Period Changes of 14,127 Contact Eclipsing Binaries in the Galactic Bulge

We present the orbital-period variations of 14,127 contact eclipsing binaries (CEBs) based on the OGLE-III&IV observations in the Galactic bulge. New times of minimum lights for the CEBs were derived by binary modeling for the full seasonal light curves, which were made from survey observations at an interval of 1 yr. The orbital-period changes of the systems were classified based on the statistical inference, multiple-hypothesis testing error measure, and visual inspection of the eclipse-timing diagrams. As the results, we identified 13,716 CEBs with a parabola, 307 CEBs with a sinusoid, and 104 CEBs with the two variations. The period distributions of the inner close binaries and the outer companions were in the ranges of 0.235-0.990 days and 5.0-14.0 yr, respectively. In our sample of 13,820 CEBs showing a parabolic variation, the highest decreasing and increasing period rates were determined to be <(P)over dot> = -1.38 +/- 0.06 x 10(-5) <(P)over dot>=+8.99 +/- 0.44 x 10(-6) day yr(-1) for OGLE-BLG-ECL-189805, respectively. The secular period change rates were distributed almost symmetrically around zero, and most of them lie within <(P)over dot> = +/- 5.0 x 10(-6) day yr(-1).