Dynamical mass determination and partial eclipses of the heartbeat star HD 181793

We identify the bright Am-type star HD 181793 to be a previously-unknown eclipsing, chemically peculiar heartbeat binary, the second of its kind known. The system carries an orbital period of $P=11.47578275\pm 0.00000055$ days. We use TESS photometry and LCOGT NRES radial velocity data to build a self-consistent orbital model and determine the fundamental stellar characteristics of the primary. We use a spectral separation method to unveil the secondary and measure the masses of both stars. The radial velocity amplitude of the primary, $K_1=47.41+0.13-0.12km{s}^{-1}$, gives a mass $M_1=1.57\pm 0.01$ Msun. The secondary radial velocity amplitude $K_2=84.95+0.12-0.09km{s}^{-1}$ yields a mass ratio $q=0.558\pm 0.002$ and a secondary mass $M_2=0.87\pm 0.01$ Msun. From the spectral energy distribution and Gaia parallax we find a radius $R_1=2.04\pm 0.05$ Rsun. The grazing transit profile and spectroscopic luminosity ratio indicate $R_2=1.04+0.15-0.10$ Rsun, suggesting an early-K spectral type. We show that the heartbeat feature in the TESS light curve can be explained by time-varying ellipsoidal variation, driven by the orbital eccentricity of $e=0.3056+0.0024-0.0026$, and relativistic beaming of the light of the primary. We find no evidence of tidally-excited oscillations.