SPITZER and HST Observations of Photoevaporating Disks
First Author:
Zoltan Balog
Email: zbalog AT as.arizona.edu
Steward Observatory, University of Arizona
933. N. Cherry Av.
Tucson, AZ, 85721, USA
Coauthors:
Rieke, George H., Steward Observatory, University of Arizona
Su, Kate Y. L., Steward Observatory, University of Arizona
Muzerolle, James, Steward Observatory, University of Arizona
Gaspar, Andras, Steward Observatory, University of Arizona
Bally, John, Center for Astrophysics and Space Astronomy University of Colorado at Boulder
Abstract
I will discuss Spitzer and HST observations of protoplanetary disks being photoevaporated around high-mass O-type stars. 24 micron observations show that these objects have ``cometary'' structure, where the dust pulled away from the disk is forced away from the O star by photon pressure. Models of the 24 and 8 micron brightness profiles agree with this hypothesis. We find no Pa alpha emission in any of the systems. The resulting upper limits correspond to about 0.000002-0.000003 solar mass of mass in hydrogen in the tails suggesting that the gas is severely depleted. The IRAC data and the low resolution 5-12 micron IRS spectra provide evidence for an inner disk while high resolution long wavelength (14-30 micron) IRS spectra confirm the presence of a gas free ``tail'' that consists of ~0.01 to ~1 micron dust grains originating in the outerparts of the circumstellar disks. Overall our observations support theoretical predictions in which photoevaporation removes the gas relatively quickly from the outer region of a protoplanetary disk but leaves an inner more robust and possibly gas-rich disk component of radius 5-10 AU. With the gas gone, larger solid bodies in the outer disk can experience a high rate of collisions and produce elevated amounts of dust. This dust is being stripped from the system by the photon pressure of the O star to form a gas-free dusty tail.
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