Photometry of eclipsing M+M binary NGTS-EB-8

The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary.

By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2days and the masses and radii of both stars to be M_A_=0.250_-0.004_^+0.005^M_{sun}_, M_B_=0.208_-0.004_^+0.005^M_{sun}_, and R_A_=0.255_-0.005_^+0.004^R_{sun}_, R_B_=0.233_-0.005_^+0.006^R_{sun}_, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (<=0.35M_{sun}_); therefore, they can be a valuable test for stellar evolutionary models.