TOI-1830 and TOI-1312: Two EBs hosting very low-mass stellar companions in eccentric orbits

We describe in the underlying investigation the discovery of two eclipsing binary systems. In both cases, the companions are most likely fully convective low-mass stars. The TESS team initially alerted the systems as TOI-1830 (TIC20182165, HD133725) and TOI-1312 (TIC405904232), and we subsequently observed them with spectroscopy. The TESS light curves and spectroscopic observations were analyzed in a combined data-driven framework to estimate the systems’ parameters. Radial velocity (RV) measurements with LCO/NRES, NOT/FIES, SONG, and TRES indicated for the TOI-1830 system a companion mass of 0.11 M☉ in a 9.781-day eccentric orbit and a 0.10 M☉ companion in an 11.080-day eccentric orbit for the TOI-1312 system. At the same time, the spectroscopic observations were used to estimate the spectral type of the main stars for TOI-1830 and TOI-1312. We measured the radii ratio from the TESS light curves and estimated the companions’ radii, assuming the main stars’ radii as measured from spectroscopy and isochrones. Given the youth of TOI-1830 and the evolved age of TOI-1312, both systems will provide valuable insights into the stellar evolution of close binary systems.