WASP-178, also known as KELT-26 and HD 134004, is a star located about 1,350 light-years (410 parsecs) away in the southern constellation of Lupus. It is a hot A-type main sequence star or subgiant, a likely Am star, and a possible Delta Scuti variable, about twice as massive as the Sun and twenty times as luminous. In late 2019, the star was discovered to be orbited by an ultra-hot Jupiter planet, WASP-178b, making it one of the hottest stars known to host a hot Jupiter.
  | |
| Observation data Epoch J2000.0[1] Equinox J2000.0[1] | |
|---|---|
| Constellation | Lupus |
| Right ascension | 15h 09m 04.893358118400s[1] |
| Declination | −42° 42′ 17.789374620″[1] |
| Apparent magnitude (V) | 9.95[1] |
| Characteristics | |
| Spectral type | A1IV-V[2] |
| Variable type | Planetary transit variable, possibly Delta 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 | |
| Database references | |
| SIMBAD | data |
Physical properties
editWASP-178 has a spectral type of A1IV-V, indicating that it is in an evolutionary stage between a main sequence star and a subgiant. The star is comparable to Sirius A in mass and radius, but slightly cooler, older, and less luminous. It is about twice as massive as the Sun and has a radius of 1.67[2] or 1.80[3] R☉, with an effective temperature of roughly 9,000 K. A 2019 estimate of 9360±150 K makes WASP-178 the second-hottest host to a hot Jupiter ever discovered, behind KELT-9 (10,170 K) and ahead of 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
editAside 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
editSignificant excess noise in the astrometry, totaling to 0.18 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
editIn 2019, two teams, part of the WASP and KELT planet surveys respectively, independently reported the discovery of an exoplanet orbiting the star using the transit method.[2][3] The planet was revealed to be an 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.
Photometric observations at the CHEOPS space telescope revealed that the planet has a low geometric 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 vaporize 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]
| 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
edit- ^ a b c d e f g h "HD 134004". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-08.
- ^ a b c d e f g h i j k l m n o p q r Hellier, Coel; et al. (2019-11-21). "WASP-South hot Jupiters: WASP-178b, WASP-184b, WASP-185b, and WASP-192b". Monthly Notices of the Royal Astronomical Society. 490 (1): 1479–1487. arXiv:1907.11667. doi:10.1093/mnras/stz2713. ISSN 0035-8711.
- ^ a b c d e f g h i j k l Martínez, Romy Rodríguez; et al. (2020-09-01). "KELT-25 b and KELT-26 b: A Hot Jupiter and a Substellar Companion Transiting Young A Stars Observed by TESS*". The Astronomical Journal. 160 (3): 111. arXiv:1912.01017. Bibcode:2020AJ....160..111R. doi:10.3847/1538-3881/ab9f2d. ISSN 0004-6256.
- ^ Stassun, Keivan G.; et al. (2019-10-01). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. ISSN 0004-6256.
- ^ a b Bond, Howard E.; Schaefer, Gail H.; Gilliland, Ronald L.; Holberg, Jay B.; Mason, Brian D.; Lindenblad, Irving W.; et al. (2017). "The Sirius system and its astrophysical puzzles: Hubble Space Telescope and ground-based astrometry". The Astrophysical Journal. 840 (2): 70. arXiv:1703.10625. Bibcode:2017ApJ...840...70B. doi:10.3847/1538-4357/aa6af8. S2CID 51839102.
- ^ a b Liebert, James; Young, P. A.; Arnett, David; Holberg, J. B.; Williams, Kurtis A. (2005). "The Age and Progenitor Mass of Sirius B". The Astrophysical Journal. 630 (1): L69–L72. arXiv:astro-ph/0507523. Bibcode:2005ApJ...630L..69L. doi:10.1086/462419. S2CID 8792889.
- ^ Adelman, Saul J. (8–13 July 2004). "The Physical Properties of normal A stars". Proceedings of the International Astronomical Union. Vol. 2004. Poprad, Slovakia: Cambridge University Press. pp. 1–11. Bibcode:2004IAUS..224....1A. doi:10.1017/S1743921304004314.
- ^ Royer, F.; et al. (2002). "Rotational velocities of A-type stars: I. Measurement of v sin i in the southern hemisphere". Astronomy & Astrophysics. 381 (1): 105–121. arXiv:astro-ph/0110490. Bibcode:2002A&A...381..105R. doi:10.1051/0004-6361:20011422. ISSN 0004-6361.
- ^ Yang, Wuming; et al. (2013-02-22). "Evolution of Rotational Velocities of A-Type Stars". The Astrophysical Journal. 765 (2): L36. arXiv:1302.0448. Bibcode:2013ApJ...765L..36Y. doi:10.1088/2041-8205/765/2/L36. ISSN 2041-8205.
- ^ Cont, D.; et al. (2024). "Exploring the ultra-hot Jupiter WASP-178b. Constraints on atmospheric chemistry and dynamics from a joint retrieval of VLT/CRIRES+ and space photometric data". Astronomy & Astrophysics. arXiv:2406.08166. doi:10.1051/0004-6361/202450064.
- ^ a b Pagano, I.; et al. (2024). "Constraining the reflective properties of WASP-178 b using CHEOPS photometry". Astronomy & Astrophysics. 682: A102. arXiv:2309.09037. Bibcode:2024A&A...682A.102P. doi:10.1051/0004-6361/202346705. ISSN 0004-6361.
- ^ 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.
- ^ Lothringer, Joshua D.; Sing, David K.; Rustamkulov, Zafar; Wakeford, Hannah R.; Stevenson, Kevin B.; Nikolov, Nikolay; Lavvas, Panayotis; Spake, Jessica J.; Winch, Autumn T. (2022-04-07). "UV absorption by silicate cloud precursors in ultra-hot Jupiter WASP-178b". Nature. 604 (7904): 49–52. arXiv:2204.03639. Bibcode:2022Natur.604...49L. doi:10.1038/s41586-022-04453-2. ISSN 0028-0836. PMID 35388193.
- ^ Damasceno, Y. C.; et al. (2024). "The atmospheric composition of the ultra-hot Jupiter WASP-178 b observed with ESPRESSO". Astronomy & Astrophysics. 689. EDP Sciences: A54. arXiv:2406.08348. Bibcode:2024A&A...689A..54D. doi:10.1051/0004-6361/202450119. ISSN 0004-6361.