The ¹²CO gas structures of protoplanetary disks in the Upper Scorpius region

¹ Dipartimento di Fisica ‘Aldo Pontremoli’, Università degli Studi di Milano, via G. Celoria 16, 20133 Milano, Italy
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany
³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Joint ALMA Observatory, Avenida Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁵ University College Dublin (UCD), Department of Physics, Belfield, Dublin 4, Ireland
⁶ Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
⁷ Max-Planck-Institut fur Astronomie (MPIA), Konigstuhl 17, 69117 Heidelberg, Germany
⁸ Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
¹⁰ Department of Astronomy, University of Michigan, 1085 South University Avenue, Ann Arbor, MI 48109, USA
¹¹ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹³ Academia Sinica Institute of Astronomy and Astrophysics, 11F of Astronomy-Mathematics Building, AS/NTU, No. 1, Sec. 4, Roosevelt Rd, Taipei 106216, Taiwan

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Received: 22 September 2025
Accepted: 18 November 2025

Abstract

We present measurements of key protoplanetary disk properties inferred from parametric models of ALMA ¹²CO spectral line visibilities. We derived gas-disk radii, integrated fluxes, optically thick emission layers, and brightness temperature profiles for the disk population of the old (4–14 Myr) Upper Scorpius star-forming region. We measured CO emission sizes for 37 disks with bright CO J = 3–2 emission (S/N > 10 on the integrated flux; out of the 83 disks with CO detections), finding that the median radius containing 90% of the flux is ∼82 au, with radii spanning from 22 up to 247 au. We report a correlation between the ¹²CO brightness temperatures and stellar luminosities, with a Pearson coefficient of 0.6, which we used to prove that the ¹²CO optically thick emission layer primarily emanates from a region below the superheated dust, which is optically thin to the stellar irradiation. Moreover, we derive 33 CO emission-surface height profiles, finding a median aspect ratio of ⟨z/r⟩ ∼ 0.16 in a range from ∼0.01 up to ∼0.45 over the sample. Finally, we comment on the multiple systems in our sample, of which only some were already known. These results confirm that it is possible to derive bulk disk properties by modeling moderate-angular-resolution ALMA visibilities.