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Astrophysics Colloquium

Characterizing Brown Dwarf Atmospheres with Multi-wavelength Observations
Presented by Theodora Karalidi
Department of Astronomy and Astrophysics, University of California, Santa Cruz

Thursday, November 15, 2018
11:00 A.M. in 169-336

Abstract
Brown dwarfs of spectral types Y to L span temperatures from a few hundred to 2000K and a wide range of gravities. Their atmospheres are full of clouds in complex 3D structures, while signs of hazes have been detected for some of them. Brown dwarfs usually lack a parent star, making their detection and characterization easier and making them the ideal playground to test our techniques for characterizing exoplanets in the future. Long temporal baseline, time-resolved observations of brown dwarfs suggest that these atmospheres are very dynamic with the observed light curves (and thus the clouds that shape them) changing shape within a single rotation. Observed spectra of brown dwarfs and some imaged exoplanets suggest that their atmospheres are in chemical disequilibrium: spectra of some cooler (Y and T) brown dwarfs lack strong NH3 lines predicted by equilibrium chemistry, while observations of some T dwarfs and imaged exoplanets show stronger CO lines than expected from equilibrium chemistry. These observations suggest that vertical mixing in these atmospheres leads to an overabundance of CO in comparison to CH4, and under-abundance of NH3.

In this talk I will present our current knowledge of clouds in brown dwarf atmospheres and discuss how we can use maps to place constraints on atmospheric dynamics. I will discuss what the first maps we currently have tell us about brown dwarf atmospheres in the L/T transition, and what they teach us about mapping imaged exoplanets in the JWST era. Finally, I will present the preliminary results of an update to the state-of-the-art radiative transfer code of Marley and Fortney, that can now model atmospheres in chemical disequilibrium.

JPL Contact: Max Millar-Blanchaer

About the Speaker
Theodora Karalidi is a postdoctoral researcher at UCSC. She earned her PhD from Leiden and SRON in the Netherlands, working on modeling the spectropolarimetric signals of terrestrial and giant exoplanets. She is interested in radiative transfer modeling of brown dwarf and exoplanet atmospheres and mapping them using observed light curves.


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