V1298 Tau: The story of warm gas giants orbiting an adolescent star

We are presenting the first atmospheric study of a young transiting exoplanet. We focus on the V1298 Tau system, which contains 4 giant transiting planets that orbit the young (23Myr) T Tauri star V1298 Tau. We have observed one primary transit of planet V1298 Tau b with HST to learn about its atmospheric properties. This planet is ideally suited for atmospheric studies using transmission spectroscopy since it is a warm gas giant (Teq=677 K) with a very large atmospheric scale height (~250 km).From theoretical models we expect strong water absorption features in its transmission spectra. However, this planet is particularly interesting since it is expected to be undergoing atmospheric 'erosion' due to high XUV flux from its host star and its internal heat of formation, and show how our observations can constrained the escape rate. The V1298 Tau system is also interesting for the study of comparative exoplanetology between four freshly formed planets as their atmospheres are expected to carry fossil signatures of the planetary disk from which they formed. As a follow-up of the HST observations, we are scheduling observations planets b and c with JWST+NIRSpec in transmission as part of a GO-1 accepted proposal. V1298 Tau is an active star and we find signatures of bright spots and flares on the stellar surface with the HST+WFC3 observations, and emphasise the challenges that the stellar activity poses for such system. In this poster, we present results from the current programs and highlight the scientific interests of this system.