Binary Fraction Estimation of Main-sequence Stars in 12 Open Clusters: Based on the Homogeneous Data of LAMOST Survey and Gaia DR2

Based on the homogeneous low-resolution spectra data observed by Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and the Gaia Data Release 2 (Gaia DR2) photometric data, we chose 12 open clusters (OCs) to study their fundamental parameters and binary fractions (BFs). For each OC, more than 20 cluster members were observed by LAMOST, and some of them were observed multiple times. We used these data to derive precise metallicities of OCs. Combining the metallicities and the Gaia DR2 photometric data, we used the isochrone fitting method to obtain fundamental parameters of these OCs. By fixing metallicity during the fitting, we avoided the effect of degeneracy between the metallicity and reddening. Based on the fundamental parameters, we utilized the synthetic color-magnitude diagram (CMD) method to derive the BFs of main-sequence (MS) stars, the mass functions (MFs) with correction of binaries, and the companion mass ratio distributions. The BFs of observed MS stars in OCs in this paper vary from 29% to 55%. Extrapolating the synthetic CMD to the hydrogen-burning limit, the BFs vary from 13% to 47%. Combining MFs published by previous literature with our results, we found that MFs with correction of binaries were steeper than those without correction by Δ = 0.6 0.16 in the mass range of m [1M , 2.67M ]. We found that the companion mass ratio distribution in OCs of our sample was flat. We also found a significant positive correlation between the BF and density.