Eclipsing binaries observed with the WIRE satellite -: I.: Discovery and photometric analysis of the new bright A0 IV eclipsing binary ψ Centauri

Context. Determinations of stellar mass and radius with realistic uncertainties at the level of 1% provide important constraints on models of stellar structure and evolution. Aims. We present a high-precision light curve of the A0IV star psi Centauri, from the star tracker on board the wire satellite and the Solar Mass Ejection Imager camera on the Coriolis spacecraft. The data show that psi Cen is an eccentric eclipsing binary system with a relatively long orbital period. Methods. The wire light curve extends over 28.7 nights and contains 41 334 observations with 2 mmag point-to-point scatter. The eclipse depths are 0.28 and 0.16 mag, and show that the two eclipsing components of psi Cen have very different radii. As a consequence, the secondary eclipse is total. We find the eccentricity to be e = 0.55 with an orbital period of 38.8 days from combining the wire light curve with data taken over two years from the Solar Mass Ejection Imager camera. Results. We have fitted the light curve with EBOP and have assessed the uncertainties of the resulting parameters using Monte Carlo simulations. The fractional radii of the stars and the inclination of the orbit have random errors of only 0.1% and 0.01 degrees, respectively, but the systematic uncertainty in these quantities may be somewhat larger. We have used photometric calibrations to estimate the effective temperatures of the components of psi Cen to be 10450 +/- 300 and 8800 +/- 300 K indicating masses of about 3.1 and 2.0 M-circle dot. There is evidence in the wire light curve for g-mode pulsations in the primary star.