  We present an abundance analysis of 96 horizontal branch (HB) stars in
NGC2808, 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 ~9000 K. Our results show that: (i) HB stars in NGC2808 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+-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.
