Gas accretion within the dust cavity in AB Aur
  AB Aur is a Herbig Ae star hosting a well-known transitional disk. Because of
its proximity and low inclination angle, it is an excellent object to study
planet formation. Our goal is to investigate the chemistry and dynamics of the
molecular gas component in the AB Aur disk, and its relation with the prominent
horseshoe shape observed in continuum mm emission. We used the NOEMA
interferometer to map with high angular resolution the J = 3-2 lines of HCO+
and HCN. By combining both, we can gain insight into the AB Aur disk structure.
Chemical segregation is observed in the AB Aur disk: HCO+ shows intense
emission toward the star position, at least one bright molecular bridge within
the dust cavity, and ring-like emission at larger radii, while HCN is only
detected in an annular ring that is coincident with the dust ring and presents
an intense peak close to the dust trap. We use HCO+ to investigate the gas
dynamics inside the cavity. The observed bright HCO+ bridge connects the
compact central source with the outer dusty ring. This bridge can be
interpreted as an accretion flow from the outer ring to the inner disk/jet
system proving gas accretion through the cavity.
