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The gaseous molecular disk that orbits the main sequence A-type star 49 Cetihas been known since 1995, but the stellar age and the origin of the observedcarbon monoxide molecules have been unknown. We now identify 49 Ceti as amember of the 40 Myr old Argus Association and present a colliding comet modelto explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-typestar HD 21997. The model suggests that massive -- 400 Earth mass -- analogs ofthe Sun's Kuiper Belt are in orbit about some A-type stars, that these largemasses are composed primarily of comet-like objects, and that these objects arerich in CO and perhaps also CO2. We identify additional early-type members ofthe Argus Association and the Tucana/Horologium and Columba Associations; someof these stars display excess mid-infrared emission as measured with theWidefield Infrared Survey Explorer (WISE).

A 40 Myr Old Gaseous Circumstellar Disk at 49 Ceti: Massive CO-Rich Comet Clouds at Young A-Type Stars