7 Conclusion

We have reported the discovery of a new bright ($V\sim12.6$) cataclysmic variable star identified with the ROSAT X-ray source RX J1643.7+3402. Spectroscopic and photometric observations show it to be a novalike cataclysmic variable sharing several of the characteristics of the SW Sex sub-class of novalike CVs. The spectroscopic period may be either 2 $.\!\!^{\rm h}$575 or 2 $.\!\!^{\rm h}$885, both within the period "gap". A photometric modulation (of $\sim$0.1 mag amplitude in V) with a probable period of 2 $.\!\!^{\rm h}$595 is present on most nights and could be either a "positive" or a "negative" superhump modulation (depending on the exact spectroscopic period), indicating the presence of a precessing accretion disk in this system. Rapid variations of 0.1 to 0.2 mag amplitude in V repeat with a time scale of 15 min. More observations are needed to resolve the spectroscopic period ambiguity, to study the optical modulation and refine its period and to fully characterize the rapid variations.

Acknowledgements

This work was supported by the JUMELAGE "Astrophysique France-Arménie", a bilateral program funded by the French Centre National de la Recherche Scientifique and the French Ministère des Affaires Étrangères. We wish to thank Robert Rutledge and Pablo Rodríguez-Gil for their comments on the manuscript. The Guide Star Catalog and the Digitized Sky Survey were produced at the Space Telescope Science Institute under US Government grants.