On the automorphism group of a toral variety

Let $\mathbb{K}$ be an algebraically closed field of characteristic zero. An affine algebraic variety $X$ over $\mathbb{K}$ is toral if it is isomorphic to a closed subvariety of a torus $({\mathbb{K}}^{\ast }{)}^d$. We study the group $\mathrm{A}\mathrm{u}\mathrm{t}(X)$ of regular automorpshims of a toral variety $X$. We prove that if $T$ is a maximal torus in $\mathrm{A}\mathrm{u}\mathrm{t}(X)$, then $X$ is a direct product $Y\times T$, where $Y$ is a toral variety with a trivial maximal torus in the automorphism group. We show that knowing $\mathrm{A}\mathrm{u}\mathrm{t}(Y)$, one can compute $\mathrm{A}\mathrm{u}\mathrm{t}(X)$. In the case when the rank of the group $\mathbb{K}[Y{]}^{\ast }\mathrm{/}{\mathbb{K}}^{\ast }$ is $\dim Y+1$, the group $\mathrm{A}\mathrm{u}\mathrm{t}(Y)$ can be described explicitly.