Spectral Types of Long-Period Double-Lined Eclipsing Binary System Components from Low-Resolution Spectroscopy Data

We present the results of spectral observations and consequent analysis of six long-period double-lined eclipsing binaries (DLEBs) with main-sequence (MS) components from a sample formed with the aim of testing the ‘‘mass–luminosity’’ relation (MLR) for stars in the M/M_⊙>1.5 mass range. We analyzed all the obtained spectra using a technique that allows one to reveal the binary nature of the system and determine T_eff and log g for each component, as well as the system metallicity [Fe/H] and line-of-sight extinction E(B-V) . We computed the absolute parameters of the systems under consideration. An analysis of the obtained spectra shows that for three of the six objects (V1156 Cyg, EU Gem and V733 Per) we can clearly establish their binary nature and determine the spectral type and class for each component. Both components of the V733 Per system have already left the MS, and therefore the system must be excluded from our sample, whereas studies of V1156 Cyg and EU Gem should continue. OT And did not demonstrate a binary spectrum, however, the main component of the system is a hot A6 V star, and therefore, OT And should remain in our sample. We also revealed no binarity in the IM Del and LX Gem systems. Their brighter components turned out to be a cool giant and a supergiant, and these systems should be excluded from the sample based on the results of our analysis. We used the same technique to analyze the two spectra obtained for systems EU Gem and LX Gem using LAMOST. We have shown that the parameters determined from LAMOST spectra are in good agreement with the parameters determined for spectra obtained at the Caucasian Mountain Observatory (CMO) of SAI MSU. Our analysis allowed us to plot a first approximation of the V1156 Cyg velocity curves and show that the cool component in this system has a larger mass.