HD 144548: A young triply eclipsing system in the Upper Scorpius OB association

The star HD 144548 (= HIP 78977; TYP 6212-1273-1) has been known as a detached eclipsing binary and a bona-fide member of the Upper Scorpius OB association. Continuous photometry from the K2 mission on Campaign Two has revealed the presence of additional eclipses due to the presence of a third star in the system. These are explained by a system composed of the two previously known members of the eclipsing system (Ba and Bb) with a period of 1.63 d, orbiting around an F7-F8V star with a period of 33.945 +/- 0.002 d in an eccentric orbit (e(A) = 0.2652 +/- 0.0003). The timing of the eclipses of Ba and Bb reveals the same 33.9 d periodicity, which we interpret as the combination of a light time effect combined with dynamical perturbations on the close system. Here we combine radial velocities and analytical approximations for the timing of the eclipses to derive masses and radii for the three components of the system. We obtain a mass of 1.44 +/- 0.04 M-circle dot and radius of 2.41 +/- 0.03 R-circle dot for the A component, and almost identical masses and radii of about 0.96 M-circle dot and 1.33 R-circle dot for each of the two components of the close binary. HD 144548 is the first triply eclipsing system for which radial velocities of all components could be measured.