SIMBAD references

We apply the method of smoothed particle hydrodynamics (SPH) in gaseous disks, in order to analyze the response of the gas to an imposed spiral potential. The study is confined to open spiral patterns. Our simulations of strong spirals with relatively high pattern speeds of the density wave, which place the Outer Lindblad Resonance (OLR) or corotation at the end of the spiral arms observed in red light, do not allow us to accept a model with these properties. The OLR models typically present a weak spiral pattern up to corotation, which is in general not well aligned with the potential minima, and a stronger response, tighter than the imposed spiral pattern, in the outer parts. In very non-linear disks a ring is formed between the -4/1 resonance and the OLR. An oval ring, especially in viscous disks, is formed in the OLR area. In one case we found good response of the density maxima of the 2θ component up to corotation. In the corotation case, logarithmic spirals can be traced only close to the center. We find box-like structures at the 4/1 radius, and segments of arms in the outer parts of the disk. If we place the end of the observed spirals at the 4/1 resonance, the resulting spiral arms extend without serious difficulties from the center or the Inner Lindblad Resonance (ILR) to the assumed end of the spirals, remaining close to the imposed potential minima. By increasing the non-linearity and/or the viscosity of the models, we observe several changes in the response of the gas. However these changes do not affect their general behaviour.