Browsing by Author "Alves, Sanzia"
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- ItemHelium enhancement among horizontal-branch stars and the near-UV color-magnitude diagrams(2015) Valcarce, Aldo A. R.; Catelan, Márcio; Alonso-García, Javier; Contreras Ramos, Rodrigo; Alves, SanziaThe distribution of horizontal branch stars in globular cluster color-magnitude diagrams is a sensitive probe of their original helium abundances. In this sense, they have been extensively used recently as indicators of possible variations in the helium content Y among the different populations of stars within individual globular clusters. However, recent analyses based on visual and near-ultraviolet color-magnitude diagrams have provided conflicting results. In order to clarify the situation, in this presentation we discuss the optimum ranges of applicability of this “HB Y test” in different filter systems, in terms of the temperature range covered by the horizontal branch stars. In particular, we discuss the case of M3 (NGC 5272), based on multi-band photometry (HST, Strömgren, Johnson), thus setting new and tight constraints on the internal range in Y within this cluster. We also provide an application of this "HB Y test" to other selected clusters....
- ItemMultiple populations in M3: chemical abundances in AGB stars(2015) Alves, Sanzia; Contreras Ramos, Rodrigo; Amigo, Pia; Valcarce, Aldo A. R.; Cortés, Cristian; Hajdu, Gergely; Jurcsik, Johanna; Zoccali, Manuela; Catelan, MárcioSince the discovery of multiple populations in globular clusters, it is widely accepted that most globulars have at least two populations that can be classified in terms of their Na abundance, with the Na-poor stars belonging to the first stellar population, and the Na-rich stars to a second population. In the case of NGC 6752, it has been found that all the Na-rich stars fail to reach the asymptotic giant branch (AGB) phase, thus suggesting that the second-generation stars in this cluster all become so-called AGB-manqué stars after a hot horizontal branch (HB) phase. In contrast, stars belonging to both populations are present on the AGB phase in 47 Tucanae, which is consistent with the lack of a sizeable population of very hot HB stars in this cluster. In this contribution, we use high-resolution spectra obtained with UVES@VLT to analyze the chemical behavior of AGB stars in M3 (NGC 5272), a globular cluster with an HB morphology intermediate between those of NGC 6752 and 47 Tuc, to check whether second-generation stars in this cluster undergo an AGB-manqué phase as in NGC 6752, or whether instead they are able to successfully reach the AGB, as seen in 47 Tuc....