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HAT-P-18
Star in the constellation Hercules From Wikipedia, the free encyclopedia
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HAT-P-18 is a K-type main-sequence star about 530 light-years away. The star is very old and has a concentration of heavy elements similar to solar abundance.[5] A survey in 2015 detected very strong starspot activity on HAT-P-18.[7]
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Planetary system
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In 2010 a transiting hot Saturn-sized planet was detected.[3] Its equilibrium temperature is 841 K.[8]
In 2014, observations utilizing the Rossiter–McLaughlin effect detected an exoplanet, HAT-P-18b, on a retrograde orbit, with an angle between orbital plane of the planet and the parent star equatorial plane equal to 132±15°.[9]
Transit-timing variation measurements in 2015 did not detect additional planets in the system.[10]
In 2016, the transmission optical spectra of the planet indicated that the atmosphere is lacking detectable clouds or hazes, and is blue in color due to Rayleigh scattering of light.[11] The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years.[12] By contrast, spectra taken in 2022 showed extensive haze and clear evidence of water vapour, along with the tail of escaping helium.[13]
The dayside temperature of HAT-P-18b was measured in 2019 to be 1004+78
−94 K.[14]
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References
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