Astronomy:Kepler-18

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Kepler-18 is a star with a system of three exoplanets, positioned in the northern Constellation of Cygnus. It has an apparent visual magnitude of 14.0,[1] requiring a telescope to view. Based on parallax measurements, it is located at a distance of approximately 1,430 light-years (440 pc). It is drifting closer with a line of sight velocity component of −18.4 km/s.[2]

This is an older star with an estimated age of around ten billion years. It has similar properties to the Sun with almost the same mass and a 10% larger radius. The star is radiating 93% of the Sun's luminosity from its photosphere at an effective temperature of 5,383 K.[3]

Planetary system

The star is orbited by 3 confirmed transiting planets, announced in 2011.[3] In 2021, it was found the orbital plane of Kepler-18d is slowly changing, likely under the gravitational influence of the additional giant planet.[4]

The Kepler-18 planetary system[3][5]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b 6.9 ± 3.4 M⊕ 0.0447 ± 0.0006 3.504725 ± 0.000028 — 84.92 ± 0.26° 2.00 ± 0.10 R⊕
c 17.3 ± 1.9 M⊕ 0.0752 ± 0.0011 7.6415716 — 87.68 ± 0.22° 5.49 ± 0.26 R⊕
d 16.4 ± 1.4 M⊕ 0.1172 ± 0.0017 14.858941 — 88.07 ± 0.1° 6.98 ± 0.33 R⊕

References

  1. ↑ Zacharias, N. (2012). The fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). VizieR On-line Data Catalog. 1322. Bibcode: 2012yCat.1322....0Z. 
  2. ↑ Jönsson, Henrik et al. (August 17, 2020). "APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South". The Astronomical Journal (American Astronomical Society) 160 (3): 120. doi:10.3847/1538-3881/aba592. ISSN 0004-6256. Bibcode: 2020AJ....160..120J. 
  3. ↑ 3.0 3.1 3.2 Cochran, William D. et al. (2011). "Kepler 18-b, c, and d: A System Of Three Planets Confirmed by Transit Timing Variations, Lightcurve Validation, Spitzer Photometry and Radial Velocity Measurements". The Astrophysical Journal Supplement Series 197 (1): 7. doi:10.1088/0067-0049/197/1/7. Bibcode: 2011ApJS..197....7C. 
  4. ↑ Shahaf, Sahar; Mazeh, Tsevi; Zucker, Shay; Fabrycky, Daniel (2021), "Systematic search for long-term transit duration changes in Kepler transiting planets", Monthly Notices of the Royal Astronomical Society 505 (1): 1293–1310, doi:10.1093/mnras/stab1359, Bibcode: 2021MNRAS.505.1293S 
  5. ↑ Montet, Benjamin T.; Johnson, John Asher (2013), "Model-Independent Stellar and Planetary Masses from Multi-Transiting Exoplanetary Systems", The Astrophysical Journal 762 (2): 112, doi:10.1088/0004-637X/762/2/112, Bibcode: 2013ApJ...762..112M 

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Coordinates: Sky map 19h 63m 19.06s, +46° 44′ 47.94″



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