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 ± 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, K₁ = 47.41+0.13-0.12 km s⁻¹, gives a mass M₁ = 1.57 ± 0.01 Msun. The secondary radial velocity amplitude K₂ = 84.95+0.12-0.09 km s⁻¹ yields a mass ratio q = 0.558 ± 0.002 and a secondary mass M₂ = 0.87 ± 0.01 Msun. From the spectral energy distribution and Gaia parallax we find a radius R₁ = 2.04 ± 0.05 Rsun. The grazing transit profile and spectroscopic luminosity ratio indicate R₂ = 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.