ATLAS results on charmonium production and $B_c$ production and decays

Recent results from the proton-proton collision data taken by the ATLAS experiment on the charmonium production and on the $B_c$ production and decays will be presented. The measurement of the associated production of the $J/\psi$ meson and a gauge boson, including the separation of single and double parton scattering components, will be discussed. The measurement of $J/\psi$ and $\psi(2S)$ differential cross sections will be reported as measured on the whole Run 2 dataset. The measurement of the differential ratios of the $B_c^+$ and $B^+$ production cross sections at 8 TeV will also be shown. New results on the $B_c$ decays to $J/\psi D_s^{(*)}$ final states obtained with the Run 2 data at 13 TeV will be detailed.