WASP-18
Star in the constellation Phoenix
From Wikipedia, the free encyclopedia
WASP-18 is a magnitude 9 star located 400 light-years (120 parsecs) away[2] in the Phoenix constellation of the Southern Hemisphere.[1] It has a mass of 1.29 solar masses.[6]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Phoenix[1] |
| Right ascension | 01h 37m 25.03328s[2] |
| Declination | −45° 40′ 40.3747″[2] |
| Apparent magnitude (V) | 9.273[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| 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 |
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]
| 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 |