View source for HAT-P-18

{{Short description|Star in the constellation Hercules}}
{{Starbox begin
| name = HAT-P-18
}}
{{Starbox observe
| epoch = J2000
| ra = {{RA|17|05|23.1475}}<ref name="Gaia DR3"/>
| dec = {{DEC|+33|00|44.940}}<ref name="Gaia DR3"/>
| constell = [[Hercules (constellation)|Hercules]]
| appmag_v = 12.759<ref name=Hartman2010/>
}}
{{Starbox character
| class = K2V
}}
{{Starbox astrometry
| radial_v = -11.83
| prop_mo_ra = {{val|−14.002|(9)}}
| prop_mo_dec = {{val|−36.751|(11)}}
| pm_footnote = <ref name="Gaia DR3"/>
| parallax = 6.1863
| p_error = 0.0093
| parallax_footnote = <ref name="Gaia DR3"/>
}}
{{Starbox detail
| source = <ref name="Wang2021"/>
| mass = 0.750{{±|0.015|0.014}}
| radius = 0.7202{{±|0.0095|0.01}}
| gravity = 4.599{{±|0.013}}
| luminosity = 0.27{{±|0.04}}<ref name=Everett2013>{{citation|arxiv=1305.0578|title=Spectroscopy of Faint Kepler Mission Exoplanet Candidate Host Stars|year=2013|doi=10.1088/0004-637X/771/2/107|last1=Everett|first1=Mark E.|last2=Howell|first2=Steve B.|last3=Silva|first3=David R.|last4=Szkody|first4=Paula|journal=The Astrophysical Journal|volume=771|issue=2|page=107|bibcode=2013ApJ...771..107E |s2cid=119270620}}</ref>
| temperature = 4835{{±|39|35}}
| metal = 0.044{{±|0.060|0.051}}
| rotation = 14.66{{±|0.03}} [[day|d]]<ref name=Everett2013/>
| rotational_velocity =0.5{{±|0.5}}<ref name=Everett2013/>
| age_gyr = 12.4{{±|4.4|6.4}}<ref name=Everett2013/>
}}
{{Starbox catalog
| names = {{odlist|GSC=02594-00646|2MASS=J17052315+3300450|Gaia DR2=1334573817793362560}}<ref name=simbad/>
}}
{{Starbox reference
| Simbad = HAT-P-18
}}
{{Starbox end}}
'''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.<ref name=Everett2013/>  A survey in 2015 detected very strong [[starspot]] activity on HAT-P-18.<ref>{{citation|arxiv=1510.08062|year=2015|doi=10.1088/0004-637X/814/2/148|last1=Piskorz|first1=Danielle|last2=Knutson|first2=Heather A.|last3=Ngo|first3=Henry|last4=Muirhead|first4=Philip S.|last5=Batygin|first5=Konstantin|last6=Crepp|first6=Justin R.|last7=Hinkley|first7=Sasha|last8=Morton|first8=Timothy D.|title=Friends of Hot Jupiters. III. An Infrared Spectroscopic Search for Low-Mass Stellar Companions|journal=The Astrophysical Journal|volume=814|issue=2|page=148|bibcode=2015ApJ...814..148P |s2cid=11525988}}</ref>
==Planetary system==
In 2010 a [[Transit (astronomy)|transiting]] hot Saturn-sized planet was detected.<ref name=Hartman2010>{{citation|arxiv=1007.4850|title=HAT-P-18b and HAT-P-19b: Two Low-Density Saturn-Mass Planets Transiting Metal-Rich K Stars|year=2010|doi=10.1088/0004-637X/726/1/52|last1=Hartman|first1=J. D.|last2=Bakos|first2=G. Á.|last3=Sato|first3=B.|last4=Torres|first4=G.|last5=Noyes|first5=R. W.|last6=Latham|first6=D. W.|last7=Kovács|first7=G.|last8=Fischer|first8=D. A.|last9=Howard|first9=A. W.|last10=Johnson|first10=J. A.|last11=Marcy|first11=G. W.|last12=Buchhave|first12=L. A.|last13=Füresz|first13=G.|last14=Perumpilly|first14=G.|last15=Béky|first15=B.|last16=Stefanik|first16=R. P.|last17=Sasselov|first17=D. D.|last18=Esquerdo|first18=G. A.|last19=Everett|first19=M.|last20=Csubry|first20=Z.|last21=Lázár|first21=J.|last22=Papp|first22=I.|last23=Sári|first23=P.|journal=The Astrophysical Journal|volume=726|page=52|s2cid=10896305}}</ref> Its equilibrium temperature is 841 [[Kelvin|K]].<ref>[https://exoplanet.eu/catalog/hat_p_18_b--723/ Planet HAT-P-18 b at exoplanets.eu]</ref>
