KY Cyg lies near the bright
open clusterNGC 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]
Properties
KY Cygni is classified as a luminous red supergiant with a strong
stellar wind. It is losing mass at around 4.9×10−6M☉ 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]
^
abRomano, G. (1969). "Researches with the Schmidt telescopes. III. Variable stars in the field of gamma Cygni". Memorie della Società Astronomia Italiana. 40: 375.
Bibcode:
1969MmSAI..40..375R.
^Hoffmeister, Cuno (1930). "Relative Koordinaten, Oerter und Karten neuer Veraenderlicher". Mitteilungen der Sternwarte zu Sonneberg. 17: 1.
Bibcode:
1930MiSon..17....1H.
^Ahnert, P.; Van Schewick, H.; Hoffmeister, C. (1941). "Die Veraenderlichen Sterne der noerdlichen Milchstrasse. Teil II". Kleine Veroeffentlichungen der Universitaetssternwarte zu Berlin Babelsberg. 6: 4.1.
Bibcode:
1941KVeBB...6....4A.
^Stickland, D. J. (1985). "IRAS observations of the cool galactic hypergiants". The Observatory. 105: 229.
Bibcode:
1985Obs...105..229S.