OGLE small amplitude red giant variables in the Galactic Bar

Abstract

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 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.