New constraints on a triaxial model of the Galaxy

We determine the most likely values of the free parameters of an N-body mod el for the Galaxy developed by Fur via a discrete-discrete comparison with the positions on the sky and line-of-sight velocities of an unbiased, homog eneous sample of OH/IR stars. Via Monte Carlo simulation, we find the plaus ibility of the best-fitting models, as well as the errors on the determined values. The parameters that are constrained best by these projected data a re the total mass of the model and the viewing angle of the central bar, al though the distribution of the latter has multiple maxima. The other two fr ee parameters, the size of the bar and the (azimuthal) velocity of the Sun, are less well-constrained. The best model has a viewing angle of similar t o 44 degrees, a semimajor axis of 2.5 kpe (corotation radius 4.5 kpc, patte rn speed 46 km s(-1) kpc(-1)), a bar mass of 1.7 x 10(10) M-. and a tangent ial velocity of the local standard of rest of 171 km s(-1). We argue that t he lower values that are commonly found from stellar data fur the viewing a ngle (similar to 25 degrees) arise when too few coordinates Ire available, when the longitude range is too narrow or when low latitudes are excluded f rom the fit, The new constraints on the viewing angle of the Galactic bar f rom stellar line-of-sight velocities decrease further the ability of the di stribution of the bar to account for the observed microlensing optical dept h toward Bande's window: our model reproduces only half the observed value, The signal of triaxiality diminishes quickly with increasing latitude, fad ing within approximately 1 scaleheight (less than or similar to 3 degrees). This suggests that Bande's window is not a very appropriate region in whic h to sample bar properties.