NOAO >   Observing Info >   Approved Programs >   2012B-0178

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Proposal Information for 2012B-0178


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

CoI: Peter B Stetson, Canadian Astronomy Data Centre
CoI: Giuseppe Bono, University of Rome Tor Vergata
CoI: Santi Cassisi, INAF-Osservatorio Astronomico di Collurania
CoI: Marcio Catelan, Pontificia Universidad Catolica de Chile
CoI: Brian Chaboyer, Dartmouth College
CoI: James Clem, Lousiana State University
CoI: Andy Layden, Bowling Green State University
CoI: Noriyuki Matsunaga, Kiso Observatory, University of Tokyo
CoI: Maurizio Salaris, Liverpool John Moores University
CoI: Alistair Walker, Cerro Tololo Inter-American Observatory

Title: CCD Photometry of the M22 RR Lyrae Instability Strip

Abstract: We propose to determine the mean colors, amplitudes and Oosterhoff properties of the RR Lyrae variables (RRLs) in the peculiar, bimodal- horizontal branch of the Galactic globular cluster NGC 6656 (M22). NGC 6656 is known to host multiple stellar populations and a sizeable population of RR Lyrae variables have been identified (Wehlau & Sawyer 1977, 1978). The similarities between \omega Cen and M22 suggest that like the two (at least) populations of RR Lyrae variables that co-exist in \omega Cen, there may be distinct populations of RR Lyrae variables residing in M22. We will obtain for the first time, accurate CCD photometry of the RR Lyrae stars in M22 to make a calibrated period- amplitude diagram of the RR Lyrae stars in this cluster and investigate any bi-modality in the instability strip. The colors and amplitudes of the RR Lyrae in M22 will allow investigations on the metallicities of the RR Lyrae stars as well as differential reddening across the horizontal branch of this cluster. Lastly, this detailed study of the instability strip of M22 will allow an updated horizontal branch parameter, with which to model the HB. As M22 is one of the few GCs for which reliable estimates of the C+N+O sum exist and this can greatly help in constraining the HB morphology and the RR Lyrae properties.


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