KY Cygni is a red supergiant of spectral class M3.5Ia located in the constellation Cygnus. It is approximately 5,000 light-years away.
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Cygnus |
Right ascension | 20h 25m 58.04s[1] |
Declination | +38° 21′ 07.7″[1] |
Apparent magnitude (V) | 11.14[2] (10.60 - 11.74[3]) |
Characteristics | |
Spectral type | M3 Ia[4] (M3.5 Ia[5]) |
U−B color index | +2.91[2] |
B−V color index | +3.39[2] |
Variable type | Lc[5] |
Astrometry | |
Proper motion (μ) | RA: –3.556[1] mas/yr Dec.: –6.061[1] mas/yr |
Parallax (π) | 0.6687 ± 0.0517 mas[1] |
Distance | 4,900 ± 400 ly (1,500 ± 100 pc) |
Absolute magnitude (MV) | –8.18[6] |
Details | |
Radius | 1,033[7] – 1,420[6] R☉ |
Luminosity | 138,000[2] – 270,000[6][8] L☉ |
Surface gravity (log g) | −0.5 (−0.9?)[6] cgs |
Temperature | 3,550[9] K |
Other designations | |
Database references | |
SIMBAD | data |
KY Cyg lies near the bright open cluster NGC 6913, but is not thought to be a member. The location is close to the bright star γ Cygni.[10] It was identified as a variable star in 1930,[11] and later named as KY Cygni.[12] The spectrum was given the MK classification of M3 Ia, with only minor adjustments since.[4]
KY Cygni is heavily reddened due to interstellar extinction, losing an estimated 7.75 magnitudes at visual wavelengths. It would be a naked eye star if no light was lost.[6]
KY Cygni is classified as a luminous red supergiant with a strong stellar wind. It is losing mass at around 4.9×10−6 M☉ and has been described as a cool hypergiant.[2][13]
Its properties are uncertain, but the temperature is around 3,500 K. A model fit based on K-band infrared brightness gives a luminosity of 273,000 L☉, corresponding to a radius of 1,420 R☉. Another model based on visual brightness gives an unexpectedly large luminosity of 1,107,000 L☉, with the difference due mainly to the assumptions about the level of extinction. The radius corresponding to the higher luminosity would be 2,850 R☉. These parameters are larger and more luminous than expected for any red supergiant, making them doubtful.[6] More recently, integration of the spectral energy distributions across a full range of wavelengths from U band to the 60 micron microwave flux gives an even lower luminosity of 138,000 L☉,[2] and calculation of the bolometric luminosity based on its Gaia Data Release 2 parallax gives a luminosity below 70,000 L☉ with a corresponding radius of 672 R☉.[9]
KY Cygni is a variable star with a large amplitude but no clear periodicity. At times, it varies rapidly, at others it is fairly constant for long periods.[10] The photographic magnitude range is given as 13.5 - 15.5,[5] while a visual range is 10.60 - 11.74.[3]