THE TUCANA/HOROLOGIUM, COLUMBA, AB DORADUS, AND ARGUS ASSOCIATIONS: NEW MEMBERS AND DUSTY DEBRIS DISKS

We propose 35 star systems within similar to 70 pc of Earth as newly identified members of nearby young stellar kinematic groups; these identifications include the first A-and late-B-type members of the AB Doradus moving group and field Argus Association. All but one of the 35 systems contain a bright solar-or earlier-type star that should make an excellent target for the next generation of adaptive optics (AO) imaging systems on large telescopes. AO imaging has revealed four massive planets in orbit around the lambda Boo star HR 8799. Initially, the planets were of uncertain mass due in large part to the uncertain age of the star. We find that HR 8799 is a likely member of the similar to 30 Myr old Columba Association, implying planet masses similar to 6 times that of Jupiter. We consider Spitzer Space Telescope MIPS photometry of stars in the similar to 30 Myr old Tucana/Horologium and Columba Associations, the similar to 40 Myr old field Argus Association, and the similar to 70 Myr old AB Doradus moving group. The percentage of stars in these young stellar groups that display excess emission above the stellar photosphere at 24 and 70 mu m wavelengths-indicative of the presence of a dusty debris disk-is compared with corresponding percentages for members of 11 open clusters and stellar associations with ages between 8 and 750 Myr, thus elucidating the decay of debris disks with time.