Effective Temperature and Surface Gravity Degeneracy in Brown Dwarf Spectral Fitting

This paper computes the degeneracy between effective temperature and surface gravity in fitting brown dwarf spectra, a systematic that affects nearly every derived property. A hotter, higher-gravity atmosphere can mimic a cooler, lower-gravity one over a limited wavelength range, biasing inferred temperatures. The headline computed values are: bias_half_dex = 90; bias_1200_logg45 = -90; valley_slope_K_per_dex = 180. All values were obtained from the stated scalings and normalisations in the deposited code; this study is simulated and computed, not measured, and no new observations are reported. Where the framework supplies no value for a quantity the question requires, that absence is reported plainly as a negative result.