Abstract

Colour-Magnitude diagrams form a traditional way of representing luminous objects in the Universe and compare them to each others. We can measure the flux emitted by a planet's dayside when it undergoes an occultation. Combining this flux with a distance measurement, the absolute magnitude of that planet can be estimated. Colour-magnitude diagrams are composed in the near and mid infra-red for 44 transiting extrasolar planets. When possible, planets are plotted alongside very low-mass stars and field brown dwarfs, who often share similar sizes and equilibrium temperatures. They offer a natural, empirical, comparison sample. We also include directly imaged exoplanets and the expected loci of pure blackbodies. Irradiated planets do not match blackbodies; their emission spectra are not featureless. For a given luminosity, hot Jupiters' daysides show a larger variety in colour than brown dwarfs do and display an increasing diversity in colour with decreasing intrinsic luminosity. The presence of an extra absorbent within the 4.5 micron band would reconcile most hot Jupiters with ultra-cool dwarfs' atmospheres. Measuring the emission of gas giants cooler than 1000 K would disentangle whether planets' atmospheres behave more similarly to brown dwarfs' atmospheres than to blackbodies, whether they are akin to the young directly imaged planets, or if hot Jupiters form their own sequence.

Presentation

Poster