Abstract
Abstract VZ Lib is a southern triple-lined system. By analyzing all available times of light minima, orbital period changes are revisited in detail. We discovered that the observed–calculated (O − C) curve shows a long-term period decrease at a rate of , revealing a mass transfer from the more massive component to the less massive one. A cyclic variation covering more than three cycles was discovered, which was analyzed for the light-travel-time effect via the presence of the tertiary companion. The cyclic variation has a short period of 2.96 (±0.04) yr and a small semiamplitude of 0.0039 (±0.0004) days. The mass of the third body was determined to be M ⊙ and an orbital semimajor axis shorter than au was obtained. Orbital properties of this close-in companion should provide valuable information on the formation of close binaries and stellar dynamical interaction. New complete light curves of VZ Lib were obtained and modeled with the Wilson–Devinney code. The light curves show a small but significant O’Connell effect that was not detectable in 1981 and 2007 but in 2004, so we derived a new photometric solution with assuming spot and a third light in the system. It is found that the light-curve subtype changed from A-type to W-type, which was possibly caused by a dark spot on the massive component. Our photometric solutions are in agreement with the spectroscopic results given by previous authors.
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