Rediscussion of eclipsing binaries. Paper XXVI. The F-type long-period system HP Draconis

Abstract

HP Dra is a well-detached eclipsing binary containing two late-F stars on an orbit with a relatively large period of 10.76 d and a small eccentricity of 0.036. It has been observed in 14 sectors using the Transiting Exoplanet Survey Satellite (TESS). We use these data plus literature spectroscopic measurements to establish the properties of the component stars to high precision, finding masses of 1.135 +/- 0.002 Msun and 1.098 +/- 0.002 Msun and radii of 1.247 +/- 0.005 Rsun and 1.150 +/- 0.005 Rsun. We find a much smaller third light than previous analyses, resulting in significant changes to the measured radii. These properties match theoretical predictions for an age of 3.5 Gyr and a solar metallicity. We present a spectrum of the Ca H and K lines in which chromospheric activity is visible from both components. The distance we find to the system, 77.9 +/- 1.2 pc, matches the Gaia DR3 parallax value of 79.2 +/- 0.3 pc.