Astronomy:KY Cygni

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Short description: Star in the constellation Cygnus
KY Cygni
Location of KY Cygni in the Sadr region (circled, east is up)
Observation data
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]
Spectral type M3 Ia[4] (M3.5 Ia[5])
U−B color index +2.91[6]
B−V color index +3.39[6]
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[1] mas
Distance4,680+350
−390 ly
(1,436+106
−119 pc)
Details[7]
Mass19 M☉
Radius1,032[lower-alpha 1] R☉
Luminosity150,000 L☉
Surface gravity (log g)−0.5[3] cgs
Temperature3,535 K
Age>9[lower-alpha 2] Myr
Other designations
KY Cyg, GSC 03152-01140, IRAS 20241+3811, IRC+40415, TYC 3152-1140-1, RAFGL 2575, UCAC2 45230193, 2MASS J20255805+3821076
Database references
SIMBADdata

KY Cygni is a variable red supergiant of spectral class M3Ia located in the constellation Cygnus. It is approximately 4,700 light-years away.

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.[8] It was identified as a variable star in 1930,[9] and later named as KY Cygni.[10] 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.[3]

Properties

Size comparison of Betelgeuse, Mu Cephei, KY Cygni, and V354 Cephei, according to estimates derived in 2005[3]

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.[6][11]

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.[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☉,[6] and a 2020 paper published a luminosity of 150,000 L☉, which give a smaller radius of 1,032 R☉ using an effective temperature of 3,535 K.[7]

A visual band light curve for KY Cygni, plotted from data published by Kochanek et al. (2017)[12]

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.[8] The photographic magnitude range is given as 13.5 - 15.5,[5] while a visual range is 10.60 - 11.74.[2]

See also

Notes

  1. ↑ Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
    (5,7723,535)4⋅105.176=1,032.46 R⊙.
  2. ↑ This is only the age at which the star enters the red supergiant phase.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 Alfonso-Garzón, J.; Domingo, A.; Mas-Hesse, J. M.; Giménez, A. (2012). "The first INTEGRAL-OMC catalogue of optically variable sources". Astronomy & Astrophysics 548: A79. doi:10.1051/0004-6361/201220095. Bibcode: 2012A&A...548A..79A. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Cite error: Invalid <ref> tag; no text was provided for refs named levesque
  4. ↑ 4.0 4.1 White, N. M.; Wing, R. F. (1978). "Photoelectric two-dimensional spectral classification of M supergiants". Astrophysical Journal 222: 209. doi:10.1086/156136. Bibcode: 1978ApJ...222..209W. 
  5. ↑ 5.0 5.1 5.2 KY Cyg, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars , Sternberg Astronomical Institute, Moscow, Russia. Accessed on line November 12, 2010.
  6. ↑ 6.0 6.1 6.2 6.3 Mauron, N.; Josselin, E. (2011). "The mass-loss rates of red supergiants and the de Jager prescription". Astronomy and Astrophysics 526: A156. doi:10.1051/0004-6361/201013993. Bibcode: 2011A&A...526A.156M. 
  7. ↑ 7.0 7.1 Comerón, F.; Djupvik, A. A.; Schneider, N.; Pasquali, A. (October 2020). "The historical record of massive star formation in Cygnus". Astronomy & Astrophysics 644: A62. doi:10.1051/0004-6361/202039188. Bibcode: 2020A&A...644A..62C. 
  8. ↑ 8.0 8.1 Romano, 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. 
  9. ↑ Hoffmeister, Cuno (1930). "Relative Koordinaten, Oerter und Karten neuer Veraenderlicher". Mitteilungen der Sternwarte zu Sonneberg 17: 1. Bibcode: 1930MiSon..17....1H. 
  10. ↑ 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. 
  11. ↑ Stickland, D. J. (1985). "IRAS observations of the cool galactic hypergiants". The Observatory 105: 229. Bibcode: 1985Obs...105..229S. 
  12. ↑ Kochanek, C. S.; Shappee, B. J.; Stanek, K. Z.; Holoien, T. W. S.; Thompson, Todd A.; Prieto, J. L.; Dong, Subo; Shields, J. V. et al. (October 2017). "The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0". Publications of the Astronomical Society of the Pacific 129 (980): 104502. doi:10.1088/1538-3873/aa80d9. Bibcode: 2017PASP..129j4502K. 
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