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We present the first reliable determination of the orbital period of therecurrent nova V2487 Oph (Nova Oph 1998). We derived a value of $0.753 \pm0.016$ d ($18.1 \pm 0.4$ h) from the radial velocity curve of the intense He II$\lambda$4686 emission line as detected in time-series X-shooter spectra. Theorbital period is significantly shorter than earlier claims, but it makes V2487Oph one of the longest period cataclysmic variables known. The spectrum ofV2487 Oph is prolific in broad Balmer absorptions that resemble a white dwarfspectrum. However, we show that they come from the accretion disc viewed at lowinclination. Although highly speculative, the analysis of the radial velocitycurves provides a binary mass ratio $q \approx 0.16$ and a donor star mass $M_2\approx 0.21$ M$_\odot$, assuming the reported white dwarf mass $M_1 = 1.35$M$_\odot$. A subgiant M-type star is tentatively suggested as the donor star.We were lucky to inadvertently take some of the spectra when V2487 Oph was in aflare state. During the flare, we detected high-velocity emission in the Balmerand He II $\lambda$4686 lines exceeding $-2000$ km s$^{-1}$ at close to orbitalphase 0.4. Receding emission up to $1200$ km s$^{-1}$ at about phase 0.3 isalso observed. The similarities with the magnetic cataclysmic variables maypoint to magnetic accretion on to the white dwarf during the repeating flares.

The orbital period of the recurrent nova V2487 Oph revealed