Program: GN-2021A-FT-206

Brown Dwarfs (BDs) have insufficient mass for stable fusion, and they cool with time. They form the low-mass tail of the stellar mass function, and bridge the gap in mass between the solar system giant planets and cold dwarf stars. The cold, few-Jupiter-mass, BDs in the solar neighborhood constrain models of star formation and of BD evolution, they also act as proxies for exoplanet studies. Cold BDs are bright at 4.5um and faint at most other wavelengths due to strong absorption by water, methane and ammonia in their atmospheres. Recent deep searches of the WISE mid-IR sky survey have found candidate very cold BDs. Here we request time to obtain J-band photometry of three of the six candidate 350K BDs known that have 3.6um and 4.5um photometry but no near-IR data. Our group has demonstrated that the J, [3.6] and [4.5] colors constrain both temperature and metallicity of a BD. The proposed observations have the potential to increase the number of < 350K BDs known by 50%, a less dramatic result of an increase of 20% in each of the 340, 380, and 420K BD populations is also important, and is key to understanding the local very-low-mass population. For the typical age of the local field, these temperatures correspond to masses of 5, 8, and 10 Jupiter-masses. If confirmed to be cold, the BDs will be prime targets for JWST. The results will either be incorporated into a paper under review, or form a follow-up paper.