2024A&A...685A.126S

Context. The physics and chemistry of planet-forming disks are far from being fully understood. To make further progress, both broad line surveys and observations of individual tracers in a statistically significant number of disks are required.
Aims. Our aim is to perform a line survey of eight planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning).
Methods. Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ∼80 lines from > 20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210-280 GHz with a 1σ rms sensitivity of ∼8-12 mJy beam^–1 at a 0.9″ and 0.3 km s^–1 resolution will be completed in 2024. The uv visibilities are fitted with the DiskFit model to obtain key stellar and disk properties.
Results. In this first paper, the combined ¹²CO, ¹³CO, and C¹⁸O J = 2-1 data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrained dynamical stellar masses, geometries, temperatures, the CO column densities, and gas masses for each disk. The best-fit temperatures at 100 au are ∼ 17-37 K, and decrease radially with the power-law exponent q ∼ 0.05-0.76. The inferred CO column densities decrease radially with the power-law exponent p ∼ 0.2-3.1. The gas masses estimated from ¹³CO (2-1) are ∼0.001-0.2 M_⊙.
Conclusions. Using NOEMA, we confirm the presence of temperature gradients in our disk sample. The best-fit CO column densities point to severe CO freeze-out in these disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions. The high ¹³CO/C¹⁸O ratio of ∼23 in DM Tau could be indicative of strong selective photodissociation of C¹⁸O in this disk.