WASP-18

Star in the constellation Phoenix

WASP-18
Observation data Epoch J2000.0 Equinox J2000.0
Constellation	Phoenix^[1]
Right ascension	01^h 37^m 25.03328^s^[2]
Declination	−45° 40′ 40.3747″^[2]
Apparent magnitude (V)	9.273^[3]
Characteristics
Spectral type	F6IV/V^[4] + M6.5V^[5]
Astrometry

Radial velocity (R_v)	3.47±0.34^[2] km/s
Proper motion (μ)	RA: 25.404(10) mas/yr^[2] Dec.: 20.479(11) mas/yr^[2]
Parallax (π)	8.1443 ± 0.0116 mas^[2]
Distance	400.5 ± 0.6 ly (122.8 ± 0.2 pc)

Details^[6]

Mass	1.294+0.063 −0.061 `M`_☉
Radius	1.319+0.061 −0.062 `R`_☉
Luminosity	2.68+0.28 −0.26 `L`_☉
Surface gravity (log g)	4.310+0.036 −0.033 cgs
Temperature	6432±48 K
Metallicity [Fe/H]	0.107±0.080 dex
Rotational velocity (v sin i)	11.9±1.2^[7] km/s
Age	1.57+1.4 −0.94 Gyr

Other designations
CD−46 449, CPD−46 168, HD 10069, HIP 7562, SAO 215585, PPM 306061, TOI-185, TIC 100100827, WASP-18, TYC 8040-72-1, 2MASS J01372503-4540404^[8]
Database references
SIMBAD	A
	B
Exoplanet Archive	data

WASP-18 is a magnitude 9 star located 400 light-years (120 parsecs) away in the Phoenix constellation of the southern hemisphere.^[1] It has a mass of 1.29 solar masses.^[6]

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]

The WASP-18 planetary system^[6]
Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	10.20±0.35 M_J	0.02024+0.00029 −0.00031	0.94145223(24)	0.0051+0.0070 −0.0037	83.5+2.0 −1.6°	1.240±0.079 R_J

References

^ ^a ^b "WASP-18b". Exoplanet Transit Database. Retrieved 2009-08-29.
^ ^a ^b ^c ^d ^e Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ Maxted, P. F. L.; et al. (2011). "UBV(RI)C photometry of transiting planet hosting stars". Monthly Notices of the Royal Astronomical Society. 418 (2): 1039–1042. arXiv:1108.0349. Bibcode:2011MNRAS.418.1039M. doi:10.1111/j.1365-2966.2011.19554.x. S2CID 117056033.
^ ^a ^b 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 ^b 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 ^b ^c ^d 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.
^ Torres, Guillermo; et al. (2012). "Improved Spectroscopic Parameters for Transiting Planet Hosts". The Astrophysical Journal. 757 (2). 161. arXiv:1208.1268. Bibcode:2012ApJ...757..161T. doi:10.1088/0004-637X/757/2/161. S2CID 16580774.
^ "WASP-18". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 5 November 2023.
^ 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
^ 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.
^ "NASA's Chandra X-ray Observatory Finds Planet That Makes Star Act Deceptively Old". Chandra X-ray Observatory. Retrieved 20 September 2014.
^ 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.

Constellation of Phoenix

Stars

Bayer	α (Ankaa) β γ δ ε ζ (Wurren) η θ ι κ λ¹ λ² μ ν ξ π ρ σ τ υ φ χ ψ ω
Variable	RV SX YZ AD AE AI AW AZ BB BD
HR	6 23 73 109 111 120 140 148 162 171 198 202 209 229 299 350 408 411 443 447 519 524 537 574 588 632 636 659 686 698 706 8910 8920 8929 8959 8993 9001 9046 9077 9082
HD	2039 5388 6434 (Nenque) 8535 9895 11421 13218 13387 223549 224782
Other	CD-44 170 BPM 30551 HE 0107-5240 NGC 405 WASP-4 WASP-5 WASP-18 WASP-29 WASP-96 WD 2359-434