R Cygni

R Cygni is a variable star of the Mira type in the constellation Cygnus, less than 4' from θ Cygni. This is a red giant star on the asymptotic giant branch located around 2,200 light years away. It is an S-type star ranging between spectral types S2.5,9e to S6,9e(Tc).^[4]

R Cygni

Observation data Epoch J2000      Equinox J2000
Constellation	Cygnus
Right ascension	19h 36m 49.35633s[1]
Declination	+50° 11′ 59.7198″[1]
Apparent magnitude (V)	6.1 - 14.4[2]
Characteristics
Evolutionary stage	AGB[3]
Spectral type	S2.5,9e-S6,9e(Tc)[4]
Variable type	Mira[2]
Astrometry
Proper motion (μ)	RA: −3.158[1] mas/yr Dec.: −5.755[1] mas/yr
Parallax (π)	1.4835±0.0963 mas[1]
Distance	2,200 ± 100 ly (670 ± 40 pc)
Details
Mass	0.85[5] M☉
Luminosity	11,700[6] L☉
Surface gravity (log g)	−0.50[5] cgs
Temperature	2,538[5] K
Metallicity [Fe/H]	+0.50[5] dex
Other designations
R Cyg, AAVSO 1934+49, BD+49 3064, HD 185456, HIP 31822, SAO 31822, WDS J19368+5012[7]
Database references
SIMBAD	data

R Cygni light curve, showing the period-doubling

Stars at this mass range and evolutionary stage are pulsationally unstable, displaying a variation in their light output.^[8] R Cygni has a maximum magnitude of 6.1 and a minimum magnitude of 14.4, with a period of 426.45 days.^[2] The variation of this star was discovered by English astronomer N. R. Pogson in 1852, and it has a history of recorded brightness measurements stretching back more than a century.^[8] R Cygni shows distinct period-doubling, where alternate maxima are of different brightness, hence the real period of pulsation could be considered to be twice that from one maximum to the next.^[8]

The Catalog of Components of Double and Multiple Stars lists 10th magnitude BD+49 3065 as a companion to R Cygni, at a separation of 91", and both stars lie at approximately the same distance. The Washington Double Star Catalog additionally lists a 15th magnitude star as a companion at a separation of about 14".^[9]

See also

• List of largest known stars