The following document lists the file abstract/TPRUSTI_VARISED1.abs
from catalogue VI/111.
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We propose to measure the spectral energy distribution (SED) of an important subgroup of relatively "old" pre-main-sequence stars (the UX Ori-type stars, also called Algol-type young stars) which appear to be in the transition phase between accretion and full disruption and dissipation of their disk, an epoch at which planets may form. These stars differ from other (younger?) pre-main-sequence stars because they show evidence of variable circumstellar extinction, due to clouds of dust in orbit around the star, and of high-velocity infalling gas, probably produced by the dissipation of cometary bodies in star-grazing orbits. A small number of these stars is currently monitored by ISO for variability, also very likely associated with dust clouds arriving in the vicinity of the star along elongated orbits. - A crucial information needed to understand the properties of circumstellar matter (and one required by the analysis of variability data) is good SEDs over the largest possible range of wavelengths. At the time of the first ISO call, measurements of the SED of most of the known UX Ori stars were planned in the various core programs on pre-main-sequence stars. However, it appears now that the observations obtained so far are limited to few stars and lack the systematic quality we require. In particular, the variability data demonstrate the need to obtain the overall SED at the same epoch. Moreover, the number of stars identified as UX Ori-type stars has increased, and a statistical approach to their properties has become possible.