WASP-18

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 (Rv)	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 MJ	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 RJ

See also

• SuperWASP
• List of exoplanets

References

1. "WASP-18b". Exoplanet Transit Database. Retrieved 2009-08-29.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. "WASP-18". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 5 November 2023.
9. 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
10. 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.
11. "NASA's Chandra X-ray Observatory Finds Planet That Makes Star Act Deceptively Old". Chandra X-ray Observatory. Retrieved 20 September 2014.
12. 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.