2024MNRAS.532.4304U

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 $P = 11.47578275 \pm 0.00000055$ d. 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, $K_1 = 47.41\, {^ {+0.13}}_ {-0.12}$ km s^–1, gives a mass $M_1 = 1.57 \pm 0.01$ M$_\odot$. The secondary radial velocity amplitude $K_2 = 84.95\, {^ {+0.12}}_ {-0.09}$ km s^–1 yields a mass ratio $q = 0.558 \pm 0.002$ and a secondary mass $M_2 = 0.87 \pm 0.01$ M$_\odot$. From the spectral energy distribution and Gaia parallax, we find a radius $R_1 = 2.04 \pm 0.05$ R$_\odot$. The grazing transit profile and spectroscopic luminosity ratio indicate $R_2 = 1.04\, {^ {+0.15}}_ {-0.10}$ R$_\odot$, 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.