Karman's family of point vortex streets is unstable for all aspect ratios, being linearly stable for only a single value of aspect ratio. This property has been reported to hold for some more complicated families of vortex streets. It is proved here that all one-parameter families of two-dimensional inviscid x-periodic equilibrium vortex systems 'close enough' to the point vortex street family have at most one linearly stable parameter value. In fact, for perturbed systems preserving the back-to-fore symmetry, the form of the stability diagram, essentially persists, while if the back-to-fore symmetry is broken all aspect ratios typically become linearly unstable. The proof is based on the Hamiltonian nature of the Euler equations, calculation of the codimension and unfolding for a particular conjugacy class in the space of linear Hamiltonian systems, and transversality of the family of linear systems arising from the point vortex streets to this conjugacy class. It is not clear, however, whether our closeness condition is implied by the natural closeness condition on vorticity distributions.
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