Vol 22, No 3

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

#### Min Dai, Xiao-Dian Chen, Kun Wang, Yang-Ping Luo, Shu Wang, Li-Cai Deng

Abstract

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 (sdBs) and M-type dwarfs (dMs). 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+dMs. R1, R2 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+dMs, we find that both the mass ratio q and the companion’s radius R2 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 0.12 $$R_{\odot}$$ and 0.15 $$R_{\odot}$$ 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+dMs.

Keywords

Keywords (stars:) binaries: eclipsing – stars: evolution – (stars:) subdwarfs – (stars:) brown dwarfs

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