Planetary and exoplanetary Astronomy Lunch Seminar (PALS) for 2023-04-24

Series: Planetary and exoplanetary Astronomy Lunch Seminar (PALS)
Date: Monday 24-April-2023
Time: 11:15-12:15
Location: ATL 1250
Speaker: Callie Hood
Title: The Promise and Challenge of Brown Dwarf Retrievals at Medium Spectral Resolution

Abstract: Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Atmospheric retrieval approaches have been successfully applied to a number of low-resolution (R≈100) spectra of L, T, and Y dwarfs, yielding constraints on the abundances of chemical species and temperature structures of these atmospheres. Medium-resolution (R≈1E3) spectra of brown dwarfs offer significant additional insight, as molecular features are more easily disentangled from one another and the thermal structure of the upper atmosphere is more readily probed. First, I will discuss my recently submitted publication in which we apply a GPU-version of the CHIMERA retrieval framework to a high signal-to-noise, medium-resolution (R≈6000) FIRE spectrum of a T9 dwarf from 0.85-2.5 microns. At 60x higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise, which we explore. For example, we examine the strong effect of different line lists on our retrieved molecular abundances, in particular for CH4. We compare these retrieval results to those obtained for a R≈100 spectrum of the same object, revealing how constraints on atmospheric abundances improve by an order of magnitude or more (depending on the species) with increased spectral resolution. Next, I will present preliminary results from the application of this retrieval framework to JWST NIRSpec/G395H observations of a T8 dwarf with R~2700 over 2.87–5.14 microns. Together, these projects illustrate the power of retrievals on high-quality, medium-resolution spectra to precisely constrain the atmospheric properties of substellar atmospheres.

For further information contact PALS coordinators Quanzhi Ye at and Tad Komacek at


Special accommodations for individuals with disabilities can be made by calling (301) 405-3001. It would be appreciated if we are notified at least one week in advance.


Directions and information about parking can be found here.

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