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WASP-18
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<h2 id="planetary-system">Planetary system</h2> <p>In 2009, the <a href="/facts/SuperWASP/fp58Y205">SuperWASP</a> project announced the discovery of a large, <a href="/facts/Hot_Jupiter/9wSFCuxk">hot Jupiter</a> type <a href="/facts/Exoplanet/zjfmqfUf">exoplanet</a>, <a href="/facts/WASP-18b/7FLTw4YN">WASP-18b</a>, orbiting very close to this star. It has an <a href="/facts/Orbital_period/94f56uh2">orbital period</a> of less than a day and a mass 10 times that of Jupiter.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>Observations from the <a href="/facts/Chandra_X-ray_Observatory/zU89xG3a">Chandra X-ray Observatory</a> failed to find any <a href="/facts/X-ray/wseP79cN">X-rays</a> coming from WASP-18,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> and it is thought that this is caused by WASP-18b disrupting the star's <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a> by causing a reduction in <a href="/facts/Convection/E8vsCPhu">convection</a> in the <a href="/facts/Stellar_atmosphere/Ll4LjxIn">star's atmosphere</a>. Tidal forces from the planet may also explain the higher amounts of <a href="/facts/Lithium/7vXX6BWA">lithium</a> measured in earlier optical studies of WASP-18.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>A 2019 study proposed a second candidate planet with a 2-day orbital period based on <a href="/facts/Transit-timing_variation/yqK6GSYW">transit-timing variations</a>,<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> but a 2020 study using data from both <a href="/facts/Transiting_Exoplanet_Survey_Satellite/IxEjYsYd">TESS</a> and ground-based surveys ruled out the existence of a planet with the proposed properties, setting an upper limit of 10 Earth masses on any planet with this period.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> The WASP-18 planetary system<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a><table><tbody><tr><th>Companion(in order from star)</th><th><a href="/facts/Mass/HHdc8XmF">Mass</a></th><th><a href="/facts/Semi-major_and_semi-minor_axes/l7JES2wo">Semimajor axis</a>(<a href="/facts/Astronomical_unit/gjsbu5xU">AU</a>)</th><th><a href="/facts/Orbital_period/94f56uh2">Orbital period</a>(<a href="/facts/Day/MTAtWLDj">days</a>)</th><th><a href="/facts/Orbital_eccentricity/WGlB4NBn">Eccentricity</a></th><th><a href="/facts/Orbital_inclination/TQCFWyfd">Inclination</a></th><th><a href="/facts/Radius/9Gr9deYD">Radius</a></th></tr><tr><td><a href="/facts/WASP-18b/7FLTw4YN">b</a></td><td>10.20±0.35 <a href="/facts/Jupiter_mass/EtLUmeEN">MJ</a></td><td>0.02024+0.00029−0.00031</td><td>0.94145223(24)</td><td>0.0051+0.0070−0.0037</td><td>83.5+2.0−1.6<a href="/facts/Degree_(angle)/f48Ns8SX">°</a></td><td>1.240±0.079 <a href="/facts/Jupiter_radius/sT995rQ5">RJ</a></td></tr></tbody></table> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/SuperWASP/fp58Y205">SuperWASP</a></li> <li><a href="/facts/List_of_exoplanets/op9vhHys">List of exoplanets</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"WASP-18b". Exoplanet Transit Database. Retrieved 2009-08-29. <a href="http://var2.astro.cz/ETD/etd.php?STARNAME=WASP-18&PLANET=b" target="_blank">http://var2.astro.cz/ETD/etd.php?STARNAME=WASP-18&PLANET=b</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Cortés-Zuleta, Pía; Rojo, Patricio; et al. (April 2020). "TraMoS. V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab". Astronomy & Astrophysics. 