Abundances in giant stars of the globular cluster NGC 6752

摘要: Recent theoretical yields and chemical evolution models demonstrate that intermediate-mass AGB stars cannot reproduce the observed abundance distributions of O, Na, Mg, Al. As a further observational test of this finding, we present elemental ratios [X/Fe] for 20 elements in 38 bright giants globular cluster NGC 6752 based on high-resolution, high signal-to-noise spectra obtained with UVES VLT. This is most complete spectroscopic analysis terms number considered stars sample. The span more than 1000 K effective temperature than 3 visual magnitudes along red giant branch. None ratios [X/Fe] show correlation evolutionary status. For Si heavier elements, small scatter may be attributable to measurement uncertainties. Our mean are good agreement previous studies also consistent other clusters field at same metallicity. [Ba/Eu] [La/Eu] exhibit values, metallicity, lie approximately midway between pure r -process solar ( s + -process) mix, indicating have played role proto-cluster gas. 
For first time, find possible evidence an variation than Al cluster. We between [Si/Fe] and [Al/Fe] which anomalies being synthesized via proton captures temperatures. Leakage from Mg-Al chain into  28 explain excess highest [Al/Fe]. identify correlations between [Y/Fe] and [Al/Fe], [Zr/Fe] and [Ba/Fe] suggesting that Y, Zr, Ba abundances increase by about 0.1 dex as Al increases about 1.3 dex. While statistically significant, amplitudes variations small. If in Y, and Ba indeed real, then synthesis Al anomalies must taken place within unknown class ran -process.