A study on the Sagittarius-Carina arm and the halo mass of our galaxy

On the basis of the new Galactic rotation curve and constants R0 and V0, and using HII regions, giant molecular clouds and other tracer objects, we have revised the pattern of the Sagittarius-Carina arm of our Galaxy. We have derived its pitch angle to be about 12°, and explored the dependence of the pitch angle on the Galactic constants. The result indicates that with decreasing Galactic constants, the pitch angle increases, and so does the number of spiral arms, according to the symmetric logarithmic arms model. In addition, the halo mass of our Galaxy will decrease with the flattening and downward turn of the rotation curve.