The Orbital Period of Nova V2540 Ophiuchi (2002)

We present the results of 26 nights of CCD photometry of the nova V2540 Oph (2002) from 2003 to 2004. We find a period of 0.284781 +/- 0.000006 d (6.8347 +/- 0.0001 h) in the data. Since this period was present in the light curves taken in both years, with no apparent change in its value or amplitude, we interpret it as the orbital period of the nova binary system. The mass-period relation for cataclysmic variables yields a secondary mass of about 0.75 +/- 0.04 Msolar. From maximum magnitude-rate of decline relation, we estimate a maximum absolute visual magnitude of M_V = -6.2 +/- 0.4 mag. This value leads to an uncorrected distance modulus of (m - M) = 14.7 +/- 0.7. By using the interstellar reddening for the location of V2540 Oph, we find a rough estimate for the distance of 5.2 +/- 0.8 kpc. We propose that V2540 Oph is either (1) a high-inclination cataclysmic variable showing a reflection effect of the secondary star, or having a spiral structure in the accretion disc, (2) a high-inclination intermediate polar system, or less likely (3) a polar.