Yifan Zhou (UoA)

Cloud Atlas: Characterizing Directly-Imaged Exoplanets with Time-Resolved Observations // Directly-imaged exoplanets and planetary-mass companions form a valuable sample for exoplanetary atmospheric studies. They are among the best-characterized exoplanets because of the availability of direct spectroscopic observations. However, the disagreement between the models and the observations also raise crucial questions primarily concerning the condensate clouds in their atmospheres. Condensate clouds, which cannot be well constrained by time-integrated spectroscopy, contribute the largest uncertainty in characterizing ultra-cool atmospheres of exoplanets. Time-resolved observations that monitor the brightness and spectral variabilities induced by heterogeneous atmospheres have achieved great success in studying the cloud structures of brown dwarfs. These observations will be particularly powerful when applied to high-contrast directly-imaged planets. In Cloud Atlas, an HST Large Treasury program, we use time-resolved precision photometry and spectroscopy to study different cloud structures in brown dwarfs and planetary mass companions. In this talk, I will present the latest HST/WFC3 near-infrared light curves of directly-imaged planetary-mass companions and address both the observational techniques and the scientific implications. By placing the multi-wavelength modulation amplitude measurements of planetary-mass companions into the context of brown dwarfs, I will discuss the cloud properties in intermediate- and low-surface gravity atmospheres. I will also explore the angular momentum evolution of planetary-mass companions based on rotational period measurements. With the development of high-contrast imaging instruments in the near future, time-resolved observations will be even more effective in characterizing directly-imaged exoplanets.