A dayside thermal inversion in the atmosphere of WASP-19b
A. S. Rajpurohit, F. Allard, D. Homeier, O. Mousis, S. Rajpurohit
AAstronomy & Astrophysics manuscript no. aa_wasp-19 c (cid:13)
ESO 2020August 13, 2020
A dayside thermal inversion in the atmosphere of WASP-19b
A. S. Rajpurohit , F. Allard , D. Homeier , O. Mousis , S. Rajpurohit Astronomy & Astrophysics Division, Physical Research Laboratory, Navrangapura, Ahmedabad 380009, Indiae-mail: [email protected] Univ Lyon, Ens de Lyon, Univ Lyon1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France Förderkreis Planetarium Göttingen e.V., Nordhäuser Weg 18, 37085, Göttingen, Germany Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388, Marseille, France The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USAReceived September 15, 1996; accepted March 16, 1997
ABSTRACT
Context.
Observations of ultra-hot Jupiters indicate the existence of thermal inversion in their atmospheres with dayside temperaturesgreater than 2200 K. Various physical mechanisms such as non-local thermal equilibrium, cloud formation, disequilibrium chemistry,ionisation, hydrodynamic waves and associated energy, have been omitted in previous spectral retrievals while they play an importantrole on the thermal structure of their upper atmospheres.
Aims.
We aim at exploring the atmospheric properties of WASP-19b to understand its largely featureless thermal spectra using astate-of-the-art atmosphere code that includes a detailed treatment of the most important physical and chemical processes at play insuch atmospheres.
Methods.
We used the one-dimensional line-by-line radiative transfer code
PHOENIX in its spherical symmetry configuration includingthe BT-Settl cloud model and C / O disequilibrium chemistry to analyse the observed thermal spectrum of WASP-19b.
Results.
We find evidence for a thermal inversion in the dayside atmosphere of the highly irradiated ultra-hot Jupiter WASP-19bwith T eq ∼ O dissociates thermally at pressure below 10 − bar. The invertedtemperature-pressure profiles of WASP-19b show the evidence of CO emission features at 4.5 µ m in its secondary eclipse spectra. Conclusions.
We find that the atmosphere of WASP-19b is thermally inverted. We infer that the thermal inversion is due to the strongimpinging radiation. We show that H O is partially dissociated in the upper atmosphere above about τ = − , but is still a significantcontributor to the infrared-opacity, dominated by CO. The high-temperature and low-density conditions cause H O to have a flatteropacity profile than in non-irradiated brown dwarfs. Altogether these factors makes H O more di ffi cult to identify in WASP-19b. Wesuggest that state-of-the-art PHOENIX model atmosphere code is well-suited to the study of this new class of extrasolar planets, that isthe ultra-hot Jupiters.
Key words. planets and satellites : atmospheres, planets and satellites: gaseous planets, radiative transfer
1. Introduction
More than 4000 exoplanets have been discovered so far via de-tection techniques such as the transit and radial velocity meth-ods. A large number of them falls into the category of hotJupiters and are normally found around around A, F and G typestars (Zellem et al. 2017). In recent times, a new class of ultra-hot Jupiters has also been identified. Due to their close proxim-ity to their host star, these ultra-hot Jupiters show distinct char-acteristics compared with hot Jupiters, such as a higher rate oftransit and eclipse. Ultra-hot Jupiters with an orbital separationof less than 0.05 AU face the highest level of irradiation fromtheir host stars. With large atmospheric scale heights they dis-play dayside temperatures ≥ , C H , and HCN (Madhusudhan 2012). Recent study byLothringer et al. (2018) showed that various atomic and molec-ular species such as O, C, N, Fe, Mg, H O, CO, CH , N , NH including SiO and metal hydrides are also present at high tem-perature in the atmospheres of hot Jupiters.Wavelength dependence of the transit radii observations pro-vides a measure of a planet’s atmospheric composition (Fortneyet al. 2003). For example, atomic sodium is detected from thetransit radii observations of hot-Jupiter HD209458b (Charbon-neau et al. 2002) whereas