Modelling the Galactic bar using OGLE-II red clump giant stars

Red clump giant (RCG) stars can be used as distance indicators to trace the mass distribution of the Galactic bar. We use RCG stars from 44 bulge fields from the OGLE-II microlensing collaboration data base to constrain analytic triaxial models for the Galactic bar. We find the bar major-axis is oriented at an angle of 24°–27° to the Sun–Galactic Centre line-of-sight. The ratio of semimajor and semiminor bar axis scalelengths in the Galactic plane x0, y0, and vertical bar scalelength z0, is x0 : y0 : z0= 10 : 3.5 : 2.6, suggesting a slightly more prolate bar structure than the working model of Gerhard which gives the scalelength ratios as x0 : y0 : z0= 10 : 4 : 3.