WASP-178

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WASP-178 / KELT-26
Location of WASP-178 (circled)
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, possibly Delta Scuti variable[3]
Distance
1,350 ± 10 ly
(412 ± 4 pc)
Details
Myr
TYC 7829-2324-1, GSC 07829-02324, 2MASS J15090488-4242178, KELT-26[1]
Database references
SIMBADdata

WASP-178, also known as KELT-26 and HD 134004, is a

ultra-hot Jupiter planet, WASP-178b
, making it one of the hottest stars known to host a hot Jupiter.

Physical properties

WASP-178 has a

MASCARA-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 is 430+310
−250 million years old.[3] For comparison, Sirius A has a mass of 2.063 M☉,[5] a radius of 1.711 R☉,[6] an effective temperature of 9,940 K,[7] a luminosity of 25.4 L☉,[6] and an age of 242 Myr.[5]

Much like Sirius A, the star is a likely Am star and a slow 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 in chromium, nickel, yttrium, and barium, while being slightly poor in calcium and scandium.[2]

Variability

Aside from periodic dimming caused by the transiting planet, the star experiences regular oscillations in brightness by a few thousandths of a magnitude. 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 the instability strip in the Hertzsprung–Russell diagram implies that WASP-178 may be a Delta Scuti variable.[3]

Possible stellar companion

Significant excess noise in the

milliarcseconds in 254 astrometric measurements, is reported for WASP-178 in the Gaia DR2 catalogue. This may suggest a previously unresolved and invisible binary companion.[2]

Planetary system

Main article: WASP-178b

In 2019, two teams, part of the

ultra-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 of 1.81±0.09 RJ[2] or 1.940+0.060
−0.058 RJ,[3] placing it among the largest planets
discovered so far.

silicate 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 by ionized magnesium and iron.[14]

The WASP-178 planetary system[2]
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

References

  1. ^ a b c d e f g h "HD 134004". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-08.
  2. ^
    ISSN 0035-8711
    .
  3. ^
    ISSN 0004-6256
    .
  4. ISSN 0004-6256
    .
  5. ^
    S2CID 51839102
    .
  6. ^
    S2CID 8792889
    .
  7. doi:10.1017/S1743921304004314
    .
  8. ISSN 0004-6361
    .
  9. ISSN 2041-8205
    .
  10. doi:10.1051/0004-6361/202450064
    .
  11. ^
    ISSN 0004-6361
    .
  12. ^ a b c NASA Hubble Mission Team (2022-04-06). "Hubble Probes Extreme Weather on Ultra-Hot Jupiters". Goddard Space Flight Center. Retrieved 2024-08-14.
  13. PMID 35388193
    .
  14. ISSN 0004-6361
    .
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