MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.407, no.1, pp.497-506, 2010 (Journal Indexed in SCI)
We present results from analysing new spectroscopic and photometric observations of the KZ Pav (IDS 20490-7048 A-BC) multiple system. High-resolution spectra were taken at the Mt John University Observatory in 2007 and 2008. Radial velocities for the close binary were determined from cross-correlation and spectral disentangling methods. The resulting orbital elements are a(1) sin i = 0.0103 +/- 0.0001 au, a(2) sin i = 0.0158 +/- 0.0001 au, M(1) sin3i = 1.598 +/- 0.006 M(circle dot) and M(2) sin3i = 1.045 +/- 0.006 M(circle dot). The close binary components rotated synchronously according to their Mg i (5183.6 A) line profiles. Four photometric data sets (1988-89 BV, 1998 V, Hipparcos and 2006 BVRI) were modelled with modern light-curve synthesis methods. The radial velocity models, including proximity effects, give the close binary mass ratio as 0.641 +/- 0.003. The combination of the photometric light and radial velocity data gives the following absolute parameters: M(1) = 1.70 +/- 0.02 M(circle dot), M(2) = 1.09 +/- 0.03 M(circle dot), R(1) = 1.74 +/- 0.01 R(circle dot), R(2) = 1.94 +/- 0.02 R(circle dot), L(1) = 5.86 +/- 0.81 L(circle dot) and L(2) = 2.32 +/- 0.40 L(circle dot). The distance to KZ Pav is 115 +/- 8 pc from our analysis, taking into account interstellar extinction. The orbital period of the close binary, from times of minimum data covering nearly one century, indicates a quasi-sinusoidal form superimposed on a downward parabola. The secular period decrease was interpreted in terms of the combined effects of mass transfer and loss. The sinusoidal component may reflect a light-time effect from either an unseen component or higher order terms in perturbations from the BC system, or perhaps an internal magnetic field rearrangement (Applegate type) mechanism. The orbits of the A-BC and B-C systems are considered against historic astrometric measurements.