SU Cygni

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]

  1. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference GaiaEDR3 was invoked but never defined (see the help page).
  3. ^ a b c Cite error: The named reference Samus_et_al_2017 was invoked but never defined (see the help page).
  4. ^ a b c Cite error: The named reference Evans_et_al_2013 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Eggleton_Yakut_2017 was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Gontcharov_2006 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference Groenewegen_2008 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Imbert_1984 was invoked but never defined (see the help page).
  9. ^ a b Cite error: The named reference Andrievsky_et_al_2013 was invoked but never defined (see the help page).
  10. ^ a b c Cite error: The named reference Kervella_et_al_2019 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Müller_Kempf_1898 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Luizet_1899 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Maddrill_1906 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference Shapley_1916 was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference Madore_1977 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference Evans_et_al_1985 was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Wahlgren_Evans_1998 was invoked but never defined (see the help page).