Masses and Radii of Four Very Low-mass Stars in F plus M Eclipsing Binary Systems

Eclipsing Binaries (EBs) with one of the companions as very low mass stars (VLMS 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, KELT, Kepler 2 (K2) and STEREO. Using the high-resolution spectrograph, PARAS, at the 1.2 m telescope at Mount Abu, Rajasthan, India, we hereby report the detection of four VLMS 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-circle dot for SAO 106989, HD 24465, EPIC 211682657 and HD 205403 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 radius derived by modeling the photometry data are 0.326 +/- 0.012 R-circle dot for SAO 106989, 0.244 +/- 0.001 R-circle dot for HD 24465, 0.566 +/- 0.005 R-circle dot for EPIC 211682657, and 0.444 +/- 0.014 R-circle dot for HD 205403. The radii of HD 24465B and EPIC 211682657B have been measured by precise KEPLER photometry and are consistent with theory within 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 literature.