Searching for Escaping Metals from 2 Young (< 30 Myr) Neptune-sized Planets

Photoevaporation, the removal of a planet’s atmosphere via high-energy irradiation, is predicted to affect planets < 100 Myr, when the host star is still active. Observing atmospheric escape for young planets is challenging given that hydrogen (Hα, Lymanα) and helium (e.g. He 10830 Angstroms) are variable in the star. Here, we present Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) transit observations of AU Mic b (23 Myr Neptune-radius planet around an M1 star) and V1298 Tau c (30 Myr super-Neptune planet around a K1 star). We search for evidence of escaping metals by looking for excess absorption in lowly-ionized emission lines, such as C II and Si III, during three transits of each planet. We search for excess absorption in more highly-ionized species (e.g. Si IV and N V) to ensure any variability detected is from the transit and not from the star itself. For AU Mic b, we detect tentative evidence of excess absorption in CII and Si III during one transit, however we find similar variability in N V. For V1298 Tau c, we detect tentative evidence of excess absorption in Si III during one transit, but again find variability in Si IV. More transits with sampling across the entire transit could yield further insights into whether or not we can detect escaping metals from these uniquely young benchmark systems.