Letter to the Editor

An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS in a protoplanetary disk

¹ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon, Korea
e-mail: tpnguyen@kasi.re.kr
² Department of Astrophysics, Vietnam National Space Center, Vietnam Academy of Science and Techonology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam
³ Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, Allée Geoffroy, Saint-Hilaire, 33615 Pessac, France
⁴ IRAM, 300 Rue de la piscine, 38406 Saint Martin d’Hères Cedex, France
⁵ Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, New York 13346, USA
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA
⁷ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS-OMP, CNRS, CNES, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
⁸ Instituto de Ciencias Químicas Aplicadas, Facultad de Ingeniería, Universidad Autónoma de Chile, Av. Pedro de Valdivia 425, 7500912 Providencia, Santiago, Chile
⁹ School of Earth and Planetary Sciences, National Institute of Science Education and Research, HBNI, Jatni, 752050 Odisha, India
¹⁰ University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
¹¹ Institut des Sciences Moléculaires, UMR5255-CNRS, 351 Cours de la libration, 33405 Talence, France
¹² Academia Sinica Institute of Astronomy and Astrophysics, PO Box 23-141 Taipei 106, Taiwan

Received: 27 July 2021
Accepted: 27 August 2021

Abstract

Context. Molecular line surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs), the birthplace of planets. The large radial and vertical temperature as well as density gradients in these PPDs lead to a complex chemical composition, making chemistry an important step to understand the variety of planetary systems.

Aims. We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T Tauri system.

Methods. We used NOEMA with the new correlator PolyFix to observe rotational lines at ∼2.6 to 4 mm from a few dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance relative to ¹³CO, which we compare to those of the TMC1 cloud and LkCa 15 disk.

Results. We report the first detection of CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of them had been found previously, while seven others (¹³CN, N₂H⁺, HNC, DNC, HC₃N, CCS, and C³⁴S) are new detections in this disk.

Conclusions. The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived from DCO⁺/HCO⁺, DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detection of the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks to its large disk size and mass.