A Systematic Data Driven Characterization of the Atmospheres of Brown Dwarfs: At the Boundary Between Stars and Planets

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Brown dwarfs are unusual objects in the galaxy. They straddle the boundary between stars and planets - too large to be called planets and too small to be stars. They are not massive enough to fuse hydrogen like stars. Also, their chemical composition often resembles giant gas planets like Jupiter. Studying them presents a great opportunity to learn about atmospheric physics in both stars and planets. This award funds work to study thousands of brown dwarfs using data from public archives. The researchers will update their atmospheric models, and test them with comparisons with their data. Their main database will be the SpeX Prism Spectral Library obtained with the NASA Infrared Telescope Facility. They will also draw conclusions about atmospheric physics based on a detailed statistical study of these brown dwarfs. The results will also be useful to interpreting observations of extrasolar planets. A graduate student and several undergraduate students will participate in the research, including minorities. The PI will work with the Society for Advancement of Chicanos/Hispanics and Native Americans in Science (SACNAS) to increase the numbers of Hispanics and Native Americans in science. The team will apply Bayesian atmospheric retrieval techniques, widely employed in the extrasolar planet community, to a large sample of brown dwarfs. These tools will be used to determine cloud properties and thermal structures and chemistries across a broad range of temperatures and gravities. In particular, they will address outstanding brown dwarf issues such as the behavior of clouds across the low mass L-T transition, the evolution of disequilibrium chemistry with temperature, and the first measure of the distribution of metallicities and carbon-to-oxygen ratios with the populations. First, they will upgrade their models to include high-temperature opacities and different thermal profiles. Next, they will apply their analysis across the entire SpeX database and explore the relationships between temperature, cloud properties, and molecular abundances and publish results. Ultimately, they will finish retrieval analysis on all SpeX objects and apply to other available datasets for brown dwarfs.