Among over 200,000 Galactic Bulge variable stars in the public domain OGLE catalogue , we found over 15,000 red giant variables following two well defined period – amplitude relations .
The periods are in the range 10 < P < 100 days , and amplitudes in the range 0.005 < A < 0.13 mag in 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 a rms scatter of only 0.44 mag .
The average magnitudes for these stars are well correlated with the Galactic longitude , and vary from I _ { k, 0 } = 11.82 for l = +8 ^ { \circ } to I _ { k, 0 } = 12.07 for l = -5 ^ { \circ } , clearly indicating that they are located in the Galactic Bar .
Most variables have several oscillation periods .