Context :

Aims : We present an analysis of FLAMES-Giraffe spectra for several bright giants in NGC 6441 , to investigate the presence and extent of the Na-O anticorrelation in this anomalous globular cluster .

Methods : The field of NGC 6441 is very crowded , with severe contamination by foreground ( mainly bulge ) field stars .
Appropriate membership criteria were devised to identify a group of 25 likely cluster members among the about 130 stars observed .
Combined with the UVES data obtained with the same observations ( Gratton et al .
2006 ) , high dispersion abundance analyses are now available for a total of 30 stars in NGC 6441 , 29 of them having data for both O and Na .
The spectra were analyzed by a standard line analysis procedure ; care was taken to minimize the impact of the differential interstellar reddening throughout the cluster , and to extract reliable information from crowded , and moderately high S/N ( 30-70 ) , moderately high resolution ( R \sim 23 , 000 ) spectra .

Results : NGC 6441 has the typical abundance pattern seen in several other globular clusters .
It is very metal-rich ( [ Fe/H ] = -0.34 \pm 0.02 \pm 0.04 dex ) .
There is no clear sign of star-to-star scatter in the Fe-peak elements .
The \alpha - elements Mg , Si , Ca , and Ti are overabundant by rather large factors , suggesting that the cluster formed from material enriched by massive core collapse SNe .
The O-Na anticorrelation is well defined , with about 1/4 of the stars being Na-rich and O-poor .
One of the stars is a Ba-rich and moderately C-rich star .
Such stars are rare in globular clusters .

Conclusions : The distribution of [ Na/O ] ratios among RGB stars in NGC 6441 appears similar to the distribution of colors of stars along the horizontal branch .
The fraction of Na-poor , O-rich stars found in NGC 6441 agrees well with that of stars on the red horizontal branch of this cluster ( in both cases about 80 % ) , with a sloping distribution toward lower values of [ O/Na ] ( among RGB stars ) and bluer colors ( among HB stars ) .