Chloe Fisher

PhD Student at the University of Bern
working on Exoplanet Atmospheres.

Recent Projects

Non-LTE vs LTE Sodium doublet

Non-LTE Analysis of Sodium

We investigated the effects of dropping the LTE assumption for sodium on high- and low-res data, and explored the differences in the atmospheric retrieval results.

Feature Importances for random forest prediction on different parameters

Supervised Machine Learning for Atmospheric Retrieval

I am working on developing an atmospheric retrieval code using machine learning. We are currently using "Random Forests" to analyse spectra and inform us about the chemical composition, temperature and clouds in the planet's atmosphere.

H2O abundance vs Mass retrieval results

Retrieval Analysis of WFC3 Data

We studied a population of planets with WFC3 data to look for trends in their properties and investigate issues with the current techniques used to examine transmission spectra.


I am working on developing atmospheric retrieval methods involving machine learning techniques for extrasolar planets. I also work on different aspects of the theory of transimission spectra, and analysing traditional methods of retrieval.

Chloe giving an outreach talk at Pint of Science Bern 2019

First Author Papers

Fisher, C., & Heng, K. 2019, ApJ,
How much information does the sodium doublet encode? Retrieval analysis of Non-LTE sodium lines at low and high spectral resolutions

Fisher, C., & Heng, K. 2018, MNRAS, 481, 4698
Retrieval analysis of 38 WFC3 transmission spectra and resolution of the normalization degeneracy

Other Papers

Hoeijmakers, H. J., et al. 2019, A&A,
A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9b

Seidel, J. V., et al. 2019, A&A,
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) - II. A broadened sodium feature on the ultra-hot giant WASP-76b

Márquez-Neila, P., Fisher, C., Sznitman, R., & Heng, K. 2018, Nature Astronomy, 2, 719
Supervised machine learning for analysing spectra of exoplanetary atmospheres


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Our random forest retrieval code HELA, along with all the Exoclimes Simulation Platform open-source codes, can be found on our github page.

About Me

I am a PhD student at the University of Bern in Switzerland. I am working in Professor Kevin Heng's group at the Centre for Space and Habitability. We study the atmospheres of extrasolar planets to try to determine their composition and climate. Born in the UK, I did my undergraduate degree in mathematics at the University of Cambridge, followed by a master's in Astrophysics. In August, 2017 I joined Kevin's group in Bern.

Chloe skiing in the Adelboden/Lenk region


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University of Bern
Centre for Space and Habitability (CSH)

Gesellschaftsstrasse 6 (G6)
3012 Bern