Timescales of Disk Evolution and Planet Formation: HST, Adaptive Optics, and ISO Observations of Weak-Line and Post-T Tauri Stars

摘要: We present high spatial resolution HST and ground-based adaptive optics observations high-sensitivity ISO (ISOCAM & ISOPHOT) of a sample X-ray selected weak-line (WTTS) post? (PTTS) T Tauri stars located in the nearby Chamaeleon Scorpius-Centaurus OB associations. HST/NICMOS aimed at identifying substellar companions (young brown dwarfs) separations ?30 AU from primary stars. No such objects were found within 300 any target stars, number faint larger can very likely be attributed to population field (background) ISOCAM 5 15 Myr old WTTSs PTTSs ScoCen reveal infrared excesses which are clearly above photospheric levels have spectral index intermediate between that younger (1 Myr) pure stellar photospheres. The difference older compared with classical TTSs Cha deficiency smaller size (0.1 1 ?m) dust grains relative (?5 disks PTTSs. lack small is either due environment (effect O supernova explosions) or disk evolution. If latter case, it would hint circumstellar start become depleted an age Myr. Dust depletion related build-up particles (ultimately rocks planetesimals) thus indicator for onset period planet formation.