NOAO >   Observing Info >   Approved Programs >   2010A-0311

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Proposal Information for 2010A-0311


PI: Ata Sarajedini, University of Florida, ata@astro.ufl.edu
Address: Astronomy Department, 211 Bryant Space Science Center, Gainesville, FL 32611-2055, United States

CoI: Shashi Kanbur, SUNY - Oswego
CoI: Karen Kinemuchi, University of Florida
CoI: Chow Choong Ngeow, National Central University

Title: Unlocking the Secrets of the Oosterhoff Effect: A Period-Amplitude-Color Analysis of RR Lyrae Variables

Abstract: Within our Galaxy, globular clusters can be divided into two distinct groups based on the properties of their RR Lyrae (RRL) variable stars: Oosterhoff I and II (OoI and OoII). Fundamental mode RRL in the two types of clusters exhibit not only different average periods (0.55 and 0.65 days, respectively, for OoI and OoII), but also very different Period-Amplitude (PA) relations. One possible explanation in the literature is that OoII clusters are more evolved than OoI. We propose to construct well sampled multicolor observations of Galactic globular clusters that currently have few time series observations. Adding these observations to the existing data, we will formulate Period-Color (PC) and Amplitude-Color (AC) relations as a function of pulsation phase and Oosterhoff type. The resulting relations will permit a more detailed comparison of RRL properties with Oosterhoff type. It can be demonstrated that PA relations can be decomposed into PC and AC relations at maximum and minimum light, which can be traced to the interaction of the stellar photosphere and hydrogen ionization front, which in turn, may depend on the evolutionary status of the star. Further, our multiphase, multicolor observations will be able to place significantly stronger constraints on the pulsation models of RRL stars than has hitherto been possible.


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