2023A&A...675A.153G

Context. Observing the spatial distribution and excitation processes of atomic and molecular gas in the inner regions (<20 au) of young (<10 Myr) protoplanetary disks helps us to understand the conditions for the formation and evolution of planetary systems.
Aims. In the framework of the PENELLOPE and ULLYSES projects, we aim to characterize the atomic and molecular component of protoplanetary disks in a sample of 11 classical T Tauri stars of the Orion OB1 and σ-Orionis associations.
Methods. We analyzed the flux-calibrated optical forbidden lines and the fluorescent ultraviolet H₂ progressions using spectra acquired with ESPRESSO at VLT, UVES at VLT, and HST-COS. Line morphologies were characterized through Gaussian decomposition. We then focused on the properties of the narrow low-velocity (full width half maximum <40 km s^–1 and |υ_p| < 30 km s^–1) component (NLVC) of the [O I] 630 nm line and compared them with those of the UV-H₂ lines.
Results. We found that the [O I]630 NLVC and the UV-H₂ lines are strongly correlated in terms of peak velocities, full width at half maximum values, and luminosity. Assuming that the line width is dominated by Keplerian broadening, the [O I]630 NLVC originates from a disk region between 0.5 and 3.5 au, while that of UV-H₂ originates in a region from 0.05 to 1 au. The luminosities of [O I]630 NLVC and UV-H₂ correlate with an accretion luminosity with a similar slope, as well as with the luminosity of the C IV154.8, 155 nm doublet. We discuss such correlations in the framework of the currently suggested excitation processes for the [O I]630 NLVC.
Conclusions. Our results can be interpreted in a scenario in which the [O I]630 NLVC and UV-H₂ have a common disk origin with a partially overlapped radial extension. We also suggest that the excitation of the [O I] NLVC is mainly induced by stellar far-ultraviolet continuum photons, than being of mostly thermal origin. This study demonstrates the potential of contemporaneous wide-band highresolution spectroscopy in linking different tracers of protoplanetary disks.