Atmospheric characterization of exoplanets around active host stars

• Applicant: Privatdozentin Sara Khalafinejad, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 446657087

We are living in the exciting era of discovery and characterization of extra-solar planets. The number of discovered planets increases almost on a daily basis, and currently exceeds 4000. Characterization of exoplanetary atmospheres is a crucial step in order to predict and investigate the right conditions for life to emerge on a planet. It also provides pivotal information to potentially link the planet composition to its formation pathway and evolution. Transmission spectroscopy is one of the most powerful techniques for constraining the chemical composition and the physical parameters of the exoplanetary atmospheres.However, given the currently known exoplanet population, observing facilities and analysis techniques, only the atmospheres of a handful of them have proven suitable for an in-depth investigation. An important hindrance is the effect of the host star on the detectability of the atmospheric spectral signatures; namely stellar activity (e.g., spots and faculae) and stellar effects related to the geometry (e.g., differential limb-darkening and Rossiter-McLaughlin, RM-effect). Hence, it is crucial to develop novel techniques to efficiently account for these effects, before revolutionary facilities such as JWST, the ELT and Plato become available.I propose to combine simultaneous low- and high-resolution transit spectroscopy as well as transit photometry. These are sensitive to complementary information, and can be used together to cover each of their individual shortcomings. Using this technique, I will: 1) develop a framework to disentangle the stellar nuisance effects from the exoplanetary atmospheric transmitted signals, and 2) obtain a full picture from lower to upper atmosphere and tease out tight constraints on the atmospheric physical properties such as number densities of species and cloud-layer altitudes. Ultimately, after characterization of a sample of planet candidates, I intend to perform a comparative study to further understand the planetary atmospheric evolution and diversity.I will start by analyzing observations of multiple hot Jupiters, which are already available to me at present. Then, I will develop a joint analysis technique, by merging the tools that my collaborators and I have already developed for consideration of stellar flares, large spots, stellar photospheric temperature heterogeneity, stellar differential limb-darkening and RM-effect. The final stage in the production of my framework is to use the planetary atmospheric modelling tools e.g., petitRADTRANS, to jointly constrain the physical properties of exoplanetary atmospheres, enabling comparative exo-planetology across a wide sample using uniform methods.This technique will be available for the community as a powerful tool for future applications to the characterization of low-mass exoplanets around M-dwarfs (which typically show higher a level of activity), as well as the targets which will be discovered by TESS, CHEOPS and JWST in the near future.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1992: Exploring the diversity of extrasolar planets