KELT-11 b: Abundances of Water and Constraints on Carbon-bearing Molecules from the Hubble Transmission Spectrum

Abstract

In the past decade, the analysis of exoplanet atmospheric spectra has revealed the presence of water vapor in almost all the planets observed, with the exception of a fraction of overcast planets. Indeed, water vapor presents a large absorption signature in the wavelength coverage of the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3), which is the main space-based observatory for atmospheric studies of exoplanets, making its detection very robust. However, while carbon-bearing species such as methane, carbon monoxide, and carbon dioxide are also predicted from current chemical models, their direct detection and abundance characterization has remained a challenge. Here we analyze the transmission spectrum of the puffy, clear hot-Jupiter KELT-11 b from the HST WFC3 camera. We find that the spectrum is consistent with the presence of water vapor and an additional absorption at longer wavelengths than 1.5 μm, which could well be explained by a mix of carbon bearing molecules. CO 2 , when included is systematically detected. One of the main difficulties to constrain the abundance of those molecules is their weak signatures across the HST WFC3 wavelength coverage, particularly when compared to those of water. Through a comprehensive retrieval analysis, we attempt to explain the main degeneracies present in this data set and explore some of the recurrent challenges that are occurring in retrieval studies (e.g., the impact of model selection, the use of free versus self-consistent chemistry, and the combination of instrument observations). Our results make this planet an exceptional example of a chemical laboratory to test current physical and chemical models of the atmospheres of hot Jupiters.

ARES.* V. No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b

“…While it has become common to combine data from different instruments, there may be an offset between the data sets. These offsets can occur owing to imperfect correction of instrument systematics, from the use of different orbital parameters or limbdarkening coefficients during the light-curve fitting, or from stellar variability or activity (e.g., Stevenson et al 2014aStevenson et al , 2014bMorello et al 2017;Tsiaras et al 2018;Bruno et al 2020;Yip et al 2020Yip et al , 2021Changeat et al 2020;Murgas et al 2020;Pluriel et al 2020;Schlawin et al 2021). As there is no wavelength overlap between our HST observations and the Note.…”

Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b

“…We note that the compatibility of different data sets is hard to confirm, particularly without spectral overlap, as the use of different limb-darkening coefficients or orbital parameters, imperfect correction of instrument systematics, or stellar activity and stellar variability can all cause variations in the transit depth observed (e.g., Tsiaras et al 2018;Alexoudi et al 2018;Yip et al 2020aYip et al , 2020bChangeat et al 2020;Pluriel et al 2020) 2019), but used logarithmic limb-darkening coefficients. However, the TESS depth recovered here matches well with the ground-based data and was derived using the four-coefficient law from Claret (2017).…”

A comparison of chemical models of exoplanet atmospheres enabled by TauREx 3.1

“…Current data are often sparse and with low signal to noise, leading to degeneracies that require the use of sophisticated modelling tools to be interpreted correctly. Despite these limitations, the atmospheres of large ultra hot-Jupiters (Haynes et al 2015;Mikal-Evans et al 2019;Edwards et al 2020;Mikal-Evans et al 2020;Gandhi et al 2020;Changeat & Edwards 2021a), hot-Jupiters (Tinetti et al 2007;Swain et al 2008Swain et al , 2009bLine et al 2014;Stevenson et al 2014Stevenson et al , 2017MacDonald & Madhusudhan 2017;Changeat et al 2020b;Pluriel et al 2020;Changeat et al 2021) and hot-Saturn (Nikolov et al 2018;Skaf et al 2020;Anisman et al 2020;Yip et al 2021) are regularly characterised using the transit, eclipse and phase-curve techniques. Smaller transitional planets are notoriously more challenging, but the Hubble Space Telescope has allowed us to infer some constraints for a few of these worlds (Kreidberg et al 2014;de Wit et al 2016;Tsiaras et al 2016;de Wit et al 2018;Tsiaras et al 2019;Benneke et al 2019;Madhusudhan et al 2020;Guilluy et al 2021;Edwards et al 2021;Mugnai et al 2021;Swain et al 2021).…”