We present an abundance analysis of 96 horizontal branch ( HB ) stars in NGC 2808 , a globular cluster exhibiting a complex multiple stellar population pattern .
These stars are distributed in different portions of the HB and cover a wide range of temperature .
By studying the chemical abundances of this sample , we explore the connection between HB morphology and the chemical enrichment history of multiple stellar populations .
For stars lying on the red HB , we use GIRAFFE and UVES spectra to determine Na , Mg , Si , Ca , Sc , Ti , Cr , Mn , Fe , Ni , Zn , Y , Ba , and Nd abundances .
For colder , blue HB stars , we derive abundances for Na , primarily from GIRAFFE spectra .
We were also able to measure direct NLTE He abundances for a subset of these blue HB stars with temperature higher than \sim 9000 K. Our results show that : ( i ) HB stars in NGC 2808 show different content in Na depending on their position in the color-magnitude diagram , with blue HB stars having higher Na than red HB stars ; ( ii ) the red HB is not consistent with an uniform chemical abundance , with slightly warmer stars exhibiting a statistically significant higher Na content ; and ( iii ) our subsample of blue HB stars with He abundances shows evidence of enhancement with respect to the predicted primordial He content by \Delta Y = +0.09 \pm 0.01 .
Our results strongly support theoretical models that predict He enhancement among second generation ( s ) stars in globular clusters and provide observational constraints on the second-parameter governing HB morphology .