摘要：The lowest-mass stars and substellar brown dwarfs are the most abundant populations in the Solar Neighborhood, with objects of mass ≤ 0.2 Msun comprising over half of all local stars (d ≤ 20 pc). These ultracool dwarfs are predominantly members of the Milky Way's thin disk population, and given their intrinsically faint luminosities and substellar thermal evolution questions remain as to whether they are as abundant in the metal-poor thick disk or halo populations, or among accreted extragalactic populations. Sensitive infrared imaging and spectroscopic surveys made possible by JWST and soon the Nancy Grace Roman Space Telescope are starting to provide the samples necessary to address these questions. In this talk, I will discuss the two ongoing JWST programs aimed at investigating these ancient populations of low-mass objects both in the Solar Neighborhood and deep extragalactic surveys. These programs have provided new insights into metal-dependent atmospheric chemistry, while revealing the samples of low mass stars and brown dwarfs at 1-10 kpc distances. I will conclude by summarizing the objectives of our Cycle 1 Roman program that aims to build the deepest and largest survey of ultracool dwarfs that will provide robust constraints on their Galactic distribution and ancient low-mass star formation.
简介：Adam Burgasser is a Professor of Astronomy & Astrophysics at UC San Diego in California, USA, where he directs the Cool Star Lab. He is an observational astrophysicist whose research focuses on the lowest-mass stars, brown dwarfs, and giant extrasolar planets. He is best known for leading the definition of the T dwarf spectral class, discoveries of metal-poor brown dwarfs, and work on characterizing planet-hosting stars such as TRAPPIST-1. Prof. Burgasser is also an education researcher who studies remote instruction and graduate education, and recently co-authored the book "How to Critically Read the Scientific Research Literature: Introducing the CERIC Method" with Dr. Genevive Bjorn. Prof. Burgasser is a Fellow and former Vice-President of the American Astronomical Society (AAS), a Fulbright Scholar, and is Vice Provost of UCSD's Muir College.
