V455 Aur is a detached eclipsing binary containing two F-stars in a 3.15-d orbit with a small eccentricity. Its eclipses were discovered in data from the Hipparcos satellite and a spectroscopic orbit was obtained by Griffin (2001, 2013). Griffin found a long-term variation of the systemic velocity of the eclipsing system due to a third body in a highly eccentric orbit (e = 0.73) with a period of 4200 d. We have used these data, the light curve of V455 Aur from the TESS satellite, and the Gaia EDR3 parallax to determine the physical properties of the components of the system to high precision. We find the eclipsing stars to have masses of 1.289 +/- 0.006 Msun and 1.232 +/- 0.005 Msun, radii of 1.389 +/- 0.011 Rsun and 1.318 +/- 0.014 Rsun and effective temperatures of 6500 +/- 200 and 6400 +/- 200 K. Light from the tertiary component is directly detected for the first time, in the form of a third light of l_3 = 0.028 +/- 0.002 in the solution of the TESS light curve. From this l_3, theoretical spectra and empirical calibrations we estimate the star to have a mass of 0.72 +/- 0.05 Msun, a radius of 0.74 +/- 0.05 Rsun and a temperature of 4300 +/- 300 K. The inclination of the outer orbit is 53 +/- 3 degrees, so the two orbits in the system are not coplanar. We show that a measured spectroscopic light ratio of the two eclipsing stars could lower the uncertainties in radius from 1% to 0.25%. A detailed spectroscopic analysis could also yield precise temperatures and chemical abundances of the system, thus making V455 Aur one of the most precisely measured eclipsing systems known.
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