Long-term optical/infrared variability in the quiescent X-ray transient V404 Cyg

We present the results of optical and infrared photometry of the quiescent X-ray transient V404 Cyg during the period 1992–2003. The ellipsoidal modulations extracted from the most complete databases (years 1992, 1998 and 2001) show unequal maxima and minima with relative strength varying from year to year although their peak to peak amplitudes remain roughly constant at 0.24±0.01 magnitudes. Fast optical variations superimposed on the secondary star’s double-humped ellipsoidal modulation were detected every year with a mean amplitude of ∼0.07mags. We have not found significant changes in the activity during this decade which indicates that this variability is probably not connected to the 1989 outburst. We have found periodicities in the 1998 and 2001 data near the 6 hr quasi-periodicity observed in 1992, although we interpret it as consequence of the appearance of a flare event almost every night. Significant variability is also present in the I and near infrared (J and Ks) bands and this decreases slightly or remains approximately constant at longer wavelengths. A cross correlation analysis shows that both the R and I emission are simultaneous down to 40 s.