Browsing by Author "Kunder, Andrea"

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    G2C2-IV.A novel approach to study the radial distributions of multiple populations in Galactic globular clusters
    (OXFORD UNIV PRESS, 2015) Vanderbeke, Joachim; De Propris, Roberto; De Rijcke, Sven; Baes, Maarten; West, Michael; Alonso Garcia, Javier; Kunder, Andrea
    We use the horizontal branch (HB) morphology of 48 Galactic globular clusters (GCs) to study the radial distributions of the different stellar populations known to exist in GCs. Assuming that the (extremely) blue HB stars correspond to stars enriched in helium and light elements, we compare the radial distributions of stars selected according to colour on the HB to trace the distribution of the secondary stellar populations in GCs. Unlike other cases, our data show that the populations are well mixed in 80 per cent of the cases studied. This provides some constraints on the mechanisms proposed to pollute the interstellar medium in young GCs.
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    RR Lyrae in the LMC: Insights Into the Oosterhoff Phenomenon
    (2013) Kuehn, Charles A; Smith, Horace A.; Catelan, Marcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Dame, Kyra; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura
    Although more than eight decades have passed since P. Th. Oosterhoff drew attention to differences in the properties of RR Lyrae variables in globular clusters, the origin and significance of the Oosterhoff groups remain unclear. Nonetheless, the accumulation of extensive new observations of RR Lyrae stars in globular clusters of the Milky Way and Local Group galaxies allows a fresh look at the phenomenon. Insights come not only from surveys of variables within the original Oosterhoff groups I and II but also from recent observations of the Oosterhoff-intermediate systems found especially in smaller Local Group galaxies. We will compare properties of RR Lyrae in several systems to investigate what they reveal about system-to-system differences of transition temperature between fundamental-mode and first overtone pulsators and of horizontal branch luminosity. Both transition temperature and horizontal branch luminosity have at various times been credited as playing roles in the creation of the Oosterhoff dichotomy....
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    RR Lyrae Variables in NGC 2808
    (2011) Kunder, Andrea; Stetson, Peter B.; Catelan, Marcio; Amigo, Pía; de Propris, Roberto
    NGC 2808 is a unique globular cluster with not only a bimodal-horizontal branch (HB) but also with gaps on the blue horizontal branch. Adequate interpretation of the nature of the detected peculiarities in "bimodal" and "gap" clusters is of paramount importance for understanding the nature of the second parameter phenomenon and scenarios for the formation of the Galaxy. Although RR Lyrae variables are HB stars that can provide powerful constraints to models on the origin of bimodal HBs, unfortunately, until recently, only one RR Lyrae variable was known in this cluster. Here we present the first calibrated time-series CCD photometry for newly discovered fundamental mode RR Lyrae variables in NGC 2808, with observations over a range of twenty years. Investigations of RR Lyrae variable stars in this peculiar, bimodal-horizontal branch globular cluster are carried out to account for its formation, and the effects of helium enrichment and differential reddening. The Oosterhoff classification of NGC 2808, which has recently been associated with a previously unknown dwarf galaxy in Canis Major, is also discussed....