  | |
| Observation data Epoch J2000.0[1] Equinox J2000.0[1] | |
|---|---|
| Constellation | Lupus |
| Right ascension | 15h 09m 04.89336s[1] |
| Declination | −42° 42′ 17.7894″[1] |
| Apparent magnitude (V) | 9.95[1] |
| Characteristics | |
| Spectral type | A1IV-V[2] |
| Variable type | Planetary transit variable, possiblyDelta Scuti variable[3] |
| Astrometry | |
| Radial velocity (Rv) | −23.908[2] km/s |
| Proper motion (μ) | RA: -10.243[1]mas/yr Dec.: −5.636[1]mas/yr |
| Parallax (π) | 2.4248±0.0216 mas[1] |
| Distance | 1,350 ± 10 ly (412 ± 4 pc) |
| Details | |
| Mass | 2.07±0.11[2] M☉ |
| Radius | 1.67±0.07[2] R☉ |
| Luminosity | 16.2+3.7 −1.8,[3]21.4+1.9 −2.0[4] L☉ |
| Surface gravity (log g) | 4.31±0.04[2] cgs |
| Temperature | 9360±150[2] K |
| Metallicity [Fe/H] | 0.21±0.16[2] dex |
| Rotational velocity (v sin i) | 8.2±0.6[2] km/s |
| Age | 430+310 −250[3] Myr |
| Other designations | |
| CD−42°10057,CPD−42°6923,Gaia DR2 6003809889735481856,HD 134004,PPM 320287,TOI-1337,TIC 160708862,WASP-178,TYC 7829-2324-1,GSC 07829-02324,2MASS J15090488-4242178,KELT-26[1] | |
| Database references | |
| SIMBAD | data |
WASP-178, also known asKELT-26 andHD 134004, is astar located about 1,350 light-years (410 parsecs) away in thesouthernconstellation ofLupus. It is a hotA-type main sequence star orsubgiant, a likelyAm star, and a possibleDelta Scuti variable, about twice as massive as theSun and twenty times as luminous. In late 2019, the star was discovered to be orbited by anultra-hot Jupiter planet,WASP-178b, making it one of the hottest stars known to host a hot Jupiter.
WASP-178 has aspectral type of A1IV-V, indicating that it is in anevolutionary stage between amain sequence star and asubgiant. The star is comparable toSirius A in mass and radius, but slightly cooler, older, and less luminous. It is about twice as massive as theSun and has a radius of 1.67[2] or 1.80[3]R☉, with aneffective temperature of roughly 9,000K. A 2019 estimate of9360±150 K makes WASP-178 the second-hottest host to a hot Jupiter ever discovered, behindKELT-9 (10,170 K) and ahead ofMASCARA-2 (8,980 K),[2] though a lower estimate (8,640+500
−240 K) provided by another paper[3] may put it below MASCARA-2. The star is around 20 times brighter than the Sun and is430+310
−250 million years old.[3] For comparison, Sirius A has a mass of 2.063M☉,[5] a radius of 1.711R☉,[6] an effective temperature of 9,940 K,[7] a luminosity of 25.4L☉,[6] and an age of 242 Myr.[5]
Much like Sirius A, the star is a likelyAm star and aslow rotator, with a rotational velocity of 8.2–12.2 km/s.[2][3] For comparison, Sirius A has a rotational velosity of 16 km/s,[8] while typical A-type stars rotate much faster at around 160 km/s.[9] It has a near-[3] or above-solar[2]metallicity. The star is rich inchromium,nickel,yttrium, andbarium, while being slightly poor incalcium andscandium.[2]
Aside from periodic dimming caused by the transiting planet, the star experiences regular oscillations in brightness by a few thousandths of amagnitude. The period at which the oscillations occur is measured to be 0.185 days, almost exactly one-eighteenth of WASP-178b's orbital period. The planet's mass is likely too small to cause periodic swaying of the host star, therefore it remains to be known whether this is merely coincidental.[3]
The nature of the luminosity fluctuations, namely the period and amplitude, along with the star's position within theinstability strip in theHertzsprung–Russell diagram implies that WASP-178 may be aDelta Scuti variable.[3]
Significant excess noise in theastrometry, totaling to 0.18milliarcseconds in 254 astrometric measurements, is reported for WASP-178 in theGaia DR2 catalogue. This may suggest a previously unresolved and invisiblebinary companion.[2]
In 2019, two teams, part of theWASP andKELTplanet surveys respectively, independently reported the discovery of anexoplanet orbiting the star using thetransit method.[2][3] The planet was revealed to be anultra-hot Jupiter revolving around the star every 3.3 days a mere 0.0558 AU (8,350,000 km) away, heating its surface up to a white-hot 2,470 K (2,200 °C; 3,990 °F).[2] As a result of intense stellar radiation it receives, some of the highest known in an ultra-hot Jupiter,[10] the planet's atmosphere is inflated to a radius of1.81±0.09RJ[2] or1.940+0.060
−0.058RJ,[3] placing it among thelargest planets discovered so far.
Photometric observations at theCHEOPSspace telescope revealed that the planet has a lowgeometric albedo of 0.1–0.35, typical of giant planets.[11] Based on this, the dayside temperature of WASP-178b is estimated at 2,250–2,800 K,[11] more than enough to vaporizesilicate rock.[12] As one side of the planet always faces the star (tidal locking), the atmosphere on the heated daytime side blows across the planet toward the nighttime side in winds reaching upwards of 2,000 miles per hour (3,200 km/h).[12] On the nightside of the planet, minerals that evaporated on the dayside may cool and condense into rock that pours down from clouds as rain.[12]Silicon monoxide in particular was reported to have been discovered on WASP-178b in 2022, the first time the compound was detected in an exoplanet, but consistent with theoretical models on silicate minerals at high temperatures.[13] In 2024, however, a follow-up study found that the atmosphere was instead more likely dominated byionizedmagnesium andiron.[14]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 1.66±0.12 MJ | 0.0558±0.0010 | 3.3448285±0.0000012 | 0 | 85.7±0.6° | 1.81±0.09 RJ |
