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We present an abundance analysis of 96 horizontal branch (HB) stars inNGC2808, a globular cluster exhibiting a complex multiple stellar populationpattern. These stars are distributed in different portions of the HB and covera wide range of temperature. By studying the chemical abundances of thissample, we explore the connection between HB morphology and the chemicalenrichment history of multiple stellar populations. For stars lying on the redHB, 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 deriveabundances for Na, primarily from GIRAFFE spectra. We were also able to measuredirect NLTE He abundances for a subset of these blue HB stars with temperaturehigher than ~9000 K. Our results show that: (i) HB stars in NGC2808 showdifferent content in Na depending on their position in the color-magnitudediagram, with blue HB stars having higher Na than red HB stars; (ii) the red HBis not consistent with an uniform chemical abundance, with slightly warmerstars exhibiting a statistically significant higher Na content; and (iii) oursubsample of blue HB stars with He abundances shows evidence of enhancementwith respect to the predicted primordial He content by Delta(Y)=+0.09+-0.01.Our results strongly support theoretical models that predict He enhancementamong second generation(s) stars in globular clusters and provide observationalconstraints on the second-parameter governing HB morphology.

Helium enhanced stars and multiple populations along the horizontal branch of NGC2808: direct spectroscopic measurements