HYSOVAR: Circumstellar Disks Variability around Young Stellar Objects in the Orion Nebula Cluster with Herschel/PACS

The variability of Young Stellar Objects (YSOs) have been demonstrated over half a century ago from optical observations. More recent time series photometry of YSOs in the thermal infrared have shown their great potential to probe the structure of inner circumstellar disks (r << 1 AU), in particular the presence of warps and .clouds. in the disks which may owe their existence to the gravitational torques from closein planets. For instance the YSOVAR program used the Spitzer IRAC instrument to monitor over 1400virgulYSOs and establish that 70% of them show significant variability in the midIR. Today the Herschel/PACS spectral coverage, sensitivity and stability offer a unique opportunity to access the wavelength regime sensitive to the dust thermal emission from the terrestrial habitable zone through the iceline where gas giants are expected to form.We propose the HYSOVAR program, an expansion of YSOVAR with the Herschel/PACS Photometer, to monitor the flux variations of 100+ Class I YSOs in Orion over weekstoyears time scales. This small (9.9 hours) exploratory program would greatly increase the statistics and sensitivity of previous studies in the farIR, and it would help us identify the physical processes responsible for the observed infrared variability by placing strong constraints on existing models of star and planet formation. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]