NOAO >   Observing Info >   Approved Programs >   2013B-0367

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Proposal Information for 2013B-0367


PI: Andrea Kunder, Cerro Tololo Inter-American Observatory, akunder@ctio.noao.edu
Address: Astronomy Department, Casilla 603, La Serena, IV, Chile

CoI: Peter B. Stetson, Canadian Astronomy Data Centre
CoI: Marcio Catelan, Pontificia Universidad Catolica de Chile
CoI: Christian I. Johnson, UCLA
CoI: Mario Soto, STScI
CoI: Santi Cassisi, INAF-Osservatorio Astronomico di Collurania
CoI: Alistair Walker, Cerro Tololo Inter-American Observatory

Title: The RR Lyrae Instability Strip in the Split Horizontal Branch Globular Cluster NGC 6569

Abstract: We propose to obtain UBVI photometry of the 28 RR Lyrae variables in the Galactic globular cluster NGC 6569, a cluster which has recently been shown to harbor two horizontal branches. NGC 6569 is one of only three globular clusters in the Galaxy known to have a double horizontal branch, but unlike the other clusters with a double horizontal branches, we have identified 28 RR Lyrae variables residing in its core from archival data. The observations proposed here will allow us to make, for the first time, an ultraviolet (UV) color magnitude diagram of the instability strip and an accurate period- amplitude diagram of the RR Lyrae stars in this cluster. Whether the RR Lyrae stars show two populations or whether they originated from only one of the horizontal branches allows an understanding on the mechanism driving the multiple population phenomenon in this highly unusual cluster. Comparing the RR Lyrae properties (e.g., periods, amplitudes, oosterhoff classification) of NGC 6569 to ``normal" Milky Way globular clusters as well as to the Milky Way's satellite dwarf galaxies, a tracing of the merging episodes that led to the assembly of the Galaxy will be obtained. Lastly, the colors and amplitudes of the RR Lyrae stars in NGC 6569 will allow investigations on the differential reddening across the horizontal branch.


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