2018AJ....156...27C

Eclipsing binaries (EBs) with one of the companions as very low-mass stars (VLMSs; or M dwarfs) are testbeds to substantiate stellar models and evolutionary theories. Here we present four EB candidates with F-type primaries, namely, SAO 106989, HD 24465, EPIC 211682657, and HD 205403, identified from different photometry missions, SuperWASP, Kilodegree Extremely Little Telescope (KELT), Kepler 2 (K2), and Solar Terrestrial Relations Observatory (STEREO). Using the high-resolution spectrograph PRL Advanced Radial velocity Abu-sky Search at the 1.2 m telescope at Mount Abu, Rajasthan, India, we hereby report the detection of four VLMSs as companions to the four EBs. We performed spectroscopic analysis and found the companion masses to be 0.256 ± 0.005, 0.233 ± 0.002, 0.599 ± 0.017, and 0.406 ± 0.005 M_☉ for SAO 106989, HD 24465, EPIC 211682657, and SAO 106989B, respectively. We determined orbital periods of 4.39790 ± 0.00001, 7.19635 ± 0.00002, 3.142023 ± 0.000003, and 2.444949 ± 0.000001 days and eccentricities of 0.248 ± 0.005, 0.208 ± 0.002, 0.0097 ± 0.0008, and 0.002 ± 0.002 for EBs SAO 106989, HD 24465, EPIC 211682657, and HD 205403, respectively. The radii derived by modeling the photometry data are 0.326 ± 0.012 R_☉ for SAO 106989, 0.244 ± 0.001 R_☉ for HD 24465B, 0.566 ± 0.005 R_☉ for EPIC 211682657B, and 0.444 ± 0.014 R_☉ for HD 205403B. The radii of HD 24465B and EPIC 211682657B have been measured by precise Kepler photometry and are consistent with theory within the error bars. However, the radii of SAO 106989B and HD 205403B, measured by KELT and STEREO photometry, are 17%-20% higher than those predicted by theory. A brief comparison of the results of the current work is made with the M dwarfs already studied in the literature.