H O has been detected in the atmo-sphere of both HD189733b (Tinetti et al. 2007) and HD209458b(Barman 2007). Observations of ultra-hot Jupiters have also re-vealed information about the thermal structure of their atmo-spheres (Madhusudhan et al. 2014).Depending on the presence of inverted or non-inverted ther-mal structure profile of their atmospheres, ultra-hot Jupiters candisplay emission or absorption features in their spectra. Theymay also show a blackbody spectrum in presence of an isother-mal profile (Fortney et al. 2008; Line & Parmentier 2016). Thenature of the absorbers responsible for the thermal inversion intheir atmospheres is not yet known, though the presence of vana-dium oxide (VO) and titanium oxide (TiO) has been proposed tobe cause for this (Burrows et al. 2008; Fortney et al. 2008). Theobserved absorption broadband features in their optical trans-mission spectrum between 0.62 and 0.8 µ m can possibly be ex-plained by these absorbers (Désert et al. 2008). Processes such as Article number, page 1 of 5 a r X i v : . [ a s t r o - ph . E P ] A ug & A proofs: manuscript no. aa_wasp-19 vertical mixing that prevent the temperature inversion from oc-curring in their atmosphere are described by Spiegel et al. (2009)and Parmentier et al. (2013, 2016), whereas the role of stellar ac-tivity for the thermal inversion in the atmosphere of hot-Jupitersis studied by Knutson et al. (2010).Evidences for thermal inversion and diverse characteristicsof the atmospheres of ultra-hot Jupiters are also imprinted intheir near-infrared (NIR) observations. For example, TiO hasbeen detected as an emission feature in WASP-33b (Hayneset al. 2015; Nugroho et al. 2017) and as an absorption featurein WASP-19b (Sedaghati et al. 2017). Emission features due toH O and VO have also been detected in WASP-121b (Evanset al. 2017). The presence of thermal inversion without H O,TiO, and VO has been noticed in the low resolution secondaryeclipse spectra of WASP-18b (Sheppard et al. 2017; Arcangeliet al. 2018). Their study provides evidence for CO emission at4.5 µ m, implying an inverted thermal structure. On the otherhand, no clear evidence for emission or absorption features ofH O is found in HAT-P-7b (Mansfield et al. 2018), WASP-12b(Swain et al. 2013), and WASP-103b (Kreidberg et al. 2018).These planets show instead a thermal blackbody spectra. A hand-ful of extremely hot-Jupiters also do not show any hint for ther-mal inversion such as HD209458b, KELT-1b, and Kepler-13Ab(Diamond-Lowe et al. 2014; Beatty et al. 2017a,b).Retrieval techniques are commonly used to constrain thechemical composition, thermal structure, and to explain the fea-tureless spectra of ultra-hot Jupiters (Madhusudhan & Seager2009; Line et al. 2013; Stevenson et al. 2014). Such meth-ods allowed to detect the presence of CO with high C / O ra-tio in WASP-18b (Sheppard et al. 2017) and to derive a sub-solar metallicity associated with an oxygen-rich composition inWASP-33b (Haynes et al. 2015). The forward modelling ap-proach by Arcangeli et al. (2018), Lothringer et al. (2018), andParmentier et al. (2018) explains the lack of strong H O spec-tral features in the ultra-hot Jupiters due to molecular dissoci-ation. Considering H– opacity and the thermal dissociation ofH O, Arcangeli et al. (2018), Kreidberg et al. (2018), Kitzmannet al. (2018), and Mansfield et al. (2018) explained the feature-less spectra in some ultra-hot Jupiters for example HAT-P-7b,KELT-9b, WASP-12b, WASP-121b, and WASP-18b. Althoughthe retrieval techniques are useful to quantify the atmosphericabundances of ultra-hot Jupiters, the results demonstrate a largediversity in their chemical composition and thermal structures,which could lead to biased conclusions.In this paper, we investigate the atmospheric properties of theultra-hot Jupiter WASP-19b. WASP-19b is among the objectsthat exhibit weaker spectral features compared to their coolercounterparts. WASP-19b has a shorter orbital period and, thus,receives extreme irradiation from its host star. Its atmosphere isthen of particular interest to study. We argue that proper chem-istry and opacity play a key role in understanding its extreme hotatmosphere without invoking unusual abundances.
