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arXiv · 2006.06590

Mid-infrared Studies of HD 113766 and HD 172555: Assessing Variability in the Terrestrial Zone of Young Exoplanetary Systems

Kate Y. L. Su·George H. Rieke·Carl Melis·Alan P. Jackson·Paul S. Smith·Huan Y. A. Meng·Andras Gaspar
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Abstract

We present multi-epoch infrared photometry and spectroscopy obtained with warm Spitzer, Subaru and SOFIA to assess variability for the young ($\sim$20 Myr) and dusty debris systems around HD 172555 and HD 113766A. No variations (within 0.5%) were found for the former at either 3.6 or 4.5 $μ$m, while significant non-periodic variations (peak-to-peak of $\sim$10-15% relative to the primary star) were detected for the latter. Relative to the Spitzer IRS spectra taken in 2004, multi-epoch mid-infrared spectra reveal no change in either the shape of the prominent 10 $μ$m solid-state features or the overall flux levels (no more than 20%) for both systems, corroborating that the population of sub-$μ$m-sized grains that produce the pronounced solid-state features is stable over a decadal timescale. We suggest that these sub-$μ$m-sized grains were initially generated in an optically thick clump of debris of mm-sized vapor condensates resulting from a recent violent impact between large asteroidal or planetary bodies. Because of the shielding from the stellar photons provided by this clump, intense collisions led to an over-production of fine grains that would otherwise be ejected from the system by radiation pressure. As the clump is sheared by its orbital motion and becomes optically thin, a population of very fine grains could remain in stable orbits until Poynting-Robertson drag slowly spirals them into the star. We further suggest that the 3-5 $μ$m disk variation around HD 113766A is consistent with a clump/arc of such fine grains on a modestly eccentric orbit in its terrestrial zone.

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Kate Y. L. Su, George H. Rieke, Carl Melis, Alan P. Jackson, Paul S. Smith, Huan Y. A. Meng, Andras Gaspar. 2020-06-11. Mid-infrared Studies of HD 113766 and HD 172555: Assessing Variability in the Terrestrial Zone of Young Exoplanetary Systems. https://doi.org/10.3847/1538-4357%2Fab9c9b

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