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Image of S. Witte

S. Witte

Research: Dust clouds in ultracool atmospheres

A large fraction of the gas of cool stellar atmospheres is comprised of molecules. With decreasing effective temperature the complexity and abundance of molecules in the atmospheres increases. For objects with effective temperatures below 2800K, the atmospheres are cool and dense enough to feature a strong supersaturation of the gas phase. Hence, molecules from the gas phase start to condense out. While some molecules condense by polymerisation, other require a preexisting surface in order to form more complex solids. The resulting particles settle gravitationally while growing, thereby depleting the local gas of heavy elements. Reaching the deeper atmosphere, those particle evaporate. The released elements are transported back upwards by convective overshooting. I am using the stellar atmosphere code DRIFT-PHOENIX, which consistently determines a 1D atmosphere structure, an equilibrium between forming/settling dust particles and the element replenishment by convective overshooting as well as the respective radiation field.

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