Openness of the frame set on the hyperbolas

Abstract: We prove that for the functions of the form $g(x) = h(x) + \frac{C}{x+i}$, where $h$ belongs to the continuous Wiener algebra $W_0$, the intersection of the frame set $\mathcal{F}_g$ with every hyperbola ${\alpha, \beta > 0 \mid \alpha\beta = c}$ is open in the relative topology. In particular, this applies to all rational functions $g$.