Physical Properties of 29 sdB+dM Eclipsing Binaries in Zwicky Transient Facility

Abstract

The development of large-scale time-domain surveys provides an opportunity to study the physical properties as well as the evolutionary scenario of B-type subdwarfs (sdB) and M-type dwarfs (dM). Here, we obtained 33 sdB+dM eclipsing binaries based on the Zwicky Transient Facility (ZTF) light curves and Gaia early data release 3 (EDR3) parallaxes.By using the PHOEBE code for light curve analysis, we obtain probability distributions for parameters of 29 sdB+dM. R 1 , R 2 , and i are well determined, and the average uncertainty of mass ratio q is 0.08. Our parameters are in good agreement with previous works if a typical mass of sdB is assumed. Based on parameters of 29 sdB+dM, we find that both the mass ratio q and the companion's radius R 2 decrease with the shortening of the orbital period. For the three sdB+dMs with orbital periods less than 0.075 days, their companions are all brown dwarfs. The masses and radii of the companions satisfy the mass-radius relation for low-mass stars and brown dwarfs. Companions with radii between 0.12R and 0.15R seem to be missing in the observations. As more short-period sdB+dM eclipsing binaries are discovered and classified in the future with ZTF and Gaia, we will have more information to constrain the evolutionary ending of sdB+dM.