Colour-magnitude diagrams of transiting exoplanets

Dransfield, Georgina ORCID: 0000-0002-3937-630X (2020). Colour-magnitude diagrams of transiting exoplanets. University of Birmingham. M.Sc.

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Abstract

Colour-Magnitude Diagrams provide a simple way of comparing populations of similar objects; and when well populated with precise measurements they allow quick inferences to be made about the bulk properties of an astronomic object simply from its proximity on a diagram to other objects. We present here a Python toolkit which allows a user to produce colour-magnitude diagrams of transiting exoplanets, comparing planets to populations of ultra-cool dwarfs and directly imaged exoplanets, to models of planetary atmospheres, and to other transiting exoplanets. Using a selection of near- and mid-infrared colour-magnitude diagrams, we show how outliers can be identified for further investigation, and how emerging sub-populations can be identified. Additionally, we present evidence that observed differences in the Spitzer’s 4.5\(\mu\)m flux, between irradiated Jupiters, and field field brown dwarfs, might be attributed to Phosphine, which is susceptible to photolysis. If confirmed, this may negate the need for thermal inversions to explain eclipse measurements. We extend this reasoning to other objects and speculate that the anomalously low 4.5\(\mu\)m flux flux of the nightside of HD189733b and the daysides of GJ 436b and GJ 3470b might be caused by Phosphine absorption. Finally, we use our toolkit to include Hubble WFC3 spectra, creating a new photometric band called the ‘Water band’ (W\(_{JH}\)-band) in the process. We show that the colour index [W\(_{JH}\)-H] can be used to constrain the C/O ratio of exoplanets, showing that future observations with JWST and ARIEL will be able to distinguish these populations if they exist, and select members for future follow-up.
The work presented in this thesis is being prepared for publication in a paper on which I will be first author. The abstract above is lifted verbatim from the current manuscript of that paper.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):