CCD Photometry of Galactic Globular Clusters.III.IC 4499

Abstract

The variable star population of the Oosterhoff Type I galactic globular cluster IC 4499 (C1452-820) has been studied by CCD photometry, from observations in the B, V, R, and I passbands made during the period 1987-1994. Light curves have been prepared for 97 RR Lyrae variables and one variable blue-straggler (SX Phe) star. The RR Lyraes have &lt;V&gt;=17.65±0.01, and via several methods E(B-V)=0.22±0.02, with [Fe/H]=-1.65. The cluster contains a substantial number (17) of double-mode (RRd) variables, and period ratios are determined for 16 of these; it is near-constant, P<SUB>1</SUB>/P<SUB>0</SUB>=0/74432±0.00003 (s.e.). Calibrating using pulsation models by Cox, the mean mass is found to be 0.70±0.02 M<SUB>sun</SUB> and the Oosterhoff lI-Osterhoff I mass difference, comparing with similar observations of the M68 RRd stars, is 0.05±0.02 M<SUB>sun</SUB>. Four stars are identified as second-overtone (RRe) pulsators. The distribution of stars on the horizontal branch (HB) is compared with predictions from evolution and pulsation theory.