We prove that if $pge 1$ and $0< rle p$ then the sequence $binom{mp+r}{m}frac{r}{mp+r}$, $m=0,1,2,...$, is positive definite, more precisely, is the moment sequence of a probability measure $mu(p,r)$ with compact support contained in $[0,+infty)$. This family of measures encompasses the multiplicative free powers of the Marchenko-Pastur distribution as well as the Wigners semicircle distribution centered at $x=2$. We show that if $p>1$ is a rational number, $0<rle p$, then $mu(p,r)$ is absolutely continuous and its density $W_{p,r}(x)$ can be expressed in terms of the Meijer and the generalized hypergeometric functions. In some cases, including the multiplicative free square and the multiplicative free square root of the Marchenko-Pastur measure, $W_{p,r}(x)$ turns out to be an elementary function.
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