The star, although similar to the Sun in terms of overall contents of heavy elements, is depleted in carbon. The carbon to oxygen molar ratio of 0.23±0.05 for WASP-18 is well below the solar ratio of 0.55.[9]
There is a
red dwarf companion star at a separation of 3,519
AU.[5]
Planetary system
In 2009, the
SuperWASP project announced the discovery of a large,
hot Jupiter type
exoplanet,
WASP-18b, orbiting very close to this star. It has an
orbital period of less than a day and a mass 10 times that of Jupiter.[4]
Observations from the
Chandra X-ray Observatory failed to find any
X-rays coming from WASP-18,[10] and it is thought that this is caused by WASP-18b disrupting the star's
magnetic field by causing a reduction in
convection in the
star's atmosphere. Tidal forces from the planet may also explain the higher amounts of
lithium measured in earlier optical studies of WASP-18.[11]
A 2019 study proposed a second candidate planet with a 2-day orbital period based on
transit-timing variations,[12] but a 2020 study using data from both
TESS 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.[6]
^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