scientific abstract although there is now compelling evidence that many young stellar objects (ysos) are surrounded by disks, e.g. the classical t tauri stars (cttss) and some herbig ae/be stars, it is not clear how, and at what rate, such disks evolve. certainly by the time these stars have reached the main sequence, most of the disk material has either disappeared or coagulated into larger bodies. what causes a disk to dissipate: is it accretion, the presence of winds, or the formation of larger bodies like planets? in order to address this problem one must look at stars older than the cttss since these stars are at most a few myrs old and it takes typically a 100 myrs before they finally settle on the zams. the region in the hr diagram between the cttss and the main sequence is occupied by the post-t tauri stars (pttss). it is proposed to obtain multi-band photometry with pht of a sample of evolved pre-main sequence stars to measure their mid- to far-infrared spectral energy distributions. by comparing the spectral energy distributions of these stars with those of cttss it is hoped to see evidence for the evolution of circumstellar disks from the accretion phase right through to the dissipation of the surrounding dust and perhaps the earliest stages of planetary formation. another fundamental question it is intended to address, in connection with disk evolution, is whether weak-line t tauri stars (wttss) are simply cttss devoid of circumstellar matter, as has been claimed. wttss and cttss are located in the same region of the hr diagram and are of approximately the same age. the increased sensitivity of iso, in comparison with iras, will allow for a much deeper search for material around wttss than has hitherto been possible. observational summary the target list is largely made up of sources that were not detected by iras or, if detected, their fluxes are poorly known. in all cases, observations will be made with 9 filters: p-4.85, p-7.7, p-10, p-11.5, p-12.8, p-16, p-20, p-60 and p-100 using aot pht03. even for those sources that were detected by iras we will obtain much more detailed spectral energy distribution curves than has hitherto been possible and at the same time we will test for silicate and pah features. the integration time is 32 sec for all filters using rectangular chopping mode. for the p-4.85, p-7.7, p-10, p-11.5 and p-12.8 observations, an aperture of 10 arcseconds will be used. for the p-16 and p-20 observations an aperture of 23 arcseconds will be employed and finally an aperture of 120 arcseconds for the p-60 and p-100 observations.
Instrument
PHT03
Temporal Coverage
1996-03-10T11:25:45Z/1996-07-14T08:28:36Z
Version
1.0
Mission Description
The Infrared Space Observatory (ISO) was the worlds first true orbiting infrared observatory. Equipped with four highly-sophisticated and versatile scientific instruments, it was launched by Ariane in November 1995 and provided astronomers world-wide with a facility of unprecedented sensitivity and capabilities for a detailed exploration of the Universe at infrared wavelengths.
European Space Agency, Ray et al., 1999, 'The Evolution of Disks Around Young Low Mass Stars ', 1.0, European Space Agency, https://doi.org/10.5270/esa-o1atin4
