We report a measurement of the streaming motion of the stars in the Galactic bar with the Red Clump Giants ( RCGs ) using the data of the Optical Gravitational Lensing Experiment II ( OGLE-II ) .
We measure the proper motion of 46,961 stars and divide RCGs into bright and faint sub-samples which on average will be closer to the near and far side of the bar , respectively .
We find that the far-side RCGs ( 4,979 stars ) have a proper motion of \Delta < \mu > \sim 1.5 \pm 0.11 mas yr ^ { -1 } toward the negative l relative to the near-side RCGs ( 3,610 stars ) .
This result can be explained by stars in the bar rotating around the Galactic center in the same direction as the Sun with v _ { b } \sim 100 km s ^ { -1 } .
In the Disc Star ( DS ) and Red Giant ( RG ) samples , we do not find significant difference between bright and faint sub-samples .
For those samples \Delta < \mu > \sim 0.3 \pm 0.14 mas yr ^ { -1 } and \sim 0.03 \pm 0.14 mas yr ^ { -1 } , respectively .
It is likely that the average proper motion of RG stars is the same as that of the Galactic center .
The proper motion of DSs with respect to RGs is \sim 3.3 mas yr ^ { -1 } toward positive l .
This value is consistent with the expectations for a flat rotation curve and Solar motion with respect to local standard of rest .
RGs have proper motion approzimately equal to the average of bright and faint RCGs , which implies that they are on average near the center of the bar .
This pilot project demonstrates that OGLE-II data may be used to study streaming motions of stars in the Galactic bar .
We intend to extend this work to all 49 OGLE-II fields in the Galactic bulge region .