Astronomy:HAT-P-18

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Short description: Star in the constellation Hercules
HAT-P-18
Observation data
Equinox J2000.0]] (ICRS)
Constellation Hercules
Right ascension  17h 05m 23.1475s[1]
Declination +33° 00′ 44.940″[1]
Apparent magnitude (V) 12.759[2]
Characteristics
Spectral type K2V
Astrometry
Radial velocity (Rv)-11.83 km/s
Proper motion (μ) RA: −14.002(9)[1] mas/yr
Dec.: −36.751(11)[1] mas/yr
Parallax (π)6.1863 ± 0.0093[1] mas
Distance527.2 ± 0.8 ly
(161.6 ± 0.2 pc)
Details[3]
Mass0.750+0.015−0.014 M☉
Radius0.7202+0.0095−0.01 R☉
Luminosity0.27±0.04[4] L☉
Surface gravity (log g)4.599±0.013 cgs
Temperature4835+39−35 K
Metallicity0.044+0.060−0.051
Rotation14.66±0.03 d[4]
Rotational velocity (v sin i)0.5±0.5[4] km/s
Age12.4+4.4−6.4[4] Gyr
Other designations
Gaia DR2 1334573817793362560, GSC 02594-00646, 2MASS J17052315+3300450[5]
Database references
SIMBADdata

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.[4] A survey in 2015 detected very strong starspot activity on HAT-P-18.[6]

Planetary system

In 2010 a transiting hot Saturn-sized planet was detected.[2] Its equilibrium temperature is 841 K.[7]

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°.[8]

Transit-timing variation measurements in 2015 did not detect additional planets in the system.[9]

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.[10] The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years.[11] By contrast, spectra taken in 2022 has showed an extensive hazes and clear evidence of water vapour, along with the tail of escaping helium.[12]

The dayside temperature of HAT-P-18b was measured in 2019 to be 1004+78−94 K.[13]

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. ↑ 1.0 1.1 1.2 1.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 Hartman, J. D.; Bakos, G. Á.; Sato, B.; Torres, G.; Noyes, R. W.; Latham, D. W.; Kovács, G.; Fischer, D. A. et al. (2010), "HAT-P-18b and HAT-P-19b: Two Low-Density Saturn-Mass Planets Transiting Metal-Rich K Stars", The Astrophysical Journal 726: 52, doi:10.1088/0004-637X/726/1/52 
  3. ↑ 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). doi:10.3847/1538-4365/ac0835. Bibcode: 2021ApJS..255...15W. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 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, doi:10.1088/0004-637X/771/2/107, Bibcode: 2013ApJ...771..107E 
  5. ↑ HAT-P-18 -- Star
  6. ↑ 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, doi:10.1088/0004-637X/814/2/148, Bibcode: 2015ApJ...814..148P 
  7. ↑ Planet HAT-P-18 b at exoplanets.eu
  8. ↑ Esposito, M.; Covino, E.; Mancini, L.; Harutyunyan, A.; Southworth, J.; Biazzo, K.; Gandolfi, D.; Lanza, A. F. et al. (2014), "The GAPS Programme with HARPS-N at TNG. III: The retrograde orbit of HAT-P-18b", Astronomy and Astrophysics 564, doi:10.1051/0004-6361/201423735, Bibcode: 2014A&A...564L..13E 
  9. ↑ Seeliger, M.; Kitze, M.; Errmann, R.; Richter, S.; Ohlert, J. M.; Chen, W. P.; Guo, J. K.; Göğüş, E. 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, doi:10.1093/mnras/stv1187 
  10. ↑ 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, doi:10.1093/mnras/stx752 
  11. ↑ Paragas, Kimberly; Vissapragada, Shreyas; Knutson, Heather A.; Oklopčić, Antonija; Chachan, Yayaati; Greklek-Mckeon, Michael; Dai, Fei; Tinyanont, Samaporn et al. (2021), "Metastable Helium Reveals an Extended Atmosphere for the Gas Giant HAT-P-18b", The Astrophysical Journal Letters 909 (1): L10, doi:10.3847/2041-8213/abe706, Bibcode: 2021ApJ...909L..10P 
  12. ↑ Fu, Guangwei; Espinoza, Néstor; Sing, David K.; Lothringer, Joshua D.; Dos Santos, Leonardo A.; Rustamkulov, Zafar; Deming, Drake; Kempton, Eliza M.-R. et al. (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, doi:10.3847/2041-8213/ac9977, Bibcode: 2022ApJ...940L..35F 
  13. ↑ Wallack, Nicole L.; Knutson, Heather A.; Morley, Caroline V.; Moses, Julianne I.; Thomas, Nancy H.; Thorngren, Daniel P.; Deming, Drake; Désert, Jean-Michel et al. (2019), "Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets UsingSpitzer Secondary Eclipses", The Astronomical Journal 158 (6): 217, doi:10.3847/1538-3881/ab2a05, Bibcode: 2019AJ....158..217W 

Coordinates: Sky map 17h 05m 23.1476s, +33° 00′ 44.9391″




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