Our FLAMES survey of Na-O anticorrelation in globular clusters ( GCs ) is extended to NGC 4833 , a metal-poor GC with a long blue tail on the horizontal branch ( HB ) .
We present the abundance analysis for a large sample of 78 red giants based on UVES and GIRAFFE spectra acquired at the ESO-VLT .
We derived abundances of Na , O , Mg , Al , Si , Ca , Sc , Ti , V , Cr , Mn , Fe , Co , Ni , Cu , Zn , Y , Ba , La , Nd .
This is the first extensive study of this cluster from high resolution spectroscopy .
On the scale of our survey , the metallicity of NGC 4833 is [ Fe/H ] = -2.015 \pm 0.004 \pm 0.084 dex ( rms = 0.014 dex ) from 12 stars observed with UVES , where the first error is from statistics and the second one refers to the systematic effects .
The iron abundance in NGC 4833 is homogeneous at better than 6 % .
On the other hand , the light elements involved in proton-capture reactions at high temperature show the large star-to-star variations observed in almost all GCs studied so far .
The Na-O anticorrelation in NGC 4833 is quite extended , as expected from the high temperatures reached by stars on the HB , and NGC 4833 contains a conspicuous fraction of stars with extreme [ O/Na ] ratios .
More striking is the finding that large star-to-star variations are seen also for Mg , which spans a range of more than 0.5 dex in this GC .
Depletions in Mg are correlated to the abundances of O and anti-correlated with Na , Al , and Si abundances .
This pattern suggests the action of nuclear processing at unusually high temperatures , producing the extreme chemistry observed in the stellar generations of NGC 4833 .
This extreme changes are also seen in giants of the much more massive GCs M 54 and \omega Cen , and our conclusion is that NGC 4833 has probably lost a conpicuous fraction of its original mass due to bulge shocking , as also indicated by its orbit .