Retrieval study of cool, directly imaged exoplanet 51 Eri b
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Retrieval methods are a powerful analysis technique for modelling exoplanetary atmospheres by estimating the bulk physical and chemical properties that combine in a forward model to best-fit an observed spectrum, and they are increasingly being applied to observations of directly-imaged exoplanets. We have adapted TauREx3, the Bayesian retrieval suite, for the analysis of near-infrared spectrophotometry from directly-imaged gas giant exoplanets and brown dwarfs. We demonstrate TauREx3’s applicability to sub-stellar atmospheres by presenting results for brown dwarf benchmark GJ 570D which are consistent with previous retrieval studies, whilst also exhibiting systematic biases associated with the presence of alkali lines. We also present results for the cool exoplanet 51 Eri b, the first application of a free chemistry retrieval analysis to this object, using spectroscopic observations from GPI and SPHERE. While our retrieval analysis is able to explain spectroscopic and photometric observations without employing cloud extinction, we conclude this may be a result of employing a flexible temperature-pressure profile which is able to mimic the presence of clouds. We present Bayesian evidence for an ammonia detection with a 2.7σ confidence, the first indication of ammonia in an exoplanetary atmosphere. This is consistent with this molecule being present in brown dwarfs of a similar spectral type. We demonstrate the chemical similarities between 51 Eri b and GJ 570D in relation to their retrieved molecular abundances. Finally, we show that overall retrieval conclusions for 51 Eri b can vary when employing different spectral data and modelling components, such as temperature-pressure and cloud structures.
Whiteford , N , Glasse , A , Chubb , K L , Kitzmann , D , Ray , S , Phillips , M W , Biller , B A , Palmer , P I , Rice , K , Waldmann , I P , Changeat , Q , Skaf , N , Wang , J , Edwards , B & Al-Refaie , A 2023 , ' Retrieval study of cool, directly imaged exoplanet 51 Eri b ' , Monthly Notices of the Royal Astronomical Society , vol. 525 , no. 1 , stad670 , pp. 1375-1400 . https://doi.org/10.1093/mnras/stad670
Monthly Notices of the Royal Astronomical Society
Copyright © 2023 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the final published version of the work, which was originally published at https://doi.org/10.1093/mnras/stad670.
DescriptionFunding: NW acknowledgements postgraduate funding from the UK’s Science and Technology Facilities Council (STFC), NSF Award 1909776 and NASA Award 80NSSC22K0142. IW acknowledgements funding from the UK’s Science and Technology Facilities Council (STFC) and from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 758892, ExoAI). Furthermore, IW acknowledges funding by the Science and Technology Funding Council (STFC) grants: ST/K502406/1, ST/P000282/1, ST/P002153/1 and ST/S002634/1. NS acknowledges funding from the OCAVPSL project.
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