16290

Observational studies of planet-hosting T Tauri stars (TTS) provide crucial insight into the earliest evolutionary stages of planet formation at ages of a few Myr. In a exciting new discovery comma two giant protoplanets have been directly imaged orbiting in the disk gap of the nearby (113 pc) TTS PDS 70. The gap is gas-depleted comma directly exposing the protoplanets to UV and X-ray irradiation from the star. PDS 70 is the closest planet-hosting TTS discovered so far and viewed through very low extinction comma making it an exceptional target for UV spectroscopy with HST. We propose to obtain the first UV spectra of PDS 70 using STIS FUV (G140L) and NUV (G230L) gratings. Our main objectives are to determine the star.s accretion rate (which remains controversial) and use the UV spectra comma along with existing X-ray spectra comma to assess the impact of UV-X-ray irradiation on disk and protoplanet atmosphere ionization and heating. Stellar UV and X-ray emission influence disk dissipation and mass-loss comma thus affecting the timescale for planet-formation comma a key constraint for planet-formation models.