Surface temperature 3,500 K Luminosity 27,000 L☉ | Mass 4.972 × 10^31 kg (25 M☉) Magnitude 10.77 | |
Radius 988.3 million km (1,420 R☉) Similar V354 Cephei, WOH G64, KW Sagittarii, Mu Cephei, VV Cephei | ||
Ky cygni
KY Cygni is a red supergiant of spectral class M3.5Ia located in the constellation Cygnus. It is one of the largest stars known, Its value is very poorly known, Its estimated size is 1,420 R☉ (990,000,000 km; 6.6 au) or (up to 2,850 R☉ (1.98×109 km; 13.3 au) by some estimates). If It is placed at the center of the Solar System, it would extend past the orbit of Jupiter (or Saturn). And it's also one of the most luminous, with about 300,000 or more times the Sun's luminosity. It is approximately 5,000 light-years away.
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Observations
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. It was identified as a variable star in 1930, and later named as KY Cygni. The spectrum was given the MK classification of M3 Ia, with only minor adjustments since.
KY Cygni is heavily reddened due to interstellar extinction, losing an estimate 7.75 magnitudes at visual wavelengths. It would be a naked eye star If no light was lost.
Properties
KY Cygni is a large luminous cool supergiant with a strong stellar wind. It is losing mass at one of the highest rates known for a red supergiant and has been described as a cool hypergiant.
The properties are uncertain, but the temperature is around 3,500 K and the luminosity over 100,000 L☉. A model fit based on K-band infrared brightness gives a luminosity of 273,000 L☉. One based on visual brightness gives an unexpectedly large luminosity of 1,100,000 L☉, with the difference due mainly to the assumptions about the level of extinction. The radius corresponding to the higher luminosity would be over 2,800 R☉, it is somewhat on par with the largest stars known. More recently, integration of the spectral energy distributions across a full range of wavelengths from U band to the 60 micron microwave flux gives a luminosity of 138,000 L☉. The radius corresponding to the lower luminosity would be less than 1,000 R☉.
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. The photographic magnitude range is given as 13.5 - 15.5, while a visual range is 10.60 - 11.74.