PENELLOPE

IV. A comparison between optical forbidden lines and H₂ UV lines in the Orion OB1b and σ-Ori associations^★

¹ ASI, Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy
e-mail: manuele.gangi@asi.it
² INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁴ Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, CO 80303, USA
⁵ Kavli Institute for Astronomy and Astrophysics, Peking University, Yiheyuan 5, Haidian Qu, 100871 Beijing, PR China
⁶ Department of Astronomy, Peking University, Yiheyuan 5, Haidian Qu, 100871 Beijing, PR China
⁷ INAF – Osservatorio Astronomico di Capodimonte – Salita Moiariello 16, 80131 Napoli, Italy
⁸ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), KonkolyThege Miklós út 15–17, 1121 Budapest, Hungary
¹⁰ CSFK, MTA Centre of Excellence, Konkoly-Thege Miklos út 15–17, 1121 Budapest, Hungary
¹¹ SETI Institute, 339 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
¹² Hamburg Observatory, Gojenbergsweg 11, 21029 Hamburg, Germany
¹³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁴ ELTE Eötvös Loránd University, Institute of Physics, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
¹⁵ INAF – Osservatorio Astronomico di Padova, Vicolo dell'osservatorio 5, 35122 Padova, Italy
¹⁶ National Astronomical Research Institute of Thailand (NARIT), Sirindhorn AstroPark, 260 Moo 4, T. Donkaew, A. Maerim, Chiangmai 50180, Thailand

Received: 30 March 2023
Accepted: 28 May 2023

Abstract

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.