文摘
We consider polynomials \(P_n\) orthogonal with respect to the weight \(J_{\nu }\) on \([0,\infty )\), where \(J_{\nu }\) is the Bessel function of order \(\nu \). Asheim and Huybrechs considered these polynomials in connection with complex Gaussian quadrature for oscillatory integrals. They observed that the zeros of \(P_n\) are complex and accumulate as \(n \rightarrow \infty \) near the vertical line \({{\mathrm{{\text {Re}}\,}}}z = \frac{\nu \pi }{2}\). We prove this fact for the case \(0 \le \nu \le 1/2\) from strong asymptotic formulas that we derive for the polynomials \(P_n\) in the complex plane. Our main tool is the Riemann–Hilbert problem for orthogonal polynomials, suitably modified to cover the present situation, and the Deift–Zhou steepest descent method. A major part of the work is devoted to the construction of a local parametrix at the origin, for which we give an existence proof that only works for \(\nu \le 1/2\). Keywords Orthogonal polynomials Riemann–Hilbert problems Asymptotic representations in the complex domain Limiting zero distribution Bessel functions