HAT-P-18#Planetary system

In 2010 a transiting hot Saturn-sized planet was detected.{{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}} Its equilibrium temperature is 841 K.[https://exoplanet.eu/catalog/hat_p_18_b--723/ Planet HAT-P-18 b at exoplanets.eu]

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}}°.{{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}}

Transit-timing variation measurements in 2015 did not detect additional planets in the system.{{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}}

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

The dayside temperature of HAT-P-18b was measured in 2019 to be 1004{{±|78|94}} K.{{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 }}

File:Exoplanet Comparison HAT-P-18 b.png

{{OrbitboxPlanet begin

| table_ref =

}}

{{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}}

{{Reflist|refs=

{{Cite Gaia DR3|4224259562941398400}}

{{Cite constellation|HAT-P-18}}

[http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HAT-P-18 HAT-P-18 -- Star]

{{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= | arxiv=2105.14851 | bibcode=2021ApJS..255...15W | bibcode-access=free | doi=10.3847/1538-4365/ac0835 | s2cid=235253975 | doi-access=free }}

}}

{{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

J17052315+3300450

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