2. Model Construction
To model the atmosphere of WASP-19b, we have used the BT-Settl model atmosphere described in Allard et al. (2012) andRajpurohit et al. (2012). BT-Settl is a state-of-the-art model at-mosphere code which has been extremely successful to repro-duce the properties of stellar to sub-stellar objects including coolbrown dwarfs (Rajpurohit et al. 2012, 2013). The current ver-sion of the BT-Settl model uses H O along with other molec-ular line lists such as FeH, CrH, TiO, VO, CaH, NH , Mg,CO and CO. Collision induced absorption (CIA) from H col- lisions with H , He, CH , N , and Ar along with CO -CO , Ar-CH , and CH -CH are also included (for more detail see Allardet al. (2012)). The BT-Settl model accounts for many continu-ous opacity sources, including bound-free opacity from H, H–,He, C, N, O, Na, Mg, Al, Si, S, Ca, and Fe, free-free opacityfrom H, Mg, and Si, and scattering from e– , H, He, and H .The model includes the opacities of more than 100 molecularspecies, including many molecules, isotopes, atomic species andtheir ionised states. Detailed profiles for the alkali lines as de-scribed in Unsold (1968), Valenti & Piskunov (1996), and Allardet al. (2007) and approximation is utilised for the atomic damp-ing constants with a correction factor to the widths of 2.5 forthe non-hydrogenic atoms. Several important atomic transitions,such as the alkali, Ca I, and Ca II resonance lines along withmore accurate broadening data for neutral hydrogen collisionsby Barklem et al. (2000) have been included.The BT-Settl model also accounts for disequilibrium chem-istry for C / O and N (Graven & Long 1954; Visscher et al. 2010;Allard et al. 2012). The reference solar elemental abundances arederived from Ca ff au et al. (2011). These models are computedwith the version 15.5 of PHOENIX , a multi-purpose atmospherecode (Allard et al. 2001).
PHOENIX solves the radiative trans-fer in 1D spherical symmetry with irradiation such that flux isconserved at each layer. The basic assumption in
PHOENIX whilesolving radiative transfer is hydrostatic equilibrium with convec-tion using the mixing length theory, and a sampling treatment ofthe opacities (see Allard et al. 2013).The atmosphere model for WASP-19b irradiated by the hoststar of spectral type G5 with an orbital separation of 0.0163 AUhas been computed by considering boundary conditions as de-scribed in Barman et al. (2001). A pre-computed converged non-irradiated model structure at 400 K is chosen from Allard et al.(2012) as the initial model structure to start with. The tempera-ture is decreased down to 100 K to achieve the model structure.A temperature change of less than 1 K at every depth point inthe thermal structure is considered as the criterion for the con-verged model. E ff ective temperature ( T e ff ) of 5500 K, surfacegravity (log g ) of 4.5, and [M / H]) = f = + f measures the uniform heat redistribution where f = f = τ = − to 10 at the peak of the spectral energy distribution which correspondsto pressures of 10 − to ∼
10 bars. In the computation of the at-mospheric model, some non-local thermal equilibrium (NLTE)processes have also been included for a small set of elementsand level numbers (H I, He I, Li I, C I, Ni I, O I, Ne I, Na I, NaII, Mg I, Mg II, Si I, S I, K I, K II, Ca I, Ca II, Rb I), whicha ff ect the entire atmosphere. PHOENIX has been used to calcu-late both the planetary and stellar spectra from 10 to 10 Å. Theplanetary, star and orbital parameters used for the computationirradiated model of WASP-19b are summarised in Table 1.
