Helium abundance difference within globular clusters: NGC 2808.

CACCIARI, C.; PASQUINI, L.; VALENTI, E.; KÄUFL, H. U.; MAUAS, P.J.D.

Memorie della Societa Astronomica Italiana

Societa Astronomica Italiana

Lugar: Trieste; Año: 2015 vol. 86 p. 207 - 210

Multiple populations have been recently detected in most Galacticglobular clusters, even with no significant spread in metallicity.Unusual features of the observed colour-magnitude diagrams can beexplained by differences in the He content of the stars belonging to thesub-populations. We report on empirical evidence of He abundance spreadin a few globular clusters, with particular attention to NGC 2808, whereHe abundance variation has been measured in a pair of otherwiseidentical red giant stars using the HeI 1083 nm line. A quantitativeestimate of this difference has been derived by appropriatechromospheric modelling, in very good agreement with stellar evolutionrequirements.Partly based on observations collected at ESO VLT (Chile), underprogramme 384.D-0283.