Mg isotopic abundance ratios are measured in 20 bright red giants in globular cluster NGC 6752 based on very high-resolution ( R \sim 110,000 ) , high signal-to-noise spectra obtained with UVES on the VLT .
There is a considerable spread in the ratio ^ { 24 } Mg : ^ { 25 } Mg : ^ { 26 } Mg with values ranging from 53:9:39 to 83:10:7 .
We measured the abundances 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 and exhibit the usual anticorrelations between O-Na and Mg-Al .
A positive correlation is found between ^ { 26 } Mg and Al , a mild anticorrelation is found between ^ { 24 } Mg and Al , while no correlation is found between ^ { 25 } Mg and Al .
None of the elemental or isotopic abundances show a dependence on evolutionary status and , as shown by Gratton et al .
( 2001 ) , the abundance variations exist even in main sequence stars .
This strongly suggests that the star-to-star abundance variations are a result of varying degrees of pollution with intermediate mass AGB stars being likely polluters .
Consideration of the extremes of the abundance variations provides the composition of the ambient material and the processed material .
In the least contaminated stars ( lowest Na and Al and highest O and Mg abundances ) , we infer a Mg isotopic ratio around 80:10:10 and a composition ( [ O/Fe ] , [ Na/Fe ] , [ Mg/Fe ] , [ Al/Fe ] ) \simeq ( 0.6 , - 0.1 , 0.5 , 0.0 ) .
In the most polluted stars , we find a Mg isotopic ratio around 60:10:30 and a composition ( [ O/Fe ] , [ Na/Fe ] , [ Mg/Fe ] , [ Al/Fe ] ) \simeq ( - 0.1 , 0.6 , 0.3 , 1.2 ) .
Even for the least polluted stars , the abundances of ^ { 25 } Mg and ^ { 26 } Mg relative to ^ { 24 } Mg are considerably higher than predicted for ejecta from Z = 0 supernovae .
Zero metallicity AGB stars may be responsible for these higher abundances .
Our measured Mg isotopic ratios reveal another layer to the globular cluster star-to-star abundance variations that demands extensions of our present theoretical knowledge of stellar nucleosynthesis by giant stars .