NGC 6388 reloaded: some like it hot, but not too much. New constraints on the first-generation polluters

Abstract

Multiple stellar populations in globular clusters (GCs) are defined and recognized by their chemical signature. Second-generation stars show the effects of nucleosynthesis in the more massive stars of the earliest component that formed in the first star formation burst. High-temperature H-burning produces the whole pattern of (anti-) correlations in proton-capture elements that are widely found in GCs. However, it is still debated where this burning occurred. Here we introduce new powerful diagnostic plots to detect evidence (if any) of products from proton-capture reactions that occur at very high temperatures. To test these detectors of high-temperature H-burning plots, we show that stringent constraints can be placed on the temperature range of the first-generation polluters that contributed to shaping the chemistry of multiple stellar population in the massive bulge GC NGC 6388. Using the largest sample to date (185 stars) of giants with detailed abundance ratios in a single GC (except ω Cen), we may infer that the central temperature of part of the polluters must have been comprised between ∼100 and ∼150 MK if we consider hydrostatic H-burning in the core of massive stars. A much more narrow range (110−120 MK) is inferred if the polluters can be identified in massive asymptotic giant branch stars.