Description
Among over 200000 Galactic bulge variable stars in the public domain Optical Gravitational Lensing Experiment (OGLE) catalogue, we found over 15000 red giant variables following two well-defined period-amplitude relations. The periods are in the range 10<P<100d, and amplitudes in the range 0.005<A<0.13mag in the I band. The variables cover a broad range of reddening-corrected colours, 1<(V-I)_0_<5, and a fairly narrow range of extinction-corrected apparent magnitudes, 10.5<I_0_<13. A subset of variables (type A) has an rms scatter of only 0.44mag. The average magnitudes for these stars are well correlated with the Galactic longitude, and vary from I_k,0_=11.82 for l=+8{deg} to I_k,0_=12.07 for l=-5{deg}, clearly indicating that they are located in the Galactic bar. Most variables have several oscillation periods.
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