3. Results and Discussion
A thermal spectrum of WASP-19b, from Anderson et al. (2010),Gibson et al. (2010), Burton et al. (2012), Anderson et al. (2013),Bean et al. (2013), and Lendl et al. (2013), is shown in Fig 1. Theplanet-to-star flux ratio at 4.5 µ m is higher than the one at 3.6 Article number, page 2 of 5. S. Rajpurohit , F. Allard , D. Homeier , O. Mousis , S. Rajpurohit: Atmosphere of WASP-19b µ m)0.0000.0020.0040.0060.0080.010 P l ane t − t o − S t a r − R a t i o [M/H]= − − − − − − − − − − − P ga s ( ba r) Fig. 1: Comparison of observed thermal spectra of WASP-19bwith the modelled spectra calculated using
PHOENIX (solid line)at di ff erent metallicity with an average dayside heat redistribu-tion ( f = µ m aredue to CO in presence of thermal inversion.Table 1: Planetary, stellar and orbital parameters used in themodel are from Butler et al. (2006), Southworth et al. (2007),Hebb et al. (2010) and Hellier et al. (2011).Parameter Value a [p] Jupiter )log g [p] / sec ] T int[p]
100 [K] T e ff [ (cid:63) ] g [ (cid:63) ] / sec ]R [ (cid:63) ] (cid:12) )[M / H] [ (cid:63) ] µ m Spitzer / IRAC channel. Moreover, at higher wavelengths,namely at 5.8 and 8.0 µ m, the planet-to-star flux ratio is evenhigher than 4.5 µ m. This clearly indicates the presence of excessemission in some photometric bands over others.The atmosphere of WASP-19b has been modelled with theparameters given in Table 1 using PHOENIX . It shows the pres-ence of thermal inversion (see inset diagram, Fig. 1) and theequilibrium temperature is found to be ∼ µ mis due to the presence of CO, which in turn is caused by thermalinversion that exists in the atmosphere. The corresponding pres-sure range, as probed by the secondary eclipse, is 10 − to 10 − bar. Previous studies on WASP-19b did not show any evidence ofthermal inversion in its atmosphere (Anderson et al. 2013; Beanet al. 2013). However, these studies were mainly based on re-trieval techniques where abundances and thermal structure werefitted to the data.We investigate the e ff ect of metallicity on the atmosphere ofWASP-19b by changing all the heavy-elemental abundances bya factor of two. As shown by the inset image of Fig. 1, the ther-mal inversion becomes stronger as the metallicity increases. Thisis mainly due to the temperature dependence of the thermal dis-sociation of various molecules, which changes the photosphericabundances ratio of TiO and H O at di ff erent metallicities (Par-mentier et al. 2018). At higher metallicities, the increase in theabundances of various absorbers such as TiO warms the upper at-mosphere. This causes the thermal inversion to be even strongeras compared to solar metallicity which leads to strong emissionfeatures of CO and shallower features of H O in their thermalspectra. We find that models with sub-solar metallicities showsignature of a very weak or no thermal inversion (see Fig. 1).This is a result of the decrease of TiO and VO abundances. Inmost of the hot Jupiters or massive planets, the metallicity is be-lieved to approach the metallicity of the host star (Torres et al.2012; Arcangeli et al. 2018). We also investigate this by com-paring the observed thermal spectra of the dayside atmosphereof WASP-19b with the models at [M / H] = -2.0, 0.0 and + dissociates in the upper atmosphere due to im-pinging radiation from about τ = − , but not enough to preventthe molecular hydrogen atmosphere. Due to the impinging radi-ation, free electrons are available and constant over most of theupper photosphere. Neutral atomic oxygen is fully locked to thevery stable CO molecule in the deep atmosphere ( P > − bar),but becomes as abundant as CO in the upper atmosphere. Thisis the result of partial dissociation of CO, and other oxygen–bearing molecules. While CO is quasi-constant throughout theatmosphere. We find that H and CO are the most abundantmolecules, while CO, TiO and VO are the most important molec-ular opacity sources in the atmosphere of WASP-19b.As shown Fig. 2 (left panels), we find that the variation ofatomic and molecular abundances, together with the strong im-pinging radiation, contribute to the thermal inversion in the at-mosphere of WASP-19b. At 0.0163 AU, the thermal structure ofWASP-19b is too hot for the formation of the BT-Settl clouds,whereas the presence of CO / CO reveals the disequilibriumchemistry. We find the formation of a limited amount of CO in disequilibrium chemistry, but not abundant enough to partic-ipate significantly in the CO and H O balance. We also showthat TiO and alkali doublets, seen in early to mid-type browndwarfs, are the main opacities in the optical to near-IR spectrumof WASP-19b. It is evident from Fig. 2 (right panels) that thetemperature inversion causes the wiggles in the concentrationsalong the structure causing CO bands to appear in emission.Figure 3 shows the synthetic spectra of WASP-19b in the op-tical at di ff erent metallicities. We see that despite extremely lowabundances, similar to brown dwarfs and irradiated hot-Jupiter Article number, page 3 of 5 & A proofs: manuscript no. aa_wasp-19
