Recent work, based on data from the Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs), has revealed that all the analysed clusters host two groups of first- (1G) and second-generation (2G) stars. In most GCs, both 1G and 2G stars host substellar populations with different chemical composition. We compare multiwavelength HST photometry with synthetic spectra to determine for the first time the average helium difference between the 2G and 1G stars in a large sample of 57 GCs and the maximum helium variation within each of them. We find that in all clusters 2G stars are consistent with being enhanced in helium with respect to 1G. The maximum helium variation ranges from less than 0.01 to more than 0.10 in heliummass fraction and correlateswith both the clustermass and the colour extension of the horizontal branch (HB). These findings demonstrate that the internal helium variation is one of the main (second) parameters governing the HB morphology.
Milone, A.P., Marino, A.F., Renzini, A., D'Antona, F., Anderson, J., Barbuy, B., et al. (2018). The Hubble Space Telescope UV legacy survey of galactic globular clusters - XVI. The helium abundance of multiple populations. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 481(4), 5098-5122 [10.1093/MNRAS/STY2573].
The Hubble Space Telescope UV legacy survey of galactic globular clusters - XVI. The helium abundance of multiple populations
Tailo M.;
2018
Abstract
Recent work, based on data from the Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs), has revealed that all the analysed clusters host two groups of first- (1G) and second-generation (2G) stars. In most GCs, both 1G and 2G stars host substellar populations with different chemical composition. We compare multiwavelength HST photometry with synthetic spectra to determine for the first time the average helium difference between the 2G and 1G stars in a large sample of 57 GCs and the maximum helium variation within each of them. We find that in all clusters 2G stars are consistent with being enhanced in helium with respect to 1G. The maximum helium variation ranges from less than 0.01 to more than 0.10 in heliummass fraction and correlateswith both the clustermass and the colour extension of the horizontal branch (HB). These findings demonstrate that the internal helium variation is one of the main (second) parameters governing the HB morphology.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
