2004BaltA..13..128S

We present optical spectroscopy and multicolor photometry of the old nova V840 Oph. As part of a long-term project to investigate novae with large outburst amplitudes, we identified this nova via its color characteristics and confirmed it spectroscopically. We find V840 Oph to be one of very few cataclysmic variables showing C IV emission at 580/1 nm. The study of the carbon lines suggests strongly that V840 Oph contains a carbon-rich secondary star. So far, only the nova-like QU Car has been known to have such a companion. We also find spectroscopic evidence that V840 Oph has a hot, dense accretion disc or stream and is probably a magnetic system.