X-shooter observations of main-sequence stars in the globular cluster NGC 2808: First chemical tagging of a he-normal and a he-rich dwarf

  title={X-shooter observations of main-sequence stars in the globular cluster NGC 2808: First chemical tagging of a he-normal and a he-rich dwarf},
  author={Angela Bragaglia and Eugenio Carretta and Raffaele Gratton and Sara Lucatello and Antonino P. Milone and Giampaolo Piotto and Valentina D’Orazi and Santi Cassisi and Christopher Sneden and L. H. Rodriguez-Merino Inaf - Osservatorio Astr. di Bologna and INAF-Oss. Astron. Padova and Universit̀a di Padova and INAF-Oss. Astr. Collurania and Dept. of Physics Astronomy and McDonald Obs. STScI},
  journal={The Astrophysical Journal},
We present the first chemical composition study of two unevolved stars in the globular cluster NGC 2808, obtained with the X-shooter spectrograph at VLT. NGC 2808 shows three discrete, well-separated main sequences. The most accepted explanation for this phenomenon is that their stars have different helium contents. We observed one star on the bluest main sequence (bMS, claimed to have a high helium content, Y ~0.4) and the other on the reddest main sequence (rMS, consistent with a canonical… 

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