Browsing by Author "Sweigart, Allen V."
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- ItemDisentangling multiple stellar populations in globular clusters using the Strömgren system(2015) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.An increasing amount of spectroscopic and photometric evidence is showing that the stellar populations of globular clusters are not as simple as they have been considered for many years. The presence of at least two different populations of stars is being discovered in a growing number of globular clusters, both in our Galaxy and in others. We have started a series of observations of Galactic globular clusters using the Strömgren photometric system in order to find the signatures of these multiple populations and establish their presence in a more complete sample of globular clusters in the Milky Way, and to study their radial distributions and extensions. We present here the first results of our survey....
- ItemEffects of Helium Enrichment in Globular Cluster Populations(2011) Valcarce, Aldo A. R.; Catelan, Márcio; Sweigart, Allen V.Recently, the understanding of globular clusters (GCs) has drastically changed owing to the improvement in spectroscopic and photometric observations, which have shown that not all GCs could be considered simple stellar populations. Whilst spectroscopic studies have shown variations of some light elements in different degrees in all observed GCs (e.g., O-Na anticorrelation, Carretta et al. 2009), photometric studies have shown splits in some phases of color-magnitude diagrams (CMDs), where the triple main sequence (MS) detected in NGC 2808 has been attributed to differences in the helium abundance (ΔY, Piotto et al. 2007), which cannot be measured with enough precision in GCs. In this contribution, we show the other effects that must be observed in CMDs of GCs if ΔY is real....
- ItemErratum: "Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388" [Astron. J. 124, 949 (2002)](2003) Pritzl, Barton J.; Smith, Horace A.; Catelan, Márcio; Sweigart, Allen V.In Tables 4 and 5, we inadvertently listed Modified Heliocentric Julian Dates instead of ordinary Heliocentric Julian Dates as indicated in the table headings. To make the listed dates match the table headings, 0.5 should be added to the listed dates. Corrected tables with ordinary Heliocentric Julian Dates are given below. We thank Christine Clement, who noticed this error and brought it to our attention....
- ItemGlobular clusters as laboratories for stellar evolution(2010) Catelan, Márcio; Valcarce, Aldo A. R.; Sweigart, Allen V.Globular clusters have long been considered the closest approximation to a physicist's laboratory in astrophysics, and as such a near-ideal laboratory for (low-mass) stellar evolution. However, recent observations have cast a shadow on this long-standing paradigm, suggesting the presence of multiple populations with widely different abundance patterns, and—crucially- with widely different helium abundances as well. In this review we discuss which features of the Hertzsprung-Russel diagram may be used as helium-abundance indicators, and present an overview of available constraints on the helium abundance in globular clusters....
- ItemMultiple populations in Galactic globular clusters from a Strömgren perspective(2014) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.Our view of the stellar populations in globular clusters has radically changed in the last years. Now we are coming to believe that all globular clusters host at least two distinct stellar populations. We present in this contribution preliminary results of a photometric survey we are currently conducting to disentangle photometrically the several populations in a significant number of Galactic globular clusters, using the Strömgren system, aiming to characterize their relative ratios and their radial distributions....
- ItemMultiple populations in Galactic globular clusters: a survey in the Strömgren system(2013) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.We are coming to believe that stellar populations in globular clusters are not as simple as they were once thought to be. A growing amount of photometric and spectroscopic evidence shows that globular clusters host at least two different stellar populations. In our contribution to these proceedings we present the first results of a survey we are conducting to look for the presence of multiple populations in a significant number of Galactic globular clusters, using the Strömgren system. We intend to photometrically separate these populations and characterize their radial distributions and extensions....
- ItemVariable Stars in Metal-Rich Globular Clusters: NGC 6304 and NGC 6569(2002) Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.It has recently become evident that the RR Lyrae in metal-rich globular clusters ([Fe/H]> -1.0) have properties different from those of metal-rich RR Lyrae found in the field. In particular, they have longer periods than field RR Lyrae of similar metallicities, implying that the cluster RR Lyrae are more luminous than their field counterparts. Because RR Lyrae stars are major Population II standard candles, this finding has consequences for the ages of globular clusters and the galactic and extragalactic distance scales. We propose observations with the YALO telescope to obtain B,V CCD photometry of the RR Lyrae in the metal-rich globular clusters NGC 6304 and NGC 6569. These data will be used to obtain accurate periods and light curves for the RR Lyrae and will be compared to those in other systems to determine their relative luminosities. Direct comparisons will also be made to the other metal-rich globular clusters known to contain RR Lyrae.