H H e- H- CO H O TiO+VO O CO − − − − − − − − − − − − − − Optical depth [ τ ]10 − − − − − − M i x i ng r a t i o [M/H]= +2.0 − − − − − − − − − − − − M i x i ng r a t i o [M/H]= +2.0 − − − − − − − − − − − − − − Optical depth [ τ ]10 − − − − − − M i x i ng r a t i o [M/H]= 0.0 − − − − − − M i x i ng r a t i o [M/H]= 0.0 − − − − − − − − − − − − − − − Optical depth [ τ ]10 − − − − − − − M i x i ng r a t i o [M/H]= − − − − − − − M i x i ng r a t i o [M/H]= − Fig. 2: Concentration of important absorbing molecules and neutral atoms as a function of optical depth and temperature at [M / H] =+ / H] = / H] = -2.0 (bottom). These species deplete at the given pressure range for the irradiated hotJupiter WASP-19b (see main text). The grey shaded region (left panels) corresponds to the structure inversion and shows the windowof the observable atmosphere from which most of the spectrum emerges (in the CO, H O, TiO molecular bands pseudo continuum).We notice that in the upper atmosphere ( τ < − ), H O, TiO and VO dissociate whereas neutral atomic oxygen remains constant.We find that CO remain constant throughout the atmosphere of WASP-19b. The temperature inversion (right panels) causes thewiggles along the structure causing CO bands to emerge in emission..atmospheres (Allard et al. 2001; Barman et al. 2001, 2002), theTiO cross-sections are strong enough to preserve TiO as the mainoptical to near-IR opacity, along with alkali atomic fundamentaltransitions. These are the most important opacity sources, to-gether with CO in the infrared, that survive the immense heatimpinging of the planet atmosphere. The thermal inversion po-tentially hides pseudo-continuum opacities such as H O, and the high temperatures do not allow triatomic to remain stable. Alsoat given resolution and at such high temperature conditions, H Ohas a much flatter opacity profile making it more di ffi cult torecognise, especially at those spectral resolutions. Article number, page 4 of 5. S. Rajpurohit , F. Allard , D. Homeier , O. Mousis , S. Rajpurohit: Atmosphere of WASP-19b µ m)0.00000.00020.00040.00060.00080.0010 P l ane t − t o − S t a r − R a t i o [M/H]=+2.0[M/H]=0.0[M/H]= − − − Na TiO
TiO
TiO Na K Fig. 3: Synthetic spectra of WASP-19b in the optical range cal-culated using
PHOENIX at di ff erent metallicities with an averagedayside heat redistribution (f =
4. Conclusions
We have used the state-of-the-art 1D NLTE opacity samplingmodel atmosphere code
PHOENIX to study the atmosphere ofWASP-19b. This model has been successfully used to study theatmosphere of cool stars, brown dwarfs and extrasolar planets.The temperature-pressure profile of WASP-19b computed using
PHOENIX shows the presence of thermal inversion. Our modelcomputed at solar metallicity successfully reproduces the ob-served photometry of WASP-19b without the need for non-solarcomposition. The secondary eclipse of WASP-19b shows evi-dence for CO emission features at 4.5 µ m, but however no signof H O. We find that these features are the results of thermaldissociation and thermal inversion due to the strong impingingradiation. Also, the H O pseudo-continuum is much smoother atthe concerned temperatures and densities, making it more dif-ficult to identify at those extremely coarse spectral resolutions.Our results further strengthen the fact that the family of ultra-hotJupiters commonly exhibit thermal inversions.At longer wavelengths (above 1.4 µ m) and at extremely hottemperatures (2200–2800 K), a significant amount of H O getsthermally dissociated at a pressure below 10 − bar. At a tem-perature above 2200 K, TiO and VO do remain important opac-ity sources, even at low concentrations. At longer wavelengths,CO is the only molecule with its strong triple bond to be abun-dant below 10 − bar. This molecule does not dissociate and itsemission features appear at 4.5 µ m. We suggest that the actualreason for the drop in H O in ultra-hot Jupiters is the partialthermal dissociation of this molecule and the resulting thermalinversion which shapes the thermal spectra of ultra-hot Jupiters.This makes H O a poor diagnosis of the C / O ratio. Also at suchhigh dayside temperature ( > O is spectrally much flatter and di ffi cult torecognise. Acknowledgements.
