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We derive the distribution of maser stars in the inner Milky Way (MW) basedon an analysis of lV-diagrams (lVd) for two samples of maser stars: 771 OH/IRstars and 363 SiO-maser stars. They are all close to the plane of the MW andhave long. from -45 to +45deg. The two lVds are compared and found to be verysimilar. They also compare well with the lVd of interstellar CO, but there aresignificant differences in detail between the stellar lVds and that of the ISM.Based on the qualitative discussion we divide the lVds into seven areas. Ineach area we compare the number of stars observed with those predicted by anassumed set of orbits in a galactic potential. This potential is axiallysymmetric but a weak rotating bar has been added. We conclude that the maserstars move on almost circular orbits outside of about 3.5 kpc, but that theorbits become more and more elongated when one goes deep inside our MW. We finda strong effect of the Corotation (CR) resonance (res) at 3.3 kpc, we see asmall but noticeable effect of the Outer Lindblad res at 5 kpc and no effect ofthe Inner Lindblad res at r=0.8 kpc. We find a set of 6 groups of orbits thattogether predict counts in agreement with the counts of stars observed. We thencalculate the trajectory of each orbit and so find the distribution of themaser stars in the plane of the MWG. This distribution has two new (but notunexpected) features. The first is a bar-like distribution within 2 kpc fromthe GC outlined. These orbits explain the high-vel stars near l=0deg in theforbidden and the permitted quadrants. The second feature are two"croissant"-like voids in the distribution close to the CR radius (3.3 kpc),which are the consequence of the presence of the CR res. We find excellentagreement with an earlier reconstruction by Sevenster (1999).Comment: 16 pages, 8 figures. Accepted by Astronomy & Astrophysic

The distribution of maser stars in the inner Milky Way: the effect of a weak, rotating bar