Disequilibrium Chemistry in Exoplanet Atmospheres Observed with the Hubble Space Telescope

Roudier, G.; Swain, Mark R.; Gudipati, Murthy S.; West, Robert A.; Estrela, Raissa; Zellem, Robert T.

doi:10.3847/1538-3881/abfdad

Cited by 37 publications

(37 citation statements)

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“…Since the last two groups return similar results, we choose to calculate A H using reduced data from Mugnai et al (2021), which is also close to the A H calculated from Libby-Roberts et al (2021). A trend study using uniform data reduction methods would be preferred, allowing for more rigorous comparison between exoplanets intrinsic properties (e.g., Sing et al 2016;Tsiaras et al 2018;Roudier et al 2021). At present, we choose reduced data from the more recently published works, which either incorporate data from more recent transit observations (e.g., HD 97658 b we use Guo et al 2020instead of Knutson et al 2014a or use more up-to-date stellar parameters (e.g., K2-18b we use Benneke et al 2019ainstead of Tsiaras et al 2019.…”

Section: Transmission Data Reductionmentioning

confidence: 99%

Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets

Dymont,

Yu,

Ohno

et al. 2021

Preprint

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Relatively little is understood about the atmospheric composition of temperate to warm exoplanets (equilibrium temperature T eq < 1000 K), as many of them are found to have uncharacteristically flat transmission spectra. Their flattened spectra are likely due to atmospheric opacity sources such as planet-wide photochemical hazes and condensation clouds. We compile the transmission spectra of 23 warm exoplanets previously observed by the Hubble Space Telescope and quantify the haziness of each exoplanet using a normalized amplitude of the water absorption feature (A H ). By examining the relationships between A H and various planetary and stellar forcing parameters, we endeavor to find correlations of haziness associated with planetary properties. Our analysis shows that the previously identified linear trends between A H and T eq or hydrogen-helium envelope mass fraction (f HHe ) break down with the addition of new exoplanet data. Among all the parameters we investigated, atmospheric scale height (H), planet gravity (g p ), and planet density (ρ p ) hold the most statistically significant linear or linear logrithmic correlations with A H (p ≤ 0.02). We also tentatively identified positive correlations for eccentricity (e) and stellar age (t age ) with A H . Specifically, lower H, higher g p , ρ p , e, or t age lead to clearer atmospheres. However, none of the parameters show very strong linear correlations with A H , suggesting that haziness in warm exoplanets is not simply controlled by any single planetary/stellar parameter. Additional observations and laboratory experiments are needed to fully understand the complex physical and chemical processes that lead to the hazy/cloudy atmospheres in warm exoplanets.

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Section: Transmission Data Reductionmentioning

confidence: 99%

Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets

Dymont,

Yu,

Ohno

et al. 2021

Preprint

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“…Detection of clouds and hazes is typically done through measuring the degree of spectral modulation (Sing et al 2016), which can then be compared to estimates of the theoretical possible values (Iyer et al 2016;Gao et al 2020) or plotted against various physical parameters to search for correlations (Stevenson 2016;Fu et al 2017;Gao et al 2020;Dymont et al 2021). Here, we perform this analysis using the catalog from Roudier et al (2021) that consists of 62 planets observed with the WFC3 instrument onboard the HST using the G141 infrared (IR) grism (1.1-1.6 µm) spatial scan observations. Compared with previous works, this exoplanet catalog has three important advantages for the study of clouds.…”

Section: Methodsmentioning

confidence: 99%

A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres

Estrela¹,

Swain²,

Roudier³

2022

Preprint

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The transmission spectra of exoplanet atmospheres observed with the Hubble Space Telescope in the near-infrared range (1.1-1.65µm) frequently show evidence for some combination of clouds and hazes. Identification of systematic trends in exoplanet clouds and hazes is potentially important for understanding atmospheric composition and temperature structure. Here we report on the analysis of spectral modulation using the largest uniformly processed sample of exoplanet transit spectra currently available. The spectral retrieval includes the capability to detect and represent atmospheres in which the composition departs from thermochemical equilibrium. Using this catalog, we find that the impact of clouds/hazes, measured in terms of damping of spectral features, follows a trend from mostly cloudy/hazy around 500 K to mostly clear around 1650 K. For planets at lower temperatures (< 270 K), we observe a potential rise towards reduced cloudy/hazy atmospheres. We also find that a partially transparent aerosol component is frequently present and that it is typically vertically distributed throughout the atmospheric column. Our findings also suggest that while clouds and hazes are common in exoplanet atmospheres, the majority of planets have detectable spectral modulation that is sufficient for characterizing their atmospheres. Additionally, the empirical trend that clouds and hazes are minimized at 1650 +874 −620 K revealed in our catalog has predictive utility for modelling the performance of large-scale transiting exoplanets survey, such as planned with the Ariel mission. This trend can also be used for making a probability-based forecast of spectral modulation for a given source in the context of future JWST observations.

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“…A key motivation for a robust IM is the application to comparative planetology, and this IM can provide uniform estimation of spectrum across a large number of targets. A large scale analysis using the same IM and estimation methodology presented in this paper is performed in Roudier et al (2021). Analyses like this referenced one, can benefit from applying the IM analysis techniques employed in this paper, and specific metrics such as RSDSN can be used to flag targets in the set that might not conform to the IM assumptions.…”

Section: Application To Comparative Planetologymentioning

confidence: 99%

Characterization of an Instrument Model for Exoplanet Transit Spectrum Estimation through Wide Scale Analysis on HST Data

Huber-Feely,

Swain,

Roudier

et al. 2021

Preprint

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Instrument models (IMs) enable the reduction of systematic error in transit spectroscopy light curve data, but, since the model formulation can influence the estimation of science model parameters, characterization of the instrument model effects is crucial to the interpretation of the reduced data. We analyze a simple instrument model and assess its validity and performance across Hubble WFC3 and STIS instruments. Over a large, n = 63, sample of observed targets, an MCMC sampler computes the parent distribution of each instrument model parameter. Possible parent distribution functions are then fit and tested against the empirical IM distribution. Correlation and other analyses are then performed to find IM relationships. The model is shown to perform well across the 2 instruments and 3 filters analyzed and, further, the Student's t-distribution is shown to closely fit the empirical parent distribution of IM parameters and the Gaussian is shown to poorly model the observed distribution. This parent distribution can be used in the MCMC prior fitting and demonstrates IM consistency for wide scale atmospheric analysis using this model. Finally, we propose a simple metric based on light curve residuals to determine model performance, and we demonstrate its ability to determine whether a derived spectrum under this IM is high quality and robust.

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Disequilibrium Chemistry in Exoplanet Atmospheres Observed with the Hubble Space Telescope

Cited by 37 publications

References 50 publications

Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets

Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets

A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres

Characterization of an Instrument Model for Exoplanet Transit Spectrum Estimation through Wide Scale Analysis on HST Data

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