This paper describes test particle simulations of the response of the outer parts of Galactic disks to barring and spiral structure .
Simulations are conducted for cold Mestel disks and warm quasi-exponential disks with completely flat rotation curves , subjected to pure quadrupoles and logarithmic spirals .
Even though the starting velocity distributions are smooth , the end-points of the bar simulations show bimodality and multi-peaked structures at locations near the outer Lindblad resonance ( OLR ) , although spirality can make this smoother .
The growth of a bar may cause the disk isophotes to become boxy at the OLR , as stars accummulate particularly along the minor axis .
The growth of a bar is also accompanied by substantial heating of the disk stars near the OLR .
For the growth of a 10 ^ { 10 } M _ { \odot } bar , the radial velocity dispersion is typically quadrupled for initially cold disks ( initial \sigma _ { u } \sim 10 km s ^ { -1 } ) , and typically doubled for disks with final \sigma _ { u } \sim 45 km s ^ { -1 } .
Simulations performed of the growth and dissolution of bars give very similar results , demonstrating that the heat once given to disk stars is very difficult to remove .