Eta Cygni

Eta Cygni (η Cygni) is a star in the northern constellation of Cygnus. It is visible to the naked eye with an apparent visual magnitude of 3.889.[2] The star lies along the main body of the constellation, about midway between Gamma Cygni and Albireo.[8] Based upon an annual parallax shift of 24.17 mas,[1] it is located 135 light years from the Sun.

η Cygni
Location of η Cygni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 19h 56m 18.37222s[1]
Declination +35° 05′ 00.3228″[1]
Apparent magnitude (V) 3.889[2]
Characteristics
Spectral type K0 III[3]
U−B color index +0.881[2]
B−V color index +1.035[2]
Astrometry
Radial velocity (Rv)−25.87±0.14[4] km/s
Proper motion (μ) RA: −33.61[1] mas/yr
Dec.: −27.87[1] mas/yr
Parallax (π)24.17 ± 0.15[1] mas
Distance134.9 ± 0.8 ly
(41.4 ± 0.3 pc)
Absolute magnitude (MV)0.74[5]
Details[4]
Mass1.59[6] M☉
Radius11 R☉
Luminosity52.5 L☉
Surface gravity (log g)2.7 cgs
Temperature4,783±20[6] K
Metallicity [Fe/H]−0.09 dex
Rotational velocity (v sin i)2.2 km/s
Age3.29[6] Gyr
Other designations
η Cyg, 21 Cygni, BD+34° 3798, FK5 1521, HD 188947, HIP 98110, HR 7615, SAO 69116.[7]
Database references
SIMBADdata

At an age of about 3.3[6] billion years, this is an evolved red clump[9] giant star with a stellar classification of K0 III.[3] It is presently on the horizontal branch and is generating energy through the nuclear fusion of helium at its core. The star has about 1.59[6] times the mass of the Sun and has expanded to 11[4] It radiates 52.5 times the solar luminosity from its outer atmosphere at an effective temperature of 4,783 K.[6]

Eta Cygni has five visual companions,[10] of which only component B appears to be physically associated. This magnitude 12.0 star lies at an angular separation of 7.80 arc seconds along a position angle of 206°, as of 2007.[11]

References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
  2. Oja, T. (August 1986), "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series, 65 (2): 405–409, Bibcode:1986A&AS...65..405O.
  3. Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics, 11: 29–50, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333.
  4. Massarotti, Alessandro; et al. (January 2008), "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity", The Astronomical Journal, 135 (1): 209–231, Bibcode:2008AJ....135..209M, doi:10.1088/0004-6256/135/1/209.
  5. Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", Astronomy and Astrophysics, 430: 303–311, arXiv:astro-ph/0409683, Bibcode:2005A&A...430..303C, doi:10.1051/0004-6361:20041440, S2CID 12136256.
  6. Luck, R. Earle (September 2015), "Abundances in the Local Region. I. G and K Giants", The Astronomical Journal, 150 (3): 23, arXiv:1507.01466, Bibcode:2015AJ....150...88L, doi:10.1088/0004-6256/150/3/88, S2CID 118505114, 88.
  7. "eta Cyg". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-02-19.
  8. Marett-Crosby, Michael (2013), Twenty-Five Astronomical Observations That Changed the World: And How To Make Them Yourself, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 231, ISBN 978-1461468004.
  9. Puzeras, E.; et al. (October 2010), "High-resolution spectroscopic study of red clump stars in the Galaxy: iron-group elements", Monthly Notices of the Royal Astronomical Society, 408 (2): 1225–1232, arXiv:1006.3857, Bibcode:2010MNRAS.408.1225P, doi:10.1111/j.1365-2966.2010.17195.x, S2CID 44228180.
  10. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
  11. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
  • Kaler, James B. (September 7, 2012), "Eta Cygni", Stars, University of Illinois, retrieved 2017-02-19.
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