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Previous observations revealed the existence of CO gas at nearlyprotoplanetary level in several dust-rich debris disks around young A-typestars. Here we used the ALMA 7m-array to measure $^{13}$CO and C$^{18}$Oemission toward two debris disks, 49 Cet and HD 32297, and detected similarlyhigh CO content ($>$0.01M$_\oplus$). These high CO masses imply a highlyefficient shielding of CO molecules against stellar and interstellarultraviolet photons. Adapting a recent secondary gas disk model that considersboth shielding by carbon atoms and self-shielding of CO, we can explain theobserved CO level in both systems. Based on the derived gas densities wesuggest that, in the HD 32297 disk, dust and gas are coupled and the dynamicsof small grains is affected by the gaseous component. For 49 Cet, the questionof coupling remains undecided. We found that the main stellar and diskpropertiesof 49 Cet and HD 32297 are very similar to those of previouslyidentified debris disks with high CO content. These objects constitute togetherthe first known representatives of shielded debris disks.

New millimeter CO observations of the gas-rich debris disks 49 Cet and HD 32297