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We have proprietary wide-field DECam (mounted on the 4m-Blanco telescope, NOAO) observations that cover the entire extent of NGC2808 and so will enable us to characterize the spatial distribution of the main-sequence (and red-giant, and horizontal branch) stars from the core to the tidal radius and obtain a clear picture of the evolutionary history of the cluster. The observations will then be compared to numerical simulations performed by our collaborators to characterize the formation and evolutionary history of this complex cluster.
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Fig. 1: Left - HST F814W, F475W - F814W color-magnitude diagram of NGC2808 from Milone et al. (2012a2012, A&A, 537, A77). Right - Hess diagram for the MS region (indicated with a grey box on the left). The three main sequences, blue, intermediate and red, are clearly separated from about the cluster turn-off level at F814W ~ 18.5 down to 22 mag.
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Fig. 2: DECam g-i vs u-r vs r color-color-magnitude diagram of Omega Cen member (multiple color dots) and field stars (gray dots) seen from the front (left panel) and the back (right). This approach can be applied to separate field and cluster stars thanks to the opportunity to use the u filter, since this band allows a better sensitivity to both effective temperature and metallicity. We will apply this method to separate cluster and field stars in NGC2808. This figure is taken from Calamida et al. (2017, AJ, 153, 175)).
Fig. 3: Left: DECam g, g-i color-magnitude diagram of Omega Cen member stars. Right: Zoom of the g, g-i color-magnitude diagram showing the split of Omega Cen main-sequence. It was previously identified only with HST and VLT photometry of the central regions of the cluster. We will identify the different main sequences in NGC2808 by using our DECam data for this cluster. This figure is taken from Calamida et al. (2017, AJ, 153, 175).
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Fig. 4: DECam footprint (blue) centered on NGC2808. The yellow square indicates the field of view of the ground-based + HST photometric catalog used in the study of Iannicola et al. (2009, ApJ, 696, L120). We will combine these datasets to DECam photometry to study the property of the different multiple populations across NGC2808.
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DECam data will be reduced by the student, in collaboration with the PI, Dr. Annalisa Calamida (STScI) and , Dr. Armin Rest (STScI, JHU), and the grad student Giovanni Strampelli (STScI, IAC), using our available pipelines at STScI. DECam photometry will be then combined to the publicly available HST catalog for NGC2808. The merged multi-band deep photometric catalog covering the entire extent of NGC2808 will be used to study the radial distribution of the different multiple stellar populations in the cluster, following the same process adopted in Calamida et al. (2017, AJ, 153, 175).
Numerical simulations will be produced by collaborators Dr. Alessandra Mastrobuono-Battisti (MPIA - Heidelberg) and Dr. Alice Zocchi (ESA-ESTEC) and compared to the observations. The interpretation of the data and models will be done by all the members of the team, and the student will be in charge of writing the paper illustrating the results with the help of the PI. The student will be the first author of the publication.
The main scientific goals we plan to accomplish in this project are:
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