Eclipse time variations in the post-common envelope binary V470 Cam

Abstract

ABSTRACT Linear or quadratic relations fitted to the time-dependence of post-common envelope binary eclipse times generally give residuals exhibiting a cyclic variation. Among several possible explanations is the presence of one or more orbiting circumbinary objects causing a reflex motion of the binary centre-of-mass, thereby altering the light-travel-time.Twenty new eclipse times for the post-common envelope binary V470 Cam have been obtained; with these and 380 useable eclipse times in the literature, two circumbinary brown dwarfs having orbital periods of 7.87 ± 0.08 and 13.27 ± 0.16 yr were found to give an excellent fit to cyclic residuals resulting from a quadratic ephemeris fit. Irrespective of the excellent fit, it would be premature to claim that the V470 Cam binary is accompanied by two orbiting brown dwarfs; at the very least more eclipse times are needed to confirm the result and other plausible explanations, such as the Applegate mechanism, need eliminating.