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Ultracool Demography With a Volume-Limited Census of the Solar Neighborhood

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Title:Ultracool Demography With a Volume-Limited Census of the Solar Neighborhood
Authors:Best, William Marshall Jack
Contributors:Liu, Michael C. (advisor)
Magnier, Eugene A. (advisor)
Astronomy (department)
binary stars
brown dwarfs
initial mass function
show 3 moreL/T transition dwarfs
star formation
show less
Date Issued:Dec 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:As the lowest-mass objects created by star formation processes, brown dwarfs are essential to a complete understanding of the star and planet formation history of our galaxy. To this end, a complete volume-limited sample of brown dwarfs in the solar neighborhood is critical for testing formation theories. To create such a sample, we (1) searched for brown dwarfs missed in previous surveys to complete the census, and (2) measured precise trigonometric distances to define the sample. We conducted a wide-field (28,000 deg^2) search using the Pan-STARRS1 and WISE surveys, discovering the most L/T transition dwarfs of any search to date. We additionally discovered a binary brown dwarf with component masses ~4 M_Jup, the lowest-mass binary discovered to date, providing clear evidence that normal star-formation processes produce planetary-mass binaries. We measured parallaxes for 348 L and T dwarfs using the wide-field infrared camera WFCAM on the United Kingdom Infrared Telescope (UKIRT) to reach well beyond the red limit of Gaia, producing the largest single batch of parallaxes for brown dwarfs to date. We constructed a volume-limited sample of L0-T8 dwarfs out to 25 pc, covering two-thirds of the sky (declinations -30 to +60 deg) and containing 350 members, four times more than the previous most complete sample of L and T dwarfs. Our volume-limited sample of brown dwarfs is the first beyond 8 pc defined entirely by parallaxes. We identified a distinct gap in the J-K color at the L/T transition, implying a phase of rapid atmospheric evolution whose T_eff (~1300 K) is in tension with model predictions. Using synthetic populations tied to our volume-limited sample, we calculated the most precise brown dwarf space density and luminosity function to date, and we placed improved constraints on the substellar initial mass function and formation history. Our volume-limited sample will continue to be a rich source of empirical constraints for studies of local brown dwarfs.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018.
Pages/Duration:558 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Astronomy

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