HAT-P-18

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.[3] A survey in 2015 detected very strong starspot activity on HAT-P-18.[4]

HAT-P-18
Observation data
Epoch J2000      Equinox J2000
Constellation Hercules
Right ascension 17h 05m 23.1476s[1]
Declination +33° 00′ 44.9391″[1]
Apparent magnitude (V) 12.759[2]
Characteristics
Spectral type K2V
Astrometry
Radial velocity (Rv)-11.83 km/s
Proper motion (μ) RA: -14.073 mas/yr
Dec.: -36.689 mas/yr
Parallax (π)6.1669 ± 0.0231[1] mas
Distance529 ± 2 ly
(162.2 ± 0.6 pc)
Details[3]
Mass0.770±0.031 M☉
Radius0.749±0.037 R☉
Luminosity0.27±0.04 L☉
Surface gravity (log g)4.72 cgs
Temperature4857 K
Metallicity-0.05
Rotation14.66±0.03 d
Rotational velocity (v sin i)0.5±0.5 km/s
Age12.4+4.4
−6.4 Gyr
Other designations
Gaia DR2 1334573817793362560, GSC 02594-00646, 2MASS J17052315+3300450[1]
Database references
SIMBADdata

Planetary system

In 2010 a transiting hot Saturn-sized planet was detected.[2] Its equilibrium temperature is 841 K.[5]

In 2014, observations utilizing a 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°.[6]

The transit-timing variation measurements in 2015 did not detect additional planets in the system.[7]

In 2016, the transmission optical spectra of planet indicated that the atmosphere is lacking detectable clouds or hazes, and is blue in color due Rayleigh scattering of light.[8]

The dayside temperature of the HAT-P-18b was measured in the 2019 to be 1004+78
−94 K.[9]

Size comparison of HAT-P-18 b and Jupiter
The HAT-P-18 planetary system[2]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 0.183+0.034
−0.032 MJ		 0.04649± 5.508029±0.0000042 0.106+0.15
−0.084		 88.79±0.21° 0.947±0.044 RJ

References
  1. HAT-P-18 -- Star
  2. 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
  3. 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, doi:10.1088/0004-637X/771/2/107, S2CID 119270620
  4. 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, doi:10.1088/0004-637X/814/2/148, S2CID 11525988
  5. Planet HAT-P-18 b at exoplanets.eu
  6. 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, arXiv:1403.6728, doi:10.1051/0004-6361/201423735, S2CID 59939759
  7. 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
  8. 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
  9. 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, doi:10.3847/1538-3881/ab2a05, S2CID 199064423

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