  Transitional disks with large dust cavities are important laboratories to
study planet formation and disk evolution. Cold gas may still be present inside
these cavities, but the quantification of this gas is challenging. The gas
content is important to constrain the origin of the dust cavity. We use Atacama
Large Millimeter/submillimeter Array (ALMA) observations of 12CO 6--5 and 690
GHz (Band 9) continuum of five well-studied transitional disks. In addition, we
analyze previously published Band 7 observations of a disk in 12CO 3--2 line
and 345 GHz continuum. The observations are used to set constraints on the gas
and dust surface density profiles, in particular the drop delta-gas of the gas
density inside the dust cavity. The physical-chemical modeling code DALI is
used to analyze the gas and dust images simultaneously. We model SR21,
HD135344B, LkCa15, SR24S and RXJ1615-3255 (Band 9) and J1604-2130 (Band 7). The
SED and continuum visibility curve constrain the dust surface density.
Subsequently, the same model is used to calculate the 12CO emission, which is
compared with the observations through spectra and intensity cuts. The amount
of gas inside the cavity is quantified by varying the delta-gas parameter.
Model fits to the dust and gas indicate that gas is still present inside the
dust cavity for all disks but at a reduced level. The gas surface density drops
inside the cavity by at least a factor 10, whereas the dust density drops by at
least a factor 1000. Disk masses are comparable with previous estimates from
the literature, cavity radii are found to be smaller than in the 345 GHz
SubMillimeter Array (SMA) data. The derived gas surface density profiles
suggest clearing of the cavity by one or more companions in all cases, trapping
the millimeter-sized dust at the edge of the cavity.
