One of the open question in the current planetary science is the formation process of gas giant planets. To unveil the origin of giant planets, planetary atmospheric compositions have been proposed as a powerful tool to diagnose where and how the gas giant formed. Particularly atmospheric nitrogen provides valuable insights on the planet formation process. As the bulk nitrogen abundance of a giant planet is estimated by observed NH3, to establish the empirical calibration on the ratio of the observable NH3 to bulk N abundances (fNH3/fN) is important. Here we propose IRCS+LGS Echelle spectroscopy at J-band with a spectral resolution of R=5,000 for three cool brown dwarf binaries with 400 <∼ Teff <∼ 700. The advantage of observing binary system is that they likely share the same atmospheric elemental abundances and thus isolate the effects of Teff and log g from [Fe/H] on the observable NH3 abundance. We will investigate the fNH3/fN relation of self-luminous objects with a multiple different methods (comparison with pre-computed grid, retrieval, cross-correlation) to avoid model-dependent interpretation. Our observations will provide an important calibration to characterize directly imaging planets with atmospheric nitrogen in the JWST era.
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