HAT-P-18

Last updated
HAT-P-18
Observation data
Epoch J2000       Equinox J2000
Constellation Hercules [1]
Right ascension 17h 05m 23.1475s [2]
Declination +33° 00′ 44.940″ [2]
Apparent magnitude  (V)12.759 [3]
Characteristics
Spectral type K2V
Astrometry
Radial velocity (Rv)-11.83 km/s
Proper motion (μ)RA: −14.002(9) mas/yr [2]
Dec.: −36.751(11) mas/yr [2]
Parallax (π)6.1863±0.0093  mas [2]
Distance 527.2 ± 0.8  ly
(161.6 ± 0.2  pc)
Details [4]
Mass 0.750+0.015
−0.014  M☉
Radius 0.7202+0.0095
−0.01  R☉
Luminosity 0.27±0.04 [5]   L☉
Surface gravity (log g)4.599±0.013  cgs
Temperature 4835+39
−35  K
Metallicity 0.044+0.060
−0.051
Rotation 14.66±0.03 d [5]
Rotational velocity (v sin i)0.5±0.5 [5]  km/s
Age 12.4+4.4
−6.4 [5]   Gyr
Other designations
Gaia DR2 1334573817793362560, GSC 02594-00646, 2MASS J17052315+3300450 [6]
Database references
SIMBAD data

HAT-P-18 is a K-type main-sequence star about 530 light-years away. The star is very old and has a concentration of heavy elements similar to solar abundance. [5] A survey in 2015 detected very strong starspot activity on HAT-P-18. [7]

Planetary system

In 2010 a transiting hot Saturn-sized planet was detected. [3] Its equilibrium temperature is 841 K. [8]

In 2014, observations utilizing the Rossiter–McLaughlin effect detected an exoplanet, HAT-P-18b, on a retrograde orbit, with an angle between orbital plane of the planet and the parent star equatorial plane equal to 132±15°. [9]

Transit-timing variation measurements in 2015 did not detect additional planets in the system. [10]

In 2016, the transmission optical spectra of the planet indicated that the atmosphere is lacking detectable clouds or hazes, and is blue in color due to Rayleigh scattering of light. [11] The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years. [12] By contrast, spectra taken in 2022 showed extensive haze and clear evidence of water vapour, along with the tail of escaping helium. [13]

The dayside temperature of HAT-P-18b was measured in 2019 to be 1004+78
−94 K. [14]

Size comparison of HAT-P-18 b and Jupiter Exoplanet Comparison HAT-P-18 b.png
Size comparison of HAT-P-18 b and Jupiter
The HAT-P-18 planetary system [3]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b0.183+0.034
−0.032  MJ 		0.04649±5.508029±0.00000420.106+0.15
−0.084		88.79±0.21° 0.947±0.044  RJ

