Letter to the Editor

Edge-On Disk Study (EODS)

I. Thermal structure of the Flying Saucer disk

¹ Univ. Bordeaux, CNRS, Laboratoire d’Astrophysique de Bordeaux (LAB), UMR 5804, F-33600 Pessac, France
² Departamento de Física, Facultad de Ciencias, Universidad de Chile, Av. Las Palmeras 3425, Ñuñoa, Santiago, Chile
³ Dipartimento di Fisica e Astronomia “Augusto Righi”, ALMA Mater Studiorum – Universiti. Bologna, Via Gobetti 93/2, I-40190 Bologna, Italy
⁴ Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, D-69117 Heidelberg, Germany
⁵ Department of Chemistry, Ludwig-Maximilians-Universität, Butenandtstr. 5-13, D-81377 München, Germany
⁶ IRAM, 300 Rue de la Piscine, F-38406 Saint Martin d’Hères, France
⁷ Institut des Sciences Moléculaires d’Orsay, CNRS, Univ. Paris-Saclay, Orsay, France
⁸ RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
⁹ Carl Sagan Center, SETI Institute, Mountain View, CA, USA
¹⁰ Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
¹² LUX, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 92190 Meudon, France
¹³ Exoplanets and Planetary Formation Group, School of Earth and Planetary Sciences, National Institute of Science Education and Research, Jatni, 752050 Odisha, India
¹⁴ National Astronomical Observatory of Japan, Division of Science, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 Kanto, Japan
¹⁵ Vietnam National Space Center, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet, Nghia Do, Cau Giay, Ha Noi, Vietnam
¹⁶ Academia Sinica Institute of Astronomy and Astrophysics, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec.4,Roosevelt Rd, Taipei 106319, Taiwan, R.O.C.
¹⁷ Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität zu Kiel, Leibnizstraße 15, 24118 Kiel, Germany

^⋆ Corresponding author: stephane.guilloteau@u-bordeaux.fr

Received: 29 March 2025
Accepted: 3 July 2025

Abstract

Context. The dust and gas temperature in protoplanetary disks play critical roles in determining their chemical evolution and influencing planet formation processes.

Aims. We attempted an accurate measurement of the dust and CO temperature profile in the edge-on disk of the Flying Saucer.

Methods. We used the unique properties of the Flying Saucer – its edge-on geometry and its fortunate position in front of CO clouds with different brightness temperatures – to provide independent constraints on the dust temperature. We compared it with the dust temperature derived using the radiative transfer code DISKFIT and the CO gas temperature.

Results. We find clear evidence of a substantial gas temperature vertical gradient, with a cold (10 K) disk mid-plane and a warmer CO layer where T(r)≈27 (r/100 au)^−0.3 K. Direct evidence of CO depletion in the mid-plane, below about 1 scale height, is also found. At this height, the gas temperature is 15–20 K, consistent with the expected CO freeze-out temperature. The dust disk appears optically thin at 345 GHz, and exhibits moderate settling.