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Observational Signatures of the First Stars

At present, there are several feasible observational probes of the first stars in the universe. Here, we examine the constraints on early stellar activity from the metallicity of the high-redshift Ly-$α$ clouds, from the effects of stellar ionizing photons on reionization and the cosmic microwave background (CMB), and from the implications of gravitational microlensing results for the presence of stellar remnants in galactic halos. We also discuss whether the above signatures are consistent with each other, i.e., if they reflect the same population of stars.