Notes on the starlike log--harmonic mappings of order alpha

Abstract

Let $h$ and $g$ be two analytic functions in the unit disc $\Delta$ that $g(0)=1$. Also let $\beta$ be a complex number with ${\rm Re}\{\beta\}>-1/2$. A function $f$ is said to be log--harmonic mapping if it has the following representation \begin{equation*} f(z)=z |z|^{2\beta} h(z)\overline{g(z)}\quad (z\in \Delta). \end{equation*} A log--harmonic mapping $f$ is said to be starlike log--harmonic mapping of order $\alpha$, where $0\leq \alpha<1$, if \begin{equation*} {\rm Re}\left\{\frac{zf_z -\overline{z}f_{\overline{z}}}{f}\right\}>\alpha\quad(z\in \Delta). \end{equation*} In this paper, by use of the subordination principle, we study some geometric properties of the starlike log--harmonic mappings of order $\alpha$. Also, we estimate the Jacobian of log--harmonic mappings.