  The intercombination $a^3\Pi - X^1\Sigma^+$ Cameron system of carbon monoxide
has been computationally studied in the framework of multi-reference Fock space
coupled cluster method with the use of generalized relativistic pseudopotential
model for the effective introducing the relativity in all-electron correlation
treatment. The extremely weak $a^3\Pi_{\Omega=0^+,1} - X^1\Sigma^+$ transition
probabilities and radiative lifetimes of the metastable $a^3\Pi$ state were
calculated and compared with their previous theoretical and experimental
counterparts. The impact of a presumable variation of the fine structure
constant $\alpha=e^2/\hbar c$ on transition strength of the Cameron system has
been numerically evaluated as well.
