KY Cygni
Star in the constellation Cygnus
From Wikipedia, the free encyclopedia
KY Cygni is a variable red supergiant or hypergiant of spectral class M3Ia located in the constellation Cygnus. It is approximately 4,700 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) | 10.60 - 11.74[2] |
| Characteristics | |
| Evolutionary stage | Red supergiant[3] or hypergiant[4] |
| Spectral type | M3 Ia[5] (M3.5 Ia[6]) |
| U−B color index | +2.91[7] |
| B−V color index | +3.39[7] |
| Variable type | Lc[6] |
| 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 | 4,680+350 −390 ly (1,436+106 −119 pc)[8] |
| Absolute magnitude (MV) | −8.18[3] |
| Details[9] | |
| Mass | 19 M☉ |
| Radius | 1,032[a] R☉ |
| Luminosity | 150,000 L☉ |
| Surface gravity (log g) | −0.5[3] cgs |
| Temperature | 3,500±100[3] K |
| Age | >9[b] Myr |
| Other designations | |
| RAFGL 2575, UCAC2 45230193, KY Cyg, TYC 3152-1140-1, GSC 03152-01140, IRAS 20241+3811, IRC +40415, 2MASS J20255805+3821076 | |
| Database references | |
| SIMBAD | data |
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.[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.[5]
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.[3]
Properties
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.[7][4]
Its properties are uncertain, but the effective temperature is around 3,500±100 K.[3] A model fit based on K-band infrared brightness gives a luminosity of 273,000+87,000
−66,000 L☉, corresponding to a radius of 1,420±284 R☉.[3] Another model based on visual brightness gives an unexpectedly large luminosity of 1,107,000+352,000
−247,000 L☉, with the difference due mainly to the assumptions about the level of extinction.[3] The radius corresponding to the higher luminosity would be 2,850±570 R☉. These parameters are larger and more luminous than expected for any red supergiant, making them doubtful.[3] 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☉,[7] and a 2020 paper published a luminosity of 150,000 L☉, which give a smaller radius of 1,032 R☉ using a spectral type of M4, which suggests an assumed effective temperature of 3,535 K.[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,[6] while a visual range is 10.60 - 11.74.[2]
See also
Notes
- Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
- .
- This is only the age at which the star enters the red supergiant phase.
