We analyze high angular resolution ALMA observations of the TW Hya disk to place constraints on the CO and dust properties .
We present new , sensitive observations of the ^ { 12 } CO J = 3 - 2 line at a spatial resolution of 8 AU ( 0 \farcs 14 ) .
The CO emission exhibits a bright inner core , a shoulder at r \approx 70 AU , and a prominent break in slope at r \approx 90 AU .
Radiative transfer modeling is used to demonstrate that the emission morphology can be reasonably reproduced with a ^ { 12 } CO column density profile featuring a steep decrease at r \approx 15 AU and a secondary bump peaking at r \approx 70 AU .
Similar features have been identified in observations of rarer CO isotopologues , which trace heights closer to the midplane .
Substructure in the underlying gas distribution or radially varying CO depletion that affects much of the disk ’ s vertical extent may explain the shared emission features of the main CO isotopologues .
We also combine archival 1.3 mm and 870 \mu m continuum observations to produce a spectral index map at a spatial resolution of 2 AU .
The spectral index rises sharply at the continuum emission gaps at radii of 25 , 41 , and 47 AU .
This behavior suggests that the grains within the gaps are no larger than a few millimeters .
Outside the continuum gaps , the low spectral index values of \alpha \approx 2 indicate either that grains up to centimeter size are present , or that the bright continuum rings are marginally optically thick at millimeter wavelengths .