Li - O anti-correlation in NGC 6752: evidence for Li-enriched polluting gas - Astrophysics > Astrophysics of GalaxiesReport as inadecuate

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Abstract: Elemental correlations and anti-correlations are known to be present inglobular clusters GCs owing to pollution by CNO cycled gas. Because of itsfragility Li is destroyed at the temperature at which the CNO cycling occurs,and this makes Li a crucial study for the nature of the contaminating stars. Weobserved 112 un-evolved stars at the Turnoff of the NGC6752 cluster with FLAMESat the VLT to investigate the presence and the extent of a Li-O correlation.This correlation is expected if there is a simple pollution scenario. Li 670.8nm and O triplet 771 nm abundances are derived in NLTE. All stars belong toa very narrow region of the color-magnitude diagram, so they have similarstellar parameters Teff, log g. We find that O and Li correlate, with a highstatistical significance that confirms the early results for this cluster. Atfirst glance this is what is expected if a simple pollution of pristine gaswith CNO cycled gas O-poor, Li-poor occurred. The slope of the relationship,however, is about 0.4, and differs from unity by over 7 Sigma. A slope of oneis the value predicted for a pure contamination model. We confirm an extendedLi-O correlation in non evolved stars of NGC 6752. At the same time thecharacteristic of the correlation shows that a simple pollution scenario is notsufficient to explain the observations. Within this scenario the contaminantgas must have been enriched in Li. This would rule out massive stars as mainpolluters, and favor the hypothesis that the polluting gas was enriched byintermediate or high-mass AGB stars, unless the former can be shown to be ableto produce Li. According to our observations, the fraction of polluting gascontained in the stars observed is a considerable fraction of the stellar massof the cluster.

Author: Z.-X. Shen, P. Bonifacio, L. Pasquini, S. Zaggia


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