Optical phase curves as diagnostics for aerosol composition in exoplanetary atmospheres

Oreshenko, Maria; Heng, Kevin; Demory, Brice-Olivier

doi:10.1093/mnras/stw133

Cited by 77 publications

(64 citation statements)

References 50 publications

(109 reference statements)

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“…One example of this is supersolar metallicities, which have been shown to increase the day-night temperature difference in GCMs (e.g., Showman et al 2009;Kataria et al 2015;Wong et al 2016). Another possibility is highaltitude clouds, which are expected to form largely on the nightside and western limb (Lee et al 2016;Oreshenko et al 2016;Parmentier et al 2016), where it is coldest. As a result, clouds could increase the amplitude of the phase curve and thereby raise our theoretical predictions for A closer to observed values.…”

mentioning

confidence: 99%

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Komacek

Showman

Tan

2017

ApJ

147

183

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The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing fractional daysidenightside brightness temperature difference with increasing incident stellar flux, both averaged across the infrared and in each individual wavelength band. The analytic theory of Komacek & Showman shows that this trend is due to the decreasing ability with increasing incident stellar flux of waves to propagate from day to night and erase temperature differences. Here, we compare the predictions of this theory with observations, showing that it explains well the shape of the trend of increasing dayside-nightside temperature difference with increasing equilibrium temperature. Applied to individual planets, the theory matches well with observations at high equilibrium temperatures but, for a fixed photosphere pressure of 100 mbar, systematically underpredicts the dayside-nightside brightness temperature differences at equilibrium temperatures less than 2000 K. We interpret this as being due to the effects of a process that moves the infrared photospheres of these cooler hot Jupiters to lower pressures. We also utilize general circulation modeling with double-gray radiative transfer to explore how the circulation changes with equilibrium temperature and drag strengths. As expected from our theory, the dayside-nightside temperature differences from our numerical simulations increase with increasing incident stellar flux and drag strengths. We calculate model phase curves using our general circulation models, from which we compare the broadband infrared offset from the substellar point and dayside-nightside brightness temperature differences against observations, finding that strong drag or additional effects (e.g., clouds and/or supersolar metallicities) are necessary to explain many observed phase curves.

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mentioning

confidence: 99%

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Komacek

Showman

Tan

2017

ApJ

147

183

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“…Kepler-43b was removed from the analysis as it is doubtful whether the signal is of planetary origin or due to stellar activity (Esteves et al 2015). specific to each cloud species to calculate the phase curves andcompare our models to all known shifted Kepler light curves, whereas these authors focused on Kepler-7b. As a result, we are able to draw conclusions that Oreshenko et al (2016) could not, within their study.…”

Section: Introductionmentioning

confidence: 74%

“…Unlike previous work Hu et al 2015;Munoz & Isaak 2015;Shporer & Hu 2015;Webber et al 2015) that aimed to fit ad hoc cloud models to the Kepler light curves by treating the condensation curve of the cloud, the thermal structure of the planet, or the optical properties of the clouds as free parameters, we calculate a priori the 3D thermal structure and use the condensation temperature and cloud optical properties from known potential condensates to constrain the cloud physical properties and composition. Our work is also different from Oreshenko et al (2016), who also compared the temperature map from a global circulation model to the condensation curve of different cloud species. We aimfor a more detailed calculation of observable signaturesand a much wider comparison to observations.…”

