A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late T-dwarfs

Abstract

abstract: The spectra of brown dwarfs are key to exploring the chemistry and physics thattake place in their atmospheres. Late T dwarf (950 - 500 K) spectra are particularly\ndiagnostic due to their relatively cloud free atmospheres and deep molecular\nbands. With the use of powerful atmospheric retrieval tools, these properties permit\nconstraints on molecular/atomic abundances and temperature profiles. Building\nupon previous analyses on T and Y dwarfs (Line et al. 2017; Zalesky et al. 2019),\nI present a uniform retrieval analysis of 50 T dwarfs via their low-resolution near infrared\nspectra. This analysis more than doubles the sample of T dwarfs with retrieved\nproperties. I present updates on current compositional trends and thermal\nprofile constraints amongst the T dwarf population. My analysis shows that my collection\nof objects form trends that are consistent with solar grid model expectations\nfor water, ammonia, methane, and potassium. I also establish a consistency between\nthe thermal structures of my objects with those of grid models. Moreover, I explore\nthe origin of gravity-metallicity discrepancies that are observed in some of my brown\ndwarf candidates.