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}}°.<ref>{{citation|arxiv=1403.6728|title=The GAPS Programme with HARPS-N at TNG. III: The retrograde orbit of HAT-P-18b|year=2014|doi=10.1051/0004-6361/201423735|last1=Esposito|first1=M.|last2=Covino|first2=E.|last3=Mancini|first3=L.|last4=Harutyunyan|first4=A.|last5=Southworth|first5=J.|last6=Biazzo|first6=K.|last7=Gandolfi|first7=D.|last8=Lanza|first8=A. F.|last9=Barbieri|first9=M.|last10=Bonomo|first10=A. S.|last11=Borsa|first11=F.|last12=Claudi|first12=R.|last13=Cosentino|first13=R.|last14=Desidera|first14=S.|last15=Gratton|first15=R.|last16=Pagano|first16=I.|last17=Sozzetti|first17=A.|last18=Boccato|first18=C.|last19=Maggio|first19=A.|last20=Micela|first20=G.|last21=Molinari|first21=E.|last22=Nascimbeni|first22=V.|last23=Piotto|first23=G.|last24=Poretti|first24=E.|last25=Smareglia|first25=R.|journal=Astronomy and Astrophysics |volume=564 |bibcode=2014A&A...564L..13E |s2cid=59939759}}</ref>
[[Transit-timing variation]] measurements in 2015 did not detect additional planets in the system.<ref>{{citation|arxiv=1508.06215|title=Ground-based transit observations of the HAT-P-18, HAT-P-19, HAT-P-27/WASP40 and WASP-21 systems|year=2015|doi=10.1093/mnras/stv1187|last1=Seeliger|first1=M.|last2=Kitze|first2=M.|last3=Errmann|first3=R.|last4=Richter|first4=S.|last5=Ohlert|first5=J. M.|last6=Chen|first6=W. P.|last7=Guo|first7=J. K.|last8=Göğüş|first8=E.|last9=Güver|first9=T.|last10=Aydın|first10=B.|last11=Mottola|first11=S.|last12=Hellmich|first12=S.|last13=Fernandez|first13=M.|last14=Aceituno|first14=F. J.|last15=Dimitrov|first15=D.|last16=Kjurkchieva|first16=D.|last17=Jensen|first17=E.|last18=Cohen|first18=D.|last19=Kundra|first19=E.|last20=Pribulla|first20=T.|last21=Vaňko|first21=M.|last22=Budaj|first22=J.|last23=Mallonn|first23=M.|last24=Wu|first24=Z.-Y.|last25=Zhou|first25=X.|last26=Raetz|first26=St.|last27=Adam|first27=C.|last28=Schmidt|first28=T. O. B.|last29=Ide|first29=A.|last30=Mugrauer|first30=M.|journal=Monthly Notices of the Royal Astronomical Society|volume=451|issue=4|pages=4060–4072|doi-access=free |s2cid=56034663|display-authors=29}}</ref>
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.<ref>{{citation|arxiv=1611.06916|title=Rayleigh scattering in the transmission spectrum of HAT-P-18b|year=2016|doi=10.1093/mnras/stx752|last1=Kirk|first1=J.|last2=Wheatley|first2=P. J.|last3=Louden|first3=T.|last4=Doyle|first4=A. P.|last5=Skillen|first5=I.|last6=McCormac|first6=J.|last7=Irwin|first7=P. G. J.|last8=Karjalainen|first8=R.|journal=Monthly Notices of the Royal Astronomical Society|volume=468|issue=4|pages=3907–3916|doi-access=free |s2cid=1058289}}</ref> The atmosphere seems to gradually evaporate, but at a slow rate - less than 2% of planetary mass is lost per one billion years.<ref>{{citation|arxiv=2102.08392|year=2021|title=Metastable Helium Reveals an Extended Atmosphere for the Gas Giant HAT-P-18b|doi=10.3847/2041-8213/abe706|last1=Paragas|first1=Kimberly|last2=Vissapragada|first2=Shreyas|last3=Knutson|first3=Heather A.|last4=Oklopčić|first4=Antonija|last5=Chachan|first5=Yayaati|last6=Greklek-Mckeon|first6=Michael|last7=Dai|first7=Fei|last8=Tinyanont|first8=Samaporn|last9=Vasisht|first9=Gautam|journal=The Astrophysical Journal Letters|volume=909|issue=1 |pages=L10|bibcode=2021ApJ...909L..10P |s2cid=231942657 |doi-access=free }}</ref> By contrast, spectra taken in 2022 has showed an extensive hazes and clear evidence of water vapour, along with the tail of escaping helium.