Exploring the coldest observed extrasolar atmospheres with JWST

This project will focus on using Brewster to understand the conditions in the atmospheres of extremely cool Y dwarfs that will be observed by JWST in Cycle 1. Y dwarfs span the temperature range from 250K up to around 500K, and represent the coldest directly observed atmospheres beyond the solar system. Their masses overlap with the planetary regime, and the population may include examples of ejected planets. The coldest examples are expected to show evidence of water clouds in their spectra, whist warmer examples may show exotic clouds formed from halides or alkali sulphides. Due to their cool temperatures, Y dwarfs are extremely faint at near-infrared wavelengths, and are essentially invisible at optical wavelengths. Since their discovery in 2011 it has only been possible to obtain relatively poor quality near-infrared spectra using Hubble. JWST will provide the first high quality spectroscopy across the wavelengths where they emit most of their light, which will revolutionise our understanding of these objects. By using Brewster to analyse JWST spectroscopy of these objects this project will provide the insights to their clouds, chemistry and thermal structure.