We thank the anonymous referee for providing commentsand suggestions which helped improve the clarity and conciseness of the pa-per. AR are especially grateful to Mudit Kumar Srivastava from Physical Re-search Laboratory (PRL) for providing feedback on the manuscript. The com-putations were performed on the HPC resources at the Physical Research Lab-oratory (PRL). The research leading to these results has received funding fromthe French "Programme National de Physique Stellaire" and the Programme Na-tional de Planetologie of CNRS (INSU). The computations were performed at the
Pôle Scientifique de Modélisation Numérique (PSMN) at the
École Nor-male Supérieure (ENS) in Lyon, and at the
Gesellschaft für WissenschaftlicheDatenverarbeitung Göttingen in collaboration with the Institut für AstrophysikGöttingen. O.M. acknowledges support from CNES.
References
Allard, F., Allard, N. F., Homeier, D., et al. 2007, A&A, 474, L21Allard, F., Hauschildt, P. H., Alexander, D. R., Tamanai, A., & Schweitzer, A.2001, ApJ, 556, 357Allard, F., Homeier, D., Freytag, B., et al. 2013, Memorie della Societa Astro-nomica Italiana Supplementi, 24, 128Allard, F., Homeier, D., Freytag, B., & Sharp, C. M. 2012, in EAS PublicationsSeries, Vol. 57, EAS Publications Series, ed. C. Reylé, C. Charbonnel, &M. Schultheis, 3–43Anderson, D. R., Gillon, M., Maxted, P. F. L., et al. 2010, A&A, 513, L3Anderson, D. R., Smith, A. M. S., Madhusudhan, N., et al. 2013, MNRAS, 430,3422Arcangeli, J., Désert, J.-M., Line, M. R., et al. 2018, ApJ, 855, L30Barklem, P. S., Piskunov, N., & O’Mara, B. J. 2000, A&A, 363, 1091Barman, T. 2007, ApJ, 661, L191Barman, T. S., Hauschildt, P. H., & Allard, F. 2001, ApJ, 556, 885Barman, T. S., Hauschildt, P. H., Schweitzer, A., et al. 2002, ApJ, 569, L51Bean, J. L., Désert, J.-M., Seifahrt, A., et al. 2013, ApJ, 771, 108Beatty, T. G., Madhusudhan, N., Pogge, R., et al. 2017a, AJ, 154, 242Beatty, T. G., Madhusudhan, N., Tsiaras, A., et al. 2017b, AJ, 154, 158Burrows, A., Budaj, J., & Hubeny, I. 2008, ApJ, 678, 1436Burrows, A., Sudarsky, D., & Hubeny, I. 2004, ApJ, 609, 407Burton, J. R., Watson, C. A., Littlefair, S. P., et al. 2012, ApJS, 201, 36Butler, R. P., Wright, J. T., Marcy, G. W., et al. 2006, ApJ, 646, 505Ca ff au, E., Ludwig, H.-G., Ste ff en, M., Freytag, B., & Bonifacio, P. 2011,Sol. Phys., 268, 255Charbonneau, D., Brown, T. M., Noyes, R. W., & Gilliland, R. L. 2002, ApJ,568, 377Désert, J. M., Vidal-Madjar, A., Lecavelier Des Etangs, A., et al. 2008, A&A,492, 585Diamond-Lowe, H., Stevenson, K. B., Bean, J. L., Line, M. R., & Fortney, J. J.2014, ApJ, 796, 66Evans, T. M., Sing, D. K., Kataria, T., et al. 2017, Nature, 548, 58Fortney, J. J., Lodders, K., Marley, M. S., & Freedman, R. S. 2008, ApJ, 678,1419Fortney, J. J., Sudarsky, D., Hubeny, I., et al. 2003, ApJ, 589, 615Gibson, N. P., Aigrain, S., Pollacco, D. L., et al. 2010, MNRAS, 404, L114Graven, W. M. & Long, F. J. 1954, Journal of the American Chemical Society,76, 2602Haynes, K., Mandell, A. M., Madhusudhan, N., Deming, D., & Knutson, H.2015, ApJ, 