  The electronic, laser-induced fluorescence spectrum of the
$B^2\Sigma^+\leftarrow X^2\Sigma^+$ transition in $^{28}$Si$^{16}$O$^+$ and
$^{29}$Si$^{16}$O$^+$ has been recorded in a cryogenic buffer gas cell at
$\approx$ 100 K. Molecular constants are extracted for both
$^{28}$Si$^{16}$O$^+$ and $^{29}$Si$^{16}$O$^+$, including the Fermi contact
hyperfine constant for both the $B$ and $X$ states of $^{29}$Si$^{16}$O$^+$,
and used in a discussion of the suitability of SiO$^+$ in future quantum
information experiments.
