REMNANT DUSTY DISKS IN LINDROOS POST T TAURI openParPTTclosePar STARS

the purpose of this proposal is to obtain isocam imaging observations of lindroos wide binary systems at two wavelengths (6.7mu and 15mu). lindroos binaries are physical systems consisting of an earlytype main sequence primary and a latetype premain sequence(pms)secondary, typically a bright bstar with a faint kstar or gstar companion. these coeval pairs span a range of ages between 10 and 120 myr and a range of projected separations of 10 to 30 arcsec (10006000 au). the secondaries thus constitute a perfect sample of ptt stars, i.e. stars older than the weakline t tauri stars but not yet on the zams. we have already used these systems to study the evolution of xray emission as a function of time (with the rosat hri) and now intend to use them in order to investigate how disk properties vary in the age gap between the t tauri phase and the zams. we have also tried to detect dust emission using groundbased facilities like the sest but could not detect it, since it is likely to be very weak. iso observations are of the order of 100 times more sensitive to to detect small amounts of micronsized dust particles than groundbased observations and should thus allow us to probe the timescale for planet formation around solartype stars near a more massive hot star, i.e. in a binary environment where additional dynamical and radiation effects may operate on the ptt star.s disk. we have 10/12 lindroos systems available for each launch window, some of which have been detected at 12 microns in the iras fsc. for these systems isocam imaging is especially rewarding, since we can resolve the iras emission and pinpoint its spatial distribution (is it dust emission from a remnant disk of the lowmass pms star, or is it photospheric emission from the brighter highermass star?) in these cases, additional 60 and 90 mu isophot photometry will be carried out (pht22_c100), in order to search for col truncated!, Pl [truncated!, Please see actual data for full text]