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Mg isotopic abundance ratios are measured in 20 bright red giants in globularcluster NGC 6752 based on very high-resolution, high signal-to-noise spectraobtained with UVES on the VLT. There is a considerable spread in the ratio24Mg:25Mg:26Mg with values ranging from 53:9:39 to 83:10:7. We measured theabundances of O, Na, Mg, Al, and Fe combining our sample with 21 RGB bump stars(Grundahl et al. 2002). The abundances of the samples are consistent andexhibit the usual anticorrelations between O-Na and Mg-Al. A positivecorrelation is found between 26Mg and Al, a mild anticorrelation is foundbetween 24Mg and Al, while no correlation is found between 25Mg and Al. None ofthe elemental or isotopic abundances show a dependence on evolutionary statusand, as shown by Gratton et al. (2001), the abundance variations exist even inmain sequence stars. This strongly suggests that the star-to-star abundancevariations are a result of varying degrees of pollution with intermediate massAGB stars being likely polluters. Even for the least polluted stars, theabundances of 25Mg and 26Mg relative to 24Mg are considerably higher thanpredicted for ejecta from Z=0 supernovae. Zero metallicity AGB stars may beresponsible for these higher abundances. Our measured Mg isotopic ratios revealanother layer to the globular cluster star-to-star abundance variations thatdemands extensions of our present theoretical knowledge of stellarnucleosynthesis by giant stars.Comment: Accepted for publication in A&

Mg isotopic ratios in giant stars of the globular cluster NGC 6752