  Determinations of stellar mass and radius with realistic uncertainties at the
level of 1% provide important constraints on models of stellar structure and
evolution. 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.
The WIRE light curve extends over 28.7 nights and contains 41334 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. 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 Msun. There is evidence in the WIRE light curve for g-mode
pulsations in the primary star.
