Context :

Aims : The aim of this work is to study the structure of the protoplanetary disk surrounding the Herbig Ae star HD 163296 .

Methods : We have used high-resolution and high-sensitivity ALMA observations of the { CO } ( 3 – 2 ) emission line and the continuum at 850 \mu { m } , as well as the 3- dimensional radiative transfer code MCFOST to model the data presented in this work .

Results : The { CO } ( 3 – 2 ) emission unveils for the first time at sub-millimeter frequencies the vertical structure details of a gaseous disk in Keplerian rotation , showing the back- and the front-side of a flared disk .
Continuum emission at 850 \mu { m } reveals a compact dust disk with a 240 { AU } outer radius and a surface brightness profile that shows a very steep decline at radius larger than 125 { AU } .
The gaseous disk is more than two times larger than the dust disk , with a similar critical radius but with a shallower radial profile .
Radiative transfer models of the continuum data confirms the need for a sharp outer edge to the dust disk .
The models for the { CO } ( 3 – 2 ) channel map require the disk to be slightly more geometrically thick than previous models suggested , and that the temperature at which CO gas becomes depleted ( frozen-out ) from the outer regions of the disk midplane is T < 20 { K } , in agreement with previous studies .

Conclusions :