Chandra
Orion Ultradeep Project
X-ray irradiation of disks
It is well-established from visible and infrared light studies that young stars have a flattened structure of dusty gas swirling around them. The Hubble Space Telescope has directly imaged these disks, nicknamed proplyds, in the Orion Nebula. These are the protoplanetary disks where, extrasolar planet searches have shown, planets will often form. Recent theoretical studies have predicted that the behavior of these disks and the processes of planet formation will be significantly altered if the disks are slightly ionized. For example, the planets would form in a turbulent and lumpy disk rather than a smooth disk. The X-rays seen by COUP are the dominant source of ionizing radiation near these disks. But it is possible that X-ray irradiation does not efficiently occur, for example if the flares occur close to the stellar surface and only the inner disk edge is affected. The important question then arises:
Searching the strongest COUP sources with the hardest X-ray spectra, we have found several cases where the 6.4 keV fluorescent line is seen. We develop careful arguments that this arises from reflection off of the protoplanetary disk, and not intervening interstellar matter or the stellar surface.
The full paper on COUP X-ray reflection is:
Iron Fluorescent Line Emission from Young Stellar Objects in the Orion Nebula
M. Tsujimoto, E. D. Feigelson, N. Grosso, G. Micela, Y. Tsuboi, F. Favata, H. Shang, and J. H. Kastner
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X-ray irradiation of disks
It is well-established from visible and infrared light studies that young stars have a flattened structure of dusty gas swirling around them. The Hubble Space Telescope has directly imaged these disks, nicknamed proplyds, in the Orion Nebula. These are the protoplanetary disks where, extrasolar planet searches have shown, planets will often form. Recent theoretical studies have predicted that the behavior of these disks and the processes of planet formation will be significantly altered if the disks are slightly ionized. For example, the planets would form in a turbulent and lumpy disk rather than a smooth disk. The X-rays seen by COUP are the dominant source of ionizing radiation near these disks. But it is possible that X-ray irradiation does not efficiently occur, for example if the flares occur close to the stellar surface and only the inner disk edge is affected. The important question then arises:
Do the X-rays efficiently irradiate
the disk?
The irradiation of disks by X-rays is
already well-known in systems where the central object is a neutron star
or black hole, rather than a protostar. The signature of irradiation
there is the presence of a fluorescent emission line from cold iron atoms
at 6.4 keV, seen next to the hot plasma line around 6.7 keV.
Searching the strongest COUP sources with the hardest X-ray spectra, we have found several cases where the 6.4 keV fluorescent line is seen. We develop careful arguments that this arises from reflection off of the protoplanetary disk, and not intervening interstellar matter or the stellar surface.
The full paper on COUP X-ray reflection is:
Iron Fluorescent Line Emission from Young Stellar Objects in the Orion Nebula
M. Tsujimoto, E. D. Feigelson, N. Grosso, G. Micela, Y. Tsuboi, F. Favata, H. Shang, and J. H. Kastner
Back to the COUP home page