Modeling the Spatial Distribution and Origin of CO Gas in Debris Disks

The detection of gas in debris disks raises the question of whether this gas is a remnant from the primordial protoplanetary phase, or released by the collision of secondary bodies. In this paper we analyze ALMA observations at 1″-1 5 resolution of three debris disks where the 12CO(2-1) rotational line was detected: HD 131835, HD 138813, and HD 156623. We apply the iterative Lucy-Richardson deconvolution technique to the problem of circumstellar disks to derive disk geometries and surface brightness distributions of the gas. The derived disk parameters are used as input for thermochemical models to test both primordial and cometary scenarios for the origin of the gas. We favor a secondary origin for the gas in these disks and find that the CO gas masses ( M ) require production rates (∼5 × 10−7 M⊕ yr−1) similar to those estimated for the bona fide gas-rich debris disk β Pic.