636: A98. arXiv:2001.11112. Bibcode:2020A&A...636A..98C. doi:10.1051/0004-6361/201936279. S2CID 241596186. <a href="/wiki/Astronomy_%26_Astrophysics" target="_blank">/wiki/Astronomy_%26_Astrophysics</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Polanski, Alex S.; Crossfield, Ian J. M.; Howard, Andrew W.; Isaacson, Howard; Rice, Malena (2022), "Chemical Abundances for 25 JWST Exoplanet Host Stars with KeckSpec", Research Notes of the American Astronomical Society, 6 (8): 155, arXiv:2207.13662, Bibcode:2022RNAAS...6..155P, doi:10.3847/2515-5172/ac8676 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Csizmadia, Sz.; Hellard, H.; Smith, A. M. S. (March 2019). "An estimate of the k2 Love number of WASP-18Ab from its radial velocity measurements". Astronomy & Astrophysics. 623: A45. arXiv:1812.04463. Bibcode:2019A&A...623A..45C. doi:10.1051/0004-6361/201834376. S2CID 119387925. <a href="/wiki/Astronomy_%26_Astrophysics" target="_blank">/wiki/Astronomy_%26_Astrophysics</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Hellier, Coel; et al. (2009). "An orbital period of 0.94days for the hot-Jupiter planet WASP-18b" (PDF). Nature. 460 (7259): 1098–1100. Bibcode:2009Natur.460.1098H. doi:10.1038/nature08245. hdl:2268/28276. PMID 19713926. S2CID 205217669. <a href="http://orbi.ulg.ac.be/bitstream/2268/28276/1/nature08245.pdf" target="_blank">http://orbi.ulg.ac.be/bitstream/2268/28276/1/nature08245.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Pillitteri, I.; et al. (July 2014). "No X-rays from WASP-18. Implications for its age, activity, and the influence of its massive hot Jupiter". Astronomy & Astrophysics. 567: A128. arXiv:1406.2620. Bibcode:2014A&A...567A.128P. doi:10.1051/0004-6361/201423579. S2CID 118527777. <a href="https://www.aanda.org/articles/aa/abs/2014/07/aa23579-14/aa23579-14.html" target="_blank">https://www.aanda.org/articles/aa/abs/2014/07/aa23579-14/aa23579-14.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"NASA's Chandra X-ray Observatory Finds Planet That Makes Star Act Deceptively Old". Chandra X-ray Observatory. Retrieved 20 September 2014. <a href="http://chandra.harvard.edu/press/14_releases/press_091614.html" target="_blank">http://chandra.harvard.edu/press/14_releases/press_091614.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Pearson, Kyle A. (December 2019). "A Search for Multiplanet Systems with TESS Using a Bayesian N-body Retrieval and Machine Learning". The Astronomical Journal. 158 (6): 243. arXiv:1907.03377. Bibcode:2019AJ....158..243P. doi:10.3847/1538-3881/ab4e1c. S2CID 195833716. <a href="https://doi.org/10.3847%2F1538-3881%2Fab4e1c" target="_blank">https://doi.org/10.3847%2F1538-3881%2Fab4e1c</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Cortés-Zuleta, Pía; Rojo, Patricio; et al. (April 2020). "TraMoS. V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab". Astronomy & Astrophysics. 636: A98. arXiv:2001.11112. Bibcode:2020A&A...636A..98C. doi:10.1051/0004-6361/201936279. S2CID 241596186. <a href="/wiki/Astronomy_%26_Astrophysics" target="_blank">/wiki/Astronomy_%26_Astrophysics</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Cortés-Zuleta, Pía; Rojo, Patricio; et al. (April 2020). "TraMoS. V. Updated ephemeris and multi-epoch monitoring of the hot Jupiters WASP-18Ab, WASP-19b, and WASP-77Ab". Astronomy & Astrophysics. 636: A98. arXiv:2001.11112. Bibcode:2020A&A...636A..98C. doi:10.1051/0004-6361/201936279. S2CID 241596186. <a href="/wiki/Astronomy_%26_Astrophysics" target="_blank">/wiki/Astronomy_%26_Astrophysics</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> </ol>