Four-colour photometry of eclipsing binaries. XIII. A photometric elements and absolute dimensions of TY Pyx.

Previously published (Andersen et al., 1981) uvby light curves of the double-lined eclipsing binary TY Pyxidis, are analyzed to obtain the photometric elements and absolute dimensions of the system. Observed b light curve and b-y and u-b color curves are derived and determinations of the time of primary minimum are used to obtain an improved ephemeris. The uvby light curves are noted to exhibit the distortion typical of RS CVn binaries, however to a much smaller extent (range 0.03 mag) than in other RS CVn stars. Photometric elements for the system are derived by means of the binary model of Wood (1971) and a light curve simulation program, and combined with spectroscopic results to determine accurate absolute dimensions for the system, including primary and secondary masses of 1.22 and 1.20 solar masses, radii of 1.59 and 1.68 solar radii and log surface gravities of 4.12 and 4.07, respectively. Data are found to be consistent with a model of age 10-20 billion years, and composition of (X,Z) = (0.80, 0.04).