Theoretical Spectra and Light Curves of Close-in E

arXiv:0709.4080v2[astro-ph]26Jan2008AcceptedtoAp.J.PreprinttypesetusingLATEXstyleemulateapjv.10/09/06THEORETICALSPECTRAANDLIGHTCURVESOFCLOSE-INEXTRASOLARGIANTPLANETSANDCOMPARISONWITHDATAA.Burrows1,J.Budaj1,2&I.Hubeny1AcceptedtoAp.J.ABSTRACTWepresenttheoreticalatmosphere,spectral,andlight-curvemodelsforextrasolargiantplanets(EGPs)undergoingstrongirradiationforwhichSpitzerplanet/starcontrastratiosorlightcurveshavebeenpublished(circaJune2007).TheseincludeHD209458b,HD189733b,TrES-1,HD149026b,HD179949b,andυAndb.Bycomparingmodelswithdata,wefindthatanumberofEGPatmospheresexperiencethermalinversionsandhavestratospheres.ThisisparticularlytrueforHD209458b,HD149026b,andυAndb.Thisfindingtranslatesintoqualitativechangesintheplanet/starcontrastratiosatsecondaryeclipseandinclose-inEGPorbitallightcurves.Moreover,thepresenceofatmo-sphericwaterinabundanceisfullyconsistentwithalltheSpitzerdataforthemeasuredplanets.Forplanetswithstratospheres,waterabsorptionfeaturesinvertintoemissionfeaturesandmid-infraredfluxescanbeenhancedbyafactoroftwo.Inaddition,thecharacterofnear-infraredplanetaryspectracanberadicallyaltered.Wederiveacorrelationbetweentheimportanceofsuchstratospheresandthestellarfluxontheplanet,suggestingthatclose-inEGPsbifurcateintotwogroups:thosewithandwithoutstratospheres.FromthefindingthatTrES-1showsnosignsofastratosphere,whileHD209458bdoes,weestimatethemagnitudeofthisstellarfluxbreakpoint.Wefindthattheheatredistributionparameter,Pn,forthefamilyofclose-inEGPsassumesvaluesfrom∼0.1to∼0.4.ThispaperprovidesabroadtheoreticalcontextforthefuturedirectcharacterizationofEGPsintightorbitsaroundtheirilluminatingstars.Subjectheadings:stars:individual(HD209458,HD189733,TrES-1,HD149026,υAnd,HD179949)—(stars:)planetarysystems—planetsandsatellites:general1.INTRODUCTIONTodate,morethan250extrasolarplanetshavebeendiscoveredandmorethan29ofthemaretransitingtheirprimarystar3.Onetransitingplanetisa“Neptune”(GJ436b),buttherestaregiantplanetswithanimpressivelywiderangeofmassesandradiithatspeaktothehetero-geneityofthefamilyofclose-inEGPs(ExtrasolarGiantPlanets).Table1liststhesetransitingEGPsandsomeoftheirrelevantproperties,alongwithmanyoftheref-erencestotheobservationalanddiscoverypapersfromwhichthesedataweretaken.Table2listsusefuldataforthecorrespondingprimarystars,includingtheirmasses,luminosities,radii,andapproximateages.Bothtablesareinorderofincreasingplanetarysemi-majoraxisand,consideringthepaceofthefield,bothshouldbeconsid-eredprovisional.Notshownaretheeccentricities,whicharegenerallysmall,butwhichforHAT-P-2b,GJ436b,andXO-3bare∼0.507,∼0.14,and∼0.22,respectively.Forthesethreeclose-inEGPs,significanttidalheatingand,perhaps,forcingbyanunseencompanionareim-plied.Radial-velocitymeasurementsforanon-transitingEGPprovidealowerlimittoitsmass,butlittleelse.1DepartmentofAstronomyandStewardObserva-tory,TheUniversityofArizona,Tucson,AZ85721;[e-mail],[e-mail],[e-mail]2AstronomicalInstitute,TatranskaLomnica,05960SlovakRepublic3SeeJ.Schneider’sExtrasolarPlanetEncyclopaediaat://exoplanets.eu,andtheCarnegie/Californiacompilationat’masses.Thesedataprovidephysicalconstraintswithwhichde-tailedevolutionaryandstructuralmodelsthatincorpo-rateirradiationandmigrationcanbetested(see,e.g.,Burrowsetal.2007a;Guillotetal.2006).Withsu-perbphotometricaccuracy,thewavelength-dependenceofthetransitradiicaninprincipleprovideameasureofaplanet’satmosphericcomposition(Fortneyetal.2003).Inthisway,sodiumhasbeendetectedinHD209458b(Charbonneauetal.2002)andwaterhasbeenidentifiedinbothHD189733b(Tinettietal.2007,butseeEhrenreichetal.2007)andHD209458b(Barman2007).Moreover,high-precisionopticalphotometryhasconstrained(perhaps,measured)thegeometricalbedooftheclose-inEGPHD209458b(Roweetal.2006,2007).HD209458b’sopticalalbedoisverylow(∼3.8±4.5%),inkeepingwiththepredictionsofSudarskyetal.(2000)whenthealkalimetals,andnotclouds,dominateab-sorptionintheatmosphereandRayleighscatteringdom-inatesscattering.Nevertheless,usingcurrenttechnology,transitmea-surementshavelimitedutilityincharacterizingtheatmo-spheresandcompositionsoftheseplanets.Astronomersrequiremoredirectdetectionsoftheplanet’sspectrumtoprobeitschemistryandatmosphericproperties.ThisisinthetraditionofremotesensinginthesolarsystemandoftheEarth.Untilrecently,ithadbeenthoughtthatthelightfromanextrasolarplanethadtobeseparatedfromundertheglareofitsparentstarusinghigh-angularreso-lution,extremelyhigh-contrastimaging.Thisisstillthecaseintheopticalforthecool“wide-separation”EGPs(Burrowsetal.2004;Sudarskyetal.2005;Burrows22005)andterrestrialplanets,forwhichtheplanet-starcontrastratiois∼10−9to∼10−10,butsuchperformancehasnotyetbeendemonstrated.However,forthehotclose-inEGPs,theplanet-starcontrastratiosinthemid-infraredaremuchmorefa-vorable(Burrows,Sudarsky,&Hubeny2003,2004),of-timesexceeding10−3.Thiscapabilityhasledtoabreak-throughinthestudyofexoplane