STELLAR POPULATION AND COLOR GRADIENTS IN THE POST-CORE-COLLAPSE GLOBULAR-CLUSTER M-30 (NGC-7099)

Sub-arcsec B and V images of the central 2.5 arcmin of the post-core-c ollapse globular cluster M 30 are used to study the stellar population s lying in the central parts of this cluster and to analyze the influe nce of the stellar content on the radial color gradient reported for t his cluster. We find a populated blue horizontal branch which follows a flat radial distribution. The red giants (defined as the objects abo ve the horizontal branch in this paper) are found to be depleted relat ively to the other bright detected stellar populations. A highly conce ntrated population of 42 blue stragglers has also been detected.The pr esence of a B-V color gradient (0.20-0.24 mag/dex) is confirmed. A blu eing is detectable from the cluster center out to the edge of the imag es at r approximate to 1 arcmin. None of the detected bright stellar p opulations (red giant branch, horizontal branch, asymptotic giant bran ch and blue straggler stars) is found to be at the origin of this grad ient. This result suggests that the stellar population(s) responsible for this gradient has still to be identified. Some plausible candidate s are tentatively proposed in this paper.