806, 146Hebb, L., Collier-Cameron, A., Triaud, A. H. M. J., et al. 2010, ApJ, 708, 224Hellier, C., Anderson, D. R., Collier-Cameron, A., et al. 2011, ApJ, 730, L31Kitzmann, D., Heng, K., Rimmer, P. B., et al. 2018, ApJ, 863, 183Knutson, H. A., Howard, A. W., & Isaacson, H. 2010, ApJ, 720, 1569Kreidberg, L., Line, M. R., Parmentier, V., et al. 2018, AJ, 156, 17Lendl, M., Gillon, M., Queloz, D., et al. 2013, A&A, 552, A2Line, M. R. & Parmentier, V. 2016, ApJ, 820, 78Line, M. R., Wolf, A. S., Zhang, X., et al. 2013, ApJ, 775, 137Lothringer, J. D., Barman, T., & Koskinen, T. 2018, ApJ, 866, 27Madhusudhan, N. 2012, ApJ, 758, 36Madhusudhan, N., Knutson, H., Fortney, J. J., & Barman, T. 2014, in Protostarsand Planets VI, ed. H. Beuther, R. S. Klessen, C. P. Dullemond, & T. Henning,739Madhusudhan, N. & Seager, S. 2009, ApJ, 707, 24Mansfield, M., Bean, J. L., Line, M. R., et al. 2018, AJ, 156, 10Nugroho, S. K., Kawahara, H., Masuda, K., et al. 2017, AJ, 154, 221Parmentier, V., Fortney, J. J., Showman, A. P., Morley, C., & Marley, M. S. 2016,ApJ, 828, 22Parmentier, V., Line, M. R., Bean, J. L., et al. 2018, A&A, 617, A110Parmentier, V., Showman, A. P., & Lian, Y. 2013, A&A, 558, A91Rajpurohit, A. S., Reylé, C., Allard, F., et al. 2013, A&A, 556, A15Rajpurohit, A. S., Reylé, C., Schultheis, M., et al. 2012, A&A, 545, A85Sedaghati, E., Bo ffi n, H. M. J., MacDonald, R. J., et al. 2017, Nature, 549, 238Sheppard, K. B., Mandell, A. M., Tamburo, P., et al. 2017, ApJ, 850, L32Southworth, J., Wheatley, P. J., & Sams, G. 2007, MNRAS, 379, L11Spiegel, D. S., Silverio, K., & Burrows, A. 2009, ApJ, 699, 1487Stevenson, K. B., Bean, J. L., Madhusudhan, N., & Harrington, J. 2014, ApJ,791, 36Swain, M., Deroo, P., Tinetti, G., et al. 2013, Icarus, 225, 432Tinetti, G., Vidal-Madjar, A., Liang, M.-C., et al. 2007, Nature, 448, 169Torres, G., Fischer, D. A., Sozzetti, A., et al. 2012, ApJ, 757, 161Unsold, A. 1968, Physik der Sternatmospharen, MIT besonder Berucksichtigungder SonneValenti, J. A. & Piskunov, N. 1996, A&AS, 118, 595Visscher, C., Moses, J. I., & Saslow, S. A. 2010, Icarus, 209, 602Zellem, R. T., Swain, M. R., Roudier, G., et al. 2017, ApJ, 844, 27n, H. M. J., MacDonald, R. J., et al. 2017, Nature, 549, 238Sheppard, K. B., Mandell, A. M., Tamburo, P., et al. 2017, ApJ, 850, L32Southworth, J., Wheatley, P. J., & Sams, G. 2007, MNRAS, 379, L11Spiegel, D. S., Silverio, K., & Burrows, A. 2009, ApJ, 699, 1487Stevenson, K. B., Bean, J. L., Madhusudhan, N., & Harrington, J. 2014, ApJ,791, 36Swain, M., Deroo, P., Tinetti, G., et al. 2013, Icarus, 225, 432Tinetti, G., Vidal-Madjar, A., Liang, M.-C., et al. 2007, Nature, 448, 169Torres, G., Fischer, D. A., Sozzetti, A., et al. 2012, ApJ, 757, 161Unsold, A. 1968, Physik der Sternatmospharen, MIT besonder Berucksichtigungder SonneValenti, J. A. & Piskunov, N. 1996, A&AS, 118, 595Visscher, C., Moses, J. I., & Saslow, S. A. 2010, Icarus, 209, 602Zellem, R. T., Swain, M. R., Roudier, G., et al. 2017, ApJ, 844, 27