New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297

Moór, Attila and Kral, Quentin and Ábrahám, Péter and Kóspál, Ágnes and Dutrey, Anne and Pawellek, Nicole (2019) New Millimeter CO Observations of the Gas-rich Debris Disks 49 Cet and HD 32297. ASTROPHYSICAL JOURNAL, 884. ISSN 1538-4357

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Abstract

Previous observations revealed the existence of CO gas at nearly protoplanetary level in several dust-rich debris disks around youn A-type stars. Here we used the Atacama Large Millimeter/submillimete Array (ALMA) 7 m Array to measure 13CO and C18 emission toward two debris disks, 49 Cet and HD 32297, and detecte similarly high CO content (>0.01 M ⊕). These high C masses imply a highly efficient shielding of CO molecules agains stellar and interstellar ultraviolet photons. Adapting a recen secondary gas disk model that considers both shielding by carbon atom and self-shielding of CO, we can explain the observed CO level in bot systems. Based on the derived gas densities we suggest that, in the H 32297 disk, dust and gas are coupled and the dynamics of small grains i affected by the gaseous component. For 49 Cet, the question of couplin remains undecided. We found that the main stellar and disk properties o 49 Cet and HD 32297 are very similar to those of previously identifie debris disks with high CO content. These objects constitute together th first known representatives of shielded debris disks

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