Seeing above the clouds with high-resolution spectroscopy

Gandhi, Siddharth; Brogi, Matteo; Webb, Rebecca K.

doi:10.1093/mnras/staa2424

Cited by 49 publications

(43 citation statements)

References 98 publications

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“…Our results statistically favour the presence of aerosols in the atmosphere of HD 209458b (Extended Data Fig. 4), which dampen the amplitude of the molecular lines but do not evidently hamper their detection 24,25 . This supports the results of other observations of this planet (see Methods).…”

supporting

confidence: 65%

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

Giacobbe

Brogi

Gandhi

et al. 2021

Nature

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143

113

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209458b formed far from its present location and subsequently migrated inwards 11,13 . Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions.We observed four transits of HD 209458b, the archetype of transiting hot Jupiters, with the near-infrared echelle spectrograph GIANO-B 14 , mounted at the 3.6-m Telescopio Nazionale Galileo located in La Palma, Spain. The transits happened on

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supporting

confidence: 65%

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

Giacobbe

Brogi

Gandhi

et al. 2021

Nature

Self Cite

143

113

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“…Following the receipt proposed by [9], we thus converted the cross-correlation values into likelihood values, and we used the likelihood-ratio test to compare the different models. Our results statistically favour the presence of aerosols in the atmosphere of HD 209458 b which dampen the amplitude of the molecular lines but do not evidently hamper their detection [23,26]. Furthermore, the atmospheric models we tested in thermochemical equilibrium seem to prefer a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55).…”

Section: Observations and Analysis Of Giano-b High-resolution Spectrasupporting

confidence: 60%

On the synergy between Ariel and ground-based high-resolution spectroscopy

et al. 2022

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Since the first discovery of an extra-solar planet around a main-sequence star, in 1995, the number of detected exoplanets has increased enormously. Over the past two decades, observational instruments (both onboard and on ground-based facilities) have revealed an astonishing diversity in planetary physical features (i. e. mass and radius), and orbital parameters (e.g. period, semi-major axis, inclination). Exoplanetary atmospheres provide direct clues to understand the origin of these differences through their observable spectral imprints. In the near future, upcoming ground and space-based telescopes will shift the focus of exoplanetary science from an era of “species discovery” to one of “atmospheric characterization”. In this context, the Atmospheric Remote-sensing Infrared Exoplanet Large (Ariel) survey, will play a key role. As it is designed to observe and characterize a large and diverse sample of exoplanets, Ariel will provide constraints on a wide gamut of atmospheric properties allowing us to extract much more information than has been possible so far (e.g. insights into the planetary formation and evolution processes). The low resolution spectra obtained with Ariel will probe layers different from those observed by ground-based high resolution spectroscopy, therefore the synergy between these two techniques offers a unique opportunity to understanding the physics of planetary atmospheres. In this paper, we set the basis for building up a framework to effectively utilise, at near-infrared wavelengths, high-resolution datasets (analyzed via the cross-correlation technique) with spectral retrieval analyses based on Ariel low-resolution spectroscopy. We show preliminary results, using a benchmark object, namely HD 209458 b, addressing the possibility of providing improved constraints on the temperature structure and molecular/atomic abundances.

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“…Finally, complementary information on K2-18b's atmosphere could be provided by high-resolution Doppler spectroscopy from ground-based instruments. Such observations can be efficient to probe cloudy atmospheres and to constrain abundances and cloud-top pressure (Gandhi et al 2020). As shown by Blain et al (2021), one full transit of K2-18b observed with VLT-CRIRES+ might be sufficient to detect CH 4 .…”

Section: Observational Transit Spectramentioning

confidence: 95%

Formation and dynamics of water clouds on temperate sub-Neptunes: the example of K2-18b

Charnay

Blain

Bézard

et al. 2021

A&A

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Context. Hubble Space Telescope (HST) spectroscopic transit observations of the temperate sub-Neptune K2-18b were interpreted as the presence of water vapour with potential water clouds. 1D modelling studies also predict the formation of water clouds in K2-18b’s atmosphere in some conditions. However, such models cannot predict the cloud cover, which is driven by atmospheric dynamics and thermal contrasts, and thus neither can they predict the real impact of clouds on spectra. Aims. The main goal of this study is to understand the formation, distribution, and observational consequences of water clouds on K2-18b and other temperate sub-Neptunes. Methods. We simulated the atmospheric dynamics, water cloud formation, and spectra of K2-18b for a H2-dominated atmosphere using a 3D general circulation model. We analysed the impact of atmospheric composition (with metallicity from 1× solar to 1000× solar), concentration of cloud condensation nuclei, and planetary rotation rate. Results. Assuming that K2-18b has a synchronous rotation, we show that the atmospheric circulation in the upper atmosphere essentially corresponds to a symmetric day-to-night circulation with very efficient heat redistribution. This regime preferentially leads to cloud formation at the sub-stellar point or at the terminator. Clouds form at metallicity ≥100× solar with relatively large particles (radius = 30–450 μm). At 100–300× solar metallicity, the cloud fraction at the terminators is small with a limited impact on transit spectra. At 1000× solar metallicity, very thick clouds form at the terminator, greatly flattening the transit spectrum. The cloud distribution appears very sensitive to the concentration of cloud condensation nuclei and to the planetary rotation rate, although the impact on transit spectra is modest in the near-infrared. Fitting HST transit data with our simulated spectra suggests a metallicity of ~100–300× solar, which is consistent with the mass-metallicity trend of giant planets in the Solar System. In addition, we found that the cloud fraction at the terminator can be highly variable in some conditions, leading to a potential variability in transit spectra that is correlated with spectral windows. This effect could be common on cloudy exoplanets and could be detectable with multiple transit observations. Finally, the complex cloud dynamics revealed in this study highlight the inherent 3D nature of clouds shaped by couplings between microphysics, radiation, and atmospheric circulation.

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Seeing above the clouds with high-resolution spectroscopy

Cited by 49 publications

References 98 publications

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

On the synergy between Ariel and ground-based high-resolution spectroscopy

Formation and dynamics of water clouds on temperate sub-Neptunes: the example of K2-18b

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