For any curve V in a toric surface X, we study the critical locus S ⊂ V of the moment map μ from V to its compactified amoeba μ(V). For any complete linear system |L| given by an ample line bundle L on X, we show that the critical locus S ⊂ V is smooth as long as the curve V is outside of a subset of real codimension 1 in |L|. In particular, the complement of the latter subset appears to be disconnected for general L. It suggests a classification problem analogous to Hilbert's Sixteenth Problem, namely the topological classification of pairs (V, S) for curves V ∈ |L|. The description of the critical locus S in terms of the logarithmic Gauß map γ : V → CP 1 relates the latter problem to the study of the Lyashko-Looijenga map ( ). The map associates to a generic curve V ∈ |L| the unordered set of the critical values of γ on CP 1 . We prove two statements concerning that are crucial for our classification problem: the map is algebraic; the map extends to nodal curves in |L|. This fact allows us to construct many examples of pairs (V, S) by perturbing nodal curves.
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