${\mathrm{\Sigma }}_1$-Stationary logic as an ${\mathrm{\aleph }}_1$-Abstract Elementary Class

$\mu$-Abstract Elementary Classes are a model theoretic framework introduced in [BGL+16] to encompass classes axiomatized by ${\mathbb{L}}_{\mathrm{\infty },\mathrm{\infty }}$. We show that the framework extends beyond these logics by showing classes axiomatized in $\mathbb{L}(aa)$ with just the $aa$ quantifier are an ${\mathrm{\aleph }}_1$-Abstract Elementary Class.