Fundamental parameters for M4, the nearest globular cluster

Several fundamental parameters for M4 remain poorly determined, even though it is the closest globular cluster to the Sun. There is wide scatter in estimates of the reddening, metallicity and distance modulus, as presented in the literature. By reworking many of the published data on the assumption that |R[ = AV/E(B-V)] ~ 4| rather than ~ 3, it is shown that consistent values for each of these parameters can be derived. The initial assumption R ~ 4 is justified further, and a value of |E(B-V) = 0.37 ± 0.01| mag is found. The metallicity and distance modulus are then |[Fe/H] = -1.1 ± 0.25 and (m-M)₀ = 11.22 ± 0.11| mag respectively.