COBE CONSTRAINTS ON BARYON ISOCURVATURE MODELS

We consider Bayesian constraints on standard isocurvature baryon model s from the slope and normalization of the anisotropy power spectrum de tected by the COBE DMR experiment in their 2 year maps. In conjunction with either the amplitude of matter fluctuations sigma(8) or its slop e, all open models are ruled out at greater than 95% confidence, where as cosmological-constant dominated models are constrained to be highly ionized. By including the COBE FIRAS 95% confidence upper limit on sp ectral distortion under the assumption of collisional ionization, we f urther reduce the available parameter space for Lambda models by exclu ding these highly ionized models. These constraints define a single re maining class of standard models which makes definite and testable pre dictions for degree-scale anisotropies and large-scale structure.