Orbital and quasi-periodic optical variations in the black hole X-ray binary V404 CYG

Pavlenko, E. P.; Martin, A. C.; Casares, J.; Charles, P. A.; Ketsaris, N. A.
Referencia bibliográfica

Monthly Notices of the Royal Astronomical Society, Volume 281, Issue 3, pp. 1094-1104.

Fecha de publicación:
8
1996
Número de autores
5
Número de autores del IAC
0
Número de citas
28
Número de citas referidas
24
Descripción
We present 2 weeks of CCD photometry of V404 Cyg, the optical counterpart of the soft X-ray transient (SXT) GS 2023+338, taken from La Palma in 1992 July. The R-band light curve shows a clear 0.3-mag ellipsoidal modulation on the estabished 6.5-d orbital period, but with substantial (up to 0.3 mag) superposed variations that occur during each night on a time-scale of 6 h. We model both the mean orbital light curve and its lower envelope (which we presume to show the secondary star with minimum contamination from the accretion disc). With a mass ratio already known from the optical spectroscopy of Casares & Charles, the analysis of the lower envelope light curve leads to an orbital inclination of i=56 deg+/-2 deg. Our best model requires no hotspot contribution. The shorter time-scale of variability is consistent with the 6-h quasi-periodicities that have been seen in outburst and during the early quiescent period. Using periodogram analysis, we find three components of the 6-h peak (at 5.90, 6.07 and 6.24 h). The periodograms show the outside peaks to be stronger than the smaller, central peak. A peak in the power spectrum at 4.5 d coincides with the beat period of these outside peaks. The nature of these periodicities is unknown.