Section: Introductionmentioning

confidence: 90%

Transitions in the Cloud Composition of Hot Jupiters

Parmentier

Fortney

Showman

et al. 2016

ApJ

309

436

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Over a large range of equilibrium temperatures, clouds shape the transmission spectrum of hot Jupiter atmospheres, yet their composition remains unknown. Recent observations show that the Kepler lightcurves of some hot Jupiters are asymmetric: for the hottest planets, the lightcurve peaks before secondary eclipse, whereas for planets cooler than ∼1900 K, it peaks after secondary eclipse. We use the thermal structure from 3D global circulation models to determine the expected cloud distribution and Kepler lightcurves of hot Jupiters. We demonstrate that the change from an optical lightcurve dominated by thermal emission to one dominated by scattering (reflection) naturally explains the observed trend from negative to positive offset. For the cool planets the presence of an asymmetry in the Kepler light curve is a telltale sign of the cloud composition, because each cloud species can produce an offset only over a narrow range of effective temperatures. By comparing our models and the observations, we show that the cloud composition of hot Jupiters likely varies with equilibrium temperature. We suggest that a transition occurs between silicate and manganese sulfide clouds at a temperature near 1600 K, analogous to the L/T transition on brown dwarfs. The cold trapping of cloud species below the photosphere naturally produces such a transition and predicts similar transitions for other condensates, including TiO. We predict that most hot Jupiters should have cloudy nightsides, that partial cloudiness should be common at the limb, and that the dayside hot spot should often be cloud-free.

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“…Specifically, the phase offset between secondary eclipse and when the peak planet flux is observed oscillates between times before and after secondary eclipse. This has been interpreted as reflected light variations due to time-variable cloud coverage on the dayside (Oreshenko et al 2016;Parmentier et al 2016a;Helling & Rimmer 2019). However, our Figure 21 shows that the dayside opacity is overwhelmed by gas-phase contributions and that high-temperature cloud species formed on the dayside are likely not responsible for the phase curve observations.…”

Section: Preeminent Opacity Sources: P Gas (τ(λ) = 1)mentioning

confidence: 99%

Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b

Helling

Iro

Corrales

et al. 2019

A&A

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Context. Of the presently known ≈ 3900 exoplanets, sparse spectral observations are available for ≈ 100. Ultra-hot Jupiters have recently attracted interest from observers and theoreticians alike, as they provide observationally accessible test cases. Aims. We aim to study cloud formation on the ultra-hot Jupiter HAT-P-7b, the resulting composition of the local gas phase, and how their global changes affect wavelength-dependent observations utilised to derive fundamental properties of the planet. Methods. We apply a hierarchical modelling approach as a virtual laboratory to study cloud formation and gas-phase chemistry. We utilise 97 vertical 1D profiles of a 3D GCM for HAT-P-7b to evaluate our kinetic cloud formation model consistently with the local equilibrium gas-phase composition. We use maps and slice views to provide a global understanding of the cloud and gas chemistry. Results. The day/night temperature difference on HAT-P-7b (∆T ≈ 2500 K) causes clouds to form on the nightside (dominated by H 2 /He) while the dayside (dominated by H/He) retains cloud-free equatorial regions. The cloud particles vary in composition and size throughout the vertical extension of the cloud, but also globally. TiO 2 [s]/Al 2 O 3 [s]/CaTiO 3 [s]-particles of cm-sized radii occur in the higher dayside-latitudes, resulting in a dayside dominated by gas-phase opacity. The opacity on the nightside, however, is dominated by 0.01 . . . 0.1 µm particles made of a material mix dominated by silicates. The gas pressure at which the atmosphere becomes optically thick is ∼ 10 −4 bar in cloudy regions, and ∼ 0.1 bar in cloud-free regions. Conclusions. HAT-P-7b features strong morning/evening terminator asymmetries, providing an example of patchy clouds and azimuthally-inhomogeneous chemistry. Variable terminator properties may be accessible by ingress/egress transmission photometry (e.g., CHEOPS and PLATO) or spectroscopy. The large temperature differences of ≈2500 K result in an increasing geometrical extension from the night-to the dayside. The chemcial equilibrium H 2 O abundance at the terminator changes by < 1 dex with altitude and 0.3 dex (a factor of 2) across the terminator for a given pressure, indicating that H 2 O abundances derived from transmission spectra can be representative of the well-mixed metallicity at P 10 bar. We suggest the atmospheric C/O as an important tool to trace the presence and location of clouds in exoplanet atmospheres. The atmospheric C/O can be sub-and supersolar due to cloud formation. Phase curve variability of HAT-P-7b is unlikely to be caused by dayside clouds.

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Optical phase curves as diagnostics for aerosol composition in exoplanetary atmospheres

Cited by 77 publications

References 50 publications

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Transitions in the Cloud Composition of Hot Jupiters

Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b

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