A Dance with Dragons: TESS reveals $α$ Draconis is a detached eclipsing binary

Abstract: Detached eclipsing binaries allow stellar masses and radii to be measured with unrivalled accuracy. While inspecting light curves obtained with the Transiting Exoplanet Survey Satellite (TESS), we noticed that the A0 III star $\alpha$ Dra shows clear and well-separated primary and secondary eclipses. This star is known to be a single-lined spectroscopic binary, with a period of 51.5 d and an eccentricity of 0.43. The currently available TESS observations cover two 27-d sectors and the light curve shows a primary eclipse (depth 9%) and a secondary eclipse (depth 2%), separated in time by 38.5 days. Additional TESS observations of $\alpha$ Dra will come from TESS Sectors 16, 21 and 22, and we predict that an eclipse will be visible in each of these. With a $V$ magnitude of 3.68, $\alpha$ Dra is one of the brightest known detached eclipsing binaries.