Young planetary systems are the promising targets to constrain the models and timescales of planetary formation, migration and atmospheres. The stellar obliquity (λ) can be a probe to planet migration history, and various migration theories with different timescales differ strongly in their predictions on the obliquity. The atmosphere loss can be responsible for the currently observed “Neptunian desert”, while the general contributions of atmospheric loss, e.g., by photoevaporation, is currently unknown. Therefore, observations on young planetary systems becomes urgent. In this proposal, we plan to observe K2-100 planetary system, a young Neptune-sized planet in the Praesepe Cluster (Age: 750 Myr). We propose high resolution spectroscopy in both visible and near infrared, to observe the Rossiter-McLaughlin effect for obliquity measurement and transmission spectra for planetary atmosphere loss study. Our observation will test our predictions on the target: (1) To distinguish whether the planet is spin-orbit aligned. This could help retrieve the planet’s migration history. (2) To test if the planet is losing atmosphere. The excess absorption suggesting atmosphere escape can be seen as expected in Hα 656 nm and Helium triplet at 1083 nm.
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