A Disk Census for the Nearest Group of Young Stars: Mid-Infrared Observations of the TW Hydrae Association

A group of young, active stars in the vicinity of TW Hydrae has recently beenidentified as a possible physical association with a common origin. Given itsproximity ($\sim$50 pc), age ($\sim$10 Myr) and abundance of binary systems,the TW Hya Association is ideally suited to studies of diversity and evolutionof circumstellar disks. Here we present mid-infrared observations of 15candidate members of the group, 11 of which have no previous flux measurementsat wavelengths longer than 2$\mu$m. We report the discovery of a possible10$\mu$m excess in CD -33$^{\circ}$7795, which may be due to a circumstellardisk or a faint, as yet undetected binary companion. Of the other stars, onlyTW Hya, HD 98800, Hen 3-600A, and HR 4796A -- all of which were detected byIRAS -- show excess thermal emission. Our 10$\mu$m flux measurements for theremaining members of the Association are consistent with photospheric emission,allowing us to rule out dusty inner disks. In light of these findings, wediscuss the origin and age of the TW Hya Association as well as implicationsfor disk evolution timescales.Comment: 10 pages and 1 PostScript figure, accepted for publication in The Astrophysical Journal Letter