CCD Photometry of the Globular Cluster M53. I. Color-Magnitude Data and Blue Straggler Stars

Citations Over TimeTop 13% of 1998 papers

Abstract

The rst large-format CCD color-magnitude diagram (CMD) in the B and V passbands is presented for the Galactic globular cluster M53 (NGC 5024). The observations consist of 40 pairs of B and V CCD frames with in a pattern covering a 12@ ] 13@ region of M53. These frames were FWHM \ 1A .2 used to produce color-magnitude data for more than 20,000 stars from the tip of the red giant branch (RGB) to about 2 mag below the main-sequence turno (V D 22). The CMD reveals a classic example of a metal-poor stellar system, with the horizontal branch (HB) predominantly blueward of the RR Lyrae instability strip and the relatively steep RGB. The blue HB of M53 does not show the blue tail phenomenon that is observed in M15. The relative age dating based on the color di erence between the turno and the base of RGB reveals no signicant age di erence (*t \ 1 Gyr) between M53 and M92. We have discovered 114 new blue straggler stars (BSSs) in the eld of M53. The analysis of bright (V \ 19.39) BSSs clearly shows a bimodal radial distribution with a high frequency in the inner and outer regions but a distinct dip in the intermediate region. The distribution is similar to that found in M3, a globular cluster with a similar central density and concentration.

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