Evaporating Disks
Evaporation in the vicinity of an O star disrupts protoplanetary disks, as seen in the Orion
proplyds. We have found a number of evaporating disks with Spitzer, which are in some ways more
dramatic and better oriented for detailed study than the proplyds ? they have cometary tails
extending up to 0.1 pc from the evaporation working surface. We will use Spitzer/IRS and
HST/NICMOS to investigate these systems in more detail. We want to explore the excitation
condition in the gas, both in the head and in the tail where possible. We will measure the effects of
evaporation on the characteristic emission features of the dust. We also will use NICMOS to image
them in detail, including mapping complex structures resolved in their tails at 24 microns
With HST, we will carry out observations using NICMOS/NIC2 and F164N, F166N, F187N, F190N, F212N, F215N filters. We will use two orbits for each of our closest objects (IC1396, NGC2264) to achive the highest signal to noise ratio possible to study the structures of the tails in Pa alpha images. THe remaining one orbit will be used for the thitrd (farthest object)
That is why we divided the orbits the following way. Using our 24 fluxes we calculated the exposure times needed to reach a signal tonoise ratio of 100 in the F212N, F215N, F164N and F166N filters (about 100s each) and distributed the remaining time for the Pa alpha and its continuum filter. This should provide enough signal to detect the structure in the tail in the case of IC1396 in spite of a complex and high background due to the leftovers of the HII region. It will let us search for structure in the tails of the other objects.
We are going to use dithered observations to effectively remove the detector artifacts and possible cosmic ray hits. Considering the nearby bright O star and the extended nature of our objects we need to carefully select the pointing and the dither pattern. We plan to place our object's "head" as near the edge of the detector which is closer to the O star as it is allowed by the pointing accuracy and use a four point linear dither pattern in the case of IC1396 and NGC2264. This way we can make sure that we capture the whole tail structure and get as little scattered light from the bright source as possible. In case of NGC2244 we reduced the number of dithers to two in order to enable longer observing time which gives higher S/N.
12
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