HST UV Spectroscopy of the Planet-Hosting T Tauri Star PDS 70

Abstract

We summarize Hubble Space Telescope (HST) UV observations of the weak-lined T Tauri star (wTTS) PDS 70 obtained with the Space Telescope Imaging Spectrograph (STIS). These observations provide the first far-UV (FUV) and near-UV (NUV) spectra of PDS 70. Ground-based observations have so far revealed two formative giant planets orbiting in a wide gap in its circumstellar disk. Both the star and young planets are thought to still be accreting. The HST spectra provide new insight into physical conditions in the star's outer atmosphere and circumstellar environment. The spectra are dominated by chromospheric and transition region emission lines with maximum formation temperatures log T = 4.5 - 5.2 K. Stellar continuum emission is present in the NUV but we find no significant FUV continuum, as could arise from accretion shocks. Several fluorescent FUV H2 emission lines are present, a surprising result since H2 lines are usually undetected in wTTS. The H2 lines likely originate in irradiated circumstellar gas that could serve as a reservoir for the star's waning accretion. A previously established correlation between C IV line luminosity and accretion rate yields ${\dot{M}}_{acc}$ $\sim$ 10${}^{-10}$ $M_{\odot }$ yr${}^{-1}$, consistent with previous estimates. ALMA disk gas models imply strong absorption of stellar X-ray and UV (XUV) radiation near the star, effectively shielding the planets. Inner disk gas is exposed to ongoing photoevaporation by XUV radiation and the disk is nearing the end of its expected lifetime, making PDS 70 an important example of a young planet-hosting star in the late stage of accretion.

21 pages, 7 figures

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Cited by in corpus (4)

• Water in the terrestrial planet-forming zone of the PDS 70 disk
• PDS 70 unveiled by star-hopping: total intensity, polarimetry and mm-imaging modeled in concert
• X-ray and UV radiation in the planet-forming T-Tauri system PDS 70. Signs of accretion and coronal activity
• Updated Ultraviolet Fluorescence Efficiencies of CS: Evidence for Model Discrepancies in the Enhancement of NUV-Derived CS Abundances in Comets