Program: GN-2020B-Q-321

All very-low-mass objects ever formed still exist. The cold Jupiter-mass field brown dwarfs (BDs) therefore constrain models of star formation and of BD evolution, they also act as proxies for exoplanet studies. For these reasons the coldest BDs are high priority targets for JWST. 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. They have been discovered in the WISE mid-IR imaging survey, but confirmation and characterization (pre-JWST) requires near-IR data. In 2019, only 12 BDs cooler than 400K were known. In 2020 Meisner et al. and Bardalez Gagliuffi et al. published new candidate cold BDs from reanalyses of WISE data. In 20A we obtained J-band photometry of 3 of the new BDs using Gemini DD and FT time, we determined temperatures of 350K, 375K and 425K. Sixteen new BDs with mid-IR colors implying T<400K remain unclassified. We request time to obtain J photometry of 15 of these, accessible at Gemini in 20B. This work may double the number of T<400K BDs known, these are fundamentally important objects, with masses of 3-15 Jupiters, and atmospheres cold enough for water clouds to form. It is vital to characterize these objects now, so that JWST resources can be optimally used.