1996A&A...313..129B

Sub-arcsec B and V images of the central 2.5arcmin of the post-core-collapse globular cluster M 30 are used to study the stellar populations lying in the central parts of this cluster and to analyze the influence of the stellar content on the radial color gradient reported for this cluster. We find a populated blue horizontal branch which follows a flat radial distribution. The red giants (defined as the objects above the horizontal branch in this paper) are found to be depleted relatively to the other bright detected stellar populations. A highly concentrated population of 42 blue stragglers has also been detected. The presence of a B-V color gradient (0.20-0.24mag/dex) is confirmed. A blueing is detectable from the cluster center out to the edge of the images at r≃1arcmin. None of the detected bright stellar populations (red giant branch, horizontal branch, asymptotic giant branch and blue straggler stars) is found to be at the origin of this gradient. This result suggests that the stellar population(s) responsible for this gradient has still to be identified. Some plausible candidates are tentatively proposed in this paper.