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific . 99 (617): 695. Bibcode:1987PASP...99..695R. doi: 10.1086/132034 . Constellation record for this object at VizieR.
  2. 1 2 3 4 5 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. 1 2 3 Hartman, J. D.; Bakos, G. Á.; Sato, B.; Torres, G.; Noyes, R. W.; Latham, D. W.; Kovács, G.; Fischer, D. A.; Howard, A. W.; Johnson, J. A.; Marcy, G. W.; Buchhave, L. A.; Füresz, G.; Perumpilly, G.; Béky, B.; Stefanik, R. P.; Sasselov, D. D.; Esquerdo, G. A.; Everett, M.; Csubry, Z.; Lázár, J.; Papp, I.; Sári, P. (2010), "HAT-P-18b and HAT-P-19b: Two Low-Density Saturn-Mass Planets Transiting Metal-Rich K Stars", The Astrophysical Journal, 726: 52, arXiv: 1007.4850 , doi:10.1088/0004-637X/726/1/52, S2CID   10896305
  4. ↑ Wang, Xian-Yu; et al. (1 July 2021). "Transiting Exoplanet Monitoring Project (TEMP). VI. The Homogeneous Refinement of System Parameters for 39 Transiting Hot Jupiters with 127 New Light Curves". The Astrophysical Journal Supplement Series. 255 (1) 15. arXiv: 2105.14851 . Bibcode: 2021ApJS..255...15W . doi: 10.3847/1538-4365/ac0835 . S2CID   235253975.
  5. 1 2 3 4 5 Everett, Mark E.; Howell, Steve B.; Silva, David R.; Szkody, Paula (2013), "Spectroscopy of Faint Kepler Mission Exoplanet Candidate Host Stars", The Astrophysical Journal, 771 (2): 107, arXiv: 1305.0578 , Bibcode:2013ApJ...771..107E, doi:10.1088/0004-637X/771/2/107, S2CID   119270620
  6. ↑ HAT-P-18 -- Star
  7. ↑ Piskorz, Danielle; Knutson, Heather A.; Ngo, Henry; Muirhead, Philip S.; Batygin, Konstantin; Crepp, Justin R.; Hinkley, Sasha; Morton, Timothy D. (2015), "Friends of Hot Jupiters. III. An Infrared Spectroscopic Search for Low-Mass Stellar Companions", The Astrophysical Journal, 814 (2): 148, arXiv: 1510.08062 , Bibcode:2015ApJ...814..148P, doi:10.1088/0004-637X/814/2/148, S2CID   11525988
  8. ↑ Planet HAT-P-18 b at exoplanets.eu
  9. ↑ Esposito, M.; Covino, E.; Mancini, L.; Harutyunyan, A.; Southworth, J.; Biazzo, K.; Gandolfi, D.; Lanza, A. F.; Barbieri, M.; Bonomo, A. S.; Borsa, F.; Claudi, R.; Cosentino, R.; Desidera, S.; Gratton, R.; Pagano, I.; Sozzetti, A.; Boccato, C.; Maggio, A.; Micela, G.; Molinari, E.; Nascimbeni, V.; Piotto, G.; Poretti, E.; Smareglia, R. (2014), "The GAPS Programme with HARPS-N at TNG. III: The retrograde orbit of HAT-P-18b", Astronomy and Astrophysics, 564, arXiv: 1403.6728 , Bibcode:2014A&A...564L..13E, doi:10.1051/0004-6361/201423735, S2CID   59939759
  10. ↑ Seeliger, M.; Kitze, M.; Errmann, R.; Richter, S.; Ohlert, J. M.; Chen, W. P.; Guo, J. K.; Göğüş, E.; Güver, T.; Aydın, B.; Mottola, S.; Hellmich, S.; Fernandez, M.; Aceituno, F. J.; Dimitrov, D.; Kjurkchieva, D.; Jensen, E.; Cohen, D.; Kundra, E.; Pribulla, T.; Vaňko, M.; Budaj, J.; Mallonn, M.; Wu, Z.-Y.; Zhou, X.; Raetz, St.; Adam, C.; Schmidt, T. O. B.; Ide, A.; et al. (2015), "Ground-based transit observations of the HAT-P-18, HAT-P-19, HAT-P-27/WASP40 and WASP-21 systems", Monthly Notices of the Royal Astronomical Society, 451 (4): 4060–4072, arXiv: 1508.06215 , doi: 10.1093/mnras/stv1187 , S2CID   56034663
  11. ↑ Kirk, J.; Wheatley, P. J.; Louden, T.; Doyle, A. P.; Skillen, I.; McCormac, J.; Irwin, P. G. J.; Karjalainen, R. (2016), "Rayleigh scattering in the transmission spectrum of HAT-P-18b", Monthly Notices of the Royal Astronomical Society, 468 (4): 3907–3916, arXiv: 1611.06916 , doi: 10.1093/mnras/stx752 , S2CID   1058289
  12. ↑ Paragas, Kimberly; Vissapragada, Shreyas; Knutson, Heather A.; Oklopčić, Antonija; Chachan, Yayaati; Greklek-Mckeon, Michael; Dai, Fei; Tinyanont, Samaporn; Vasisht, Gautam (2021), "Metastable Helium Reveals an Extended Atmosphere for the Gas Giant HAT-P-18b", The Astrophysical Journal Letters, 909 (1): L10, arXiv: 2102.08392 , Bibcode:2021ApJ...909L..10P, doi: 10.3847/2041-8213/abe706 , S2CID   231942657
  13. ↑ Fu, Guangwei; Espinoza, Néstor; Sing, David K.; Lothringer, Joshua D.; Dos Santos, Leonardo A.; Rustamkulov, Zafar; Deming, Drake; Kempton, Eliza M.-R.; Komacek, Thaddeus D.; Knutson, Heather A.; Albert, Loïc; Pontoppidan, Klaus; Volk, Kevin; Filippazzo, Joseph (2022), "Water and an Escaping Helium Tail Detected in the Hazy and Methane-depleted Atmosphere of HAT-P-18b from JWST NIRISS/SOSS", The Astrophysical Journal Letters, 940 (2): L35, arXiv: 2211.13761 , Bibcode:2022ApJ...940L..35F, doi: 10.3847/2041-8213/ac9977 , S2CID   254017890
  14. ↑ Wallack, Nicole L.; Knutson, Heather A.; Morley, Caroline V.; Moses, Julianne I.; Thomas, Nancy H.; Thorngren, Daniel P.; Deming, Drake; Désert, Jean-Michel; Fortney, Jonathan J.; Kammer, Joshua A. (2019), "Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets UsingSpitzer Secondary Eclipses", The Astronomical Journal, 158 (6): 217, arXiv: 1908.00014 , Bibcode:2019AJ....158..217W, doi: 10.3847/1538-3881/ab2a05 , S2CID   199064423


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