Tracing the gas surface density profile the inner disk of transition disks with VLT/CRIRES

To derive the surface density inside the dust cavities of transition disks is paramount to understand their origin. We performed deep observations of CO emission at 4.7 micron of the transition disks HD 139614 and HD 169142 with VLT/CRIRES. We detect 12CO, 13CO, and C18O emission in the sources. We model the CO isotopologues emission-line profiles, spectroastrometry signature, and rotational diagrams with a grid of flat Keplerian disks in LTE. We find 12CO gas emission inside the dust cavity (R=6au for HD 139614, R=20 au for HD 169142) down to a radius of 0.5 - 1 au. We find strong evidence for gas density drops inside the dust cavities, however, we dont find evidence for gas gaps larger than 3 au in the disk. Our models suggest NH column densities inside the dust cavity of 5x10^19-10^21 cm^-2 (10^-4 - 2x10^-3 g cm^-2) assuming a NCO/NH = 10^-4. These column densities are lower than the extrapolated gas surface density from the outer disk and are hard to reconcile with the accretion rates measured for the objects (10^-8 and 10^-9 Msun/yr for HD 139614, HD 169142 respectively). Gas density drops and no gas gaps are consitent with the pressence of a