HD141569A system ALMA and NOEMA data cubes

The continuum emission is equally shared between a compact (<50au) and a smooth, extended dust component (~350 au). Large millimetre grains seem to dominate the inner regions, while the dust spectral index is marginally larger in the outer region. The ^12^CO is optically thick, while ^13^CO is optically thin with tau_13CO_~0.15 (C^18^O is not detected).

The ^13^CO surface density is constrained to be one order of magnitude smaller than around younger Herbig Ae stars, and we derive a gas mass M_12CO_=10^-1^M_{sun}_. We confirm the presence of a small CO cavity (R_CO_=17+/-3au), and find a possibly larger radius for the optically thin ^13^CO J=2-1 transition (35+/-5au). We show that the observed CO brightness asymmetry is coincident with the complex ring structures discovered with VLT/SPHERE in the inner 90au.

The ^12^CO temperature T_0_(100au)~30K is lower than expected for a Herbig~A0 star, and could be indicative of subthermal excitation. With the largest amount of dust and gas among hybrid discs, HD141569A shows coincident characteristics of both protoplanetary discs (central regions), and debris discs at large distance. Together with its morphological characteristics and young age, it appears to be a good candidate to witness the transient phase of gas dissipation, with an apparently large gas-to-dust ratio (G/D>100) favouring a faster evolution of dust grains.