−0.03±0.04[7] dex
Secondary
Mass4.7±0.7[10] M☉
Other designations
SU Cyg, BD+28°3460, GC 27336, HD 186688, HIP 97150, HR 7518, SAO 87659, PPM 109630, WDS J19448+2916Aa,Ab[11]
Database references
SIMBADdata

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 3.8455473 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 3,200 light years based on parallax measurements.[2] It is a member of the Turner 9 open cluster of stars.[10]

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]

A companion star, designated component B, was detected photometrically by B. F. Madore in 1977,[16] with the colors suggesting a B-type main-sequence star with a class of B6–7V. This finding was supported by observations of J. D. Fernie in 1979, who determined a class of B6V. In 1984, M. Imbert measured an orbital period of 549.2 days for the pair, with an orbital eccentricity (ovalness) of 0.35.[8] Ultraviolet observations with the IUE spacecraft in 1985 showed that the companion is a close binary system with a period of 4.7 days. The members of this pair have classes of B8 and A0.[17] In 1998, the B-type companion was found to be a chemically peculiar HgMn star.[18]

There is a candidate comoving companion star located at an angular separation of 24″ to the west of SU Cyg. It is an A-type main-sequence star with a class of A2V. This star does not appear to be gravitationally bound to SU Cyg.[10]

References

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  1. ^ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 6 January 2023.
  2. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. ^ a b c Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 125853869.
  4. ^ a b c Evans, Nancy Remage; et al. (October 2013), "Binary Cepheids: Separations and Mass Ratios in 5 M⊙ Binaries", The Astronomical Journal, 146 (4): 93, arXiv:1307.7123, Bibcode:2013AJ....146...93E, doi:10.1088/0004-6256/146/4/93, S2CID 34133110, 93.
  5. ^ Eggleton, Peter P.; Yakut, Kadri (July 2017), "Models for 60 double-lined binaries containing giants", Monthly Notices of the Royal Astronomical Society, 468 (3): 3533–3556, arXiv:1611.05041, Bibcode:2017MNRAS.468.3533E, doi:10.1093/mnras/stx598.
  6. ^ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35493 Hipparcos Stars", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
  7. ^ a b Groenewegen, M. A. T. (2008), "Baade-Wesselink distances and the effect of metallicity in classical cepheids", Astronomy and Astrophysics, 488 (1): 25–35, arXiv:0807.1269, Bibcode:2008A&A...488...25G, doi:10.1051/0004-6361:200809859, S2CID 13871801.
  8. ^ a b 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.
  9. ^ a b Andrievsky, S. M.; et al. (2013), "Barium abundances in Cepheids", Monthly Notices of the Royal Astronomical Society, 428 (4): 3252, arXiv:1210.6211, Bibcode:2013MNRAS.428.3252A, doi:10.1093/mnras/sts270.
  10. ^ a b c Kervella, Pierre; et al. (March 2019), "Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2. II. Resolved common proper motion pairs", Astronomy & Astrophysics, 623: 40, arXiv:1908.00545, Bibcode:2019A&A...623A.117K, doi:10.1051/0004-6361/201834211, A117.
  11. ^ "SU Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-01-04.
  12. ^ Müller, G.; Kempf, P. (March 1898), "Zwei neue Veränderliche von kurzer Periode", Astronomische Nachrichten (in German), 146 (3): 37, Bibcode:1898AN....146...37M, doi:10.1002/asna.18981460303. Note: listed as BD. +28°3460.
  13. ^ Luizet, Michel (May 1899), "Sur les deux nouvelles étoiles variables U Petit Renard et SU Cygne", Astronomische Nachrichten (in French), 149 (18): 313, Bibcode:1899AN....149..313L, doi:10.1002/asna.18991491804.
  14. ^ 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, S2CID 119576552.
  15. ^ Shapley, H. (1916), "The variations in spectral type of twenty Cepheid variables", Astrophysical Journal, 44: 273, Bibcode:1916ApJ....44..273S, doi:10.1086/142295.
  16. ^ 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.
  17. ^ 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.
  18. ^ 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

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