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S. Sohn (Center for Space Astrophysics, Yonsei U. & Dept. of Astronomy, U. Virginia), S.-C. Rey, Y.-W. Lee (Center for Space Astrophysics, Yonsei U.), B. Chaboyer (Dept. of Physics and Astronomy, Dartmouth College)
The Oosterhoff type II globular cluster M53 is an ideal object for studying the Sandage period-shift effect of RR Lyrae variables among clusters of different Oosterhoff types, since (1) it has a sufficient number of RR Lyrae variables (59 known), (2) the foreground reddening is very small [E(B-V) = 0.02], and (3) it has a HB morphology index similar to M15 but without the blue tail phenomenon which may affect the properties of the RR Lyrae variables.
We present BV CCD photometry for 44 RR Lyrae variables in the metal-poor ([Fe/H] = -1.99) outer halo globular cluster M53 using the data sets obtained with the University of Hawaii 2.2-meter Telescope and the MDM 2.4-meter Hiltner Telescope. The periods and ephemerides are determined and light curves are presented. The mean periods of the RR ab and RRc type variables are < Pab > = 0.67 ± 0.01 day and < Pc > = 0.36 ± 0.01 day, respectively. The mean magnitude of the RR Lyrae variables is < VRR > = 16.82 ± 0.01. We present the color magnitude diagram of M53 including the RR Lyrae variables. The period-amplitude diagram for the RR Lyrae variables in M53 is compared with that of the representative Oosterhoff type I globular cluster M3.
The author(s) of this abstract have provided an email address for comments about the abstract: ss5fb@virginia.edu