<ref>{{citation|arxiv=2211.13761|year=2022|title=Water and an Escaping Helium Tail Detected in the Hazy and Methane-depleted Atmosphere of HAT-P-18b from JWST NIRISS/SOSS|doi=10.3847/2041-8213/ac9977 |last1=Fu |first1=Guangwei |last2=Espinoza |first2=Néstor |last3=Sing |first3=David K. |last4=Lothringer |first4=Joshua D. |last5=Dos Santos |first5=Leonardo A. |last6=Rustamkulov |first6=Zafar |last7=Deming |first7=Drake |last8=Kempton |first8=Eliza M.-R. |last9=Komacek |first9=Thaddeus D. |last10=Knutson |first10=Heather A. |last11=Albert |first11=Loïc |last12=Pontoppidan |first12=Klaus |last13=Volk |first13=Kevin |last14=Filippazzo |first14=Joseph |journal=The Astrophysical Journal Letters |volume=940 |issue=2 |pages=L35 |bibcode=2022ApJ...940L..35F |s2cid=254017890 |doi-access=free }}</ref>
The dayside temperature of HAT-P-18b was measured in 2019 to be 1004{{±|78|94}} [[Kelvin|K]].<ref>{{citation|arxiv=1908.00014|year=2019|doi=10.3847/1538-3881/ab2a05|last1=Wallack|first1=Nicole L.|last2=Knutson|first2=Heather A.|last3=Morley|first3=Caroline V.|last4=Moses|first4=Julianne I.|last5=Thomas|first5=Nancy H.|last6=Thorngren|first6=Daniel P.|last7=Deming|first7=Drake|last8=Désert|first8=Jean-Michel|last9=Fortney|first9=Jonathan J.|last10=Kammer|first10=Joshua A.|title=Investigating Trends in Atmospheric Compositions of Cool Gas Giant Planets UsingSpitzer ''Secondary'' Eclipses|journal=The Astronomical Journal|volume=158|issue=6|page=217|bibcode=2019AJ....158..217W |s2cid=199064423 |doi-access=free }}</ref>
[[File:Exoplanet Comparison HAT-P-18 b.png|left|thumb|200px|Size comparison of ''HAT-P-18 b'' and Jupiter]]
{{OrbitboxPlanet begin
| table_ref = <ref name=Hartman2010/>
}}
{{OrbitboxPlanet
| exoplanet = b
| mass = 0.183{{±|0.034|0.032}}
| radius =  0.947{{±|0.044}}
| semimajor = 0.04649{{±||0.00062|0.00059}}
| period =  5.508029{{±|0.0000042}}
| eccentricity = 0.106{{±|0.15|0.084|}}
| inclination = 88.79{{±|0.21}}
}}
{{Orbitbox end}}
==References==
{{Reflist|refs=
<ref name="Gaia DR3">{{Cite Gaia DR3|4224259562941398400}}</ref>
<ref name=simbad>[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HAT-P-18 HAT-P-18 -- Star]</ref>
<ref name="Wang2021">{{cite journal | title=Transiting Exoplanet Monitoring Project (TEMP). VI. The Homogeneous Refinement of System Parameters for 39 Transiting Hot Jupiters with 127 New Light Curves | last1=Wang | first1=Xian-Yu | last2=Wang | first2=Yong-Hao | last3=Wang | first3=Songhu | last4=Wu | first4=Zhen-Yu | last5=Rice | first5=Malena | last6=Zhou | first6=Xu | last7=Hinse | first7=Tobias C. | last8=Liu | first8=Hui-Gen | last9=Ma | first9=Bo | last10=Peng | first10=Xiyan | last11=Zhang | first11=Hui | last12=Yu | first12=Cong | last13=Zhou | first13=Ji-Lin | last14=Laughlin | first14=Gregory | display-authors=1 | journal=The Astrophysical Journal Supplement Series | date=1 July 2021 | volume=255 | issue=1 | article-number=15 | page=<!-- to prevent citation bot adding nonexistent page number--> | arxiv=2105.14851 | bibcode=2021ApJS..255...15W | bibcode-access=free | doi=10.3847/1538-4365/ac0835 | s2cid=235253975 | doi-access=free }}</ref>
}}
{{Sky|17|05|23.1476|+|33|00|44.9391}}
{{Hercules (constellation)}}
{{DEFAULTSORT:HAT-P-18}}
[[Category:Hercules (constellation)]]
[[Category:K-type main-sequence stars]]
[[Category:Planetary systems with one confirmed planet]]
[[Category:Planetary transit variables]]
[[Category:2MASS objects|J17052315+3300450]]
{{main-star-stub}}
{{extrasolar-planet-stub}}