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tokens: for its mass. Changing any parameter in a reasonable range does not lead to a consistent solution. As shown by Lorenz et al. ( 2005 ), the secondary of V1331 Aql reaches about 96% of the Roche radius. Thus, V1331 Aql exhibits a detached configuration, but the secondary is about to fill its Roche lobe. It was not possible to obtain a consistent age for the binary V413 Ser because of a disagreement on the HR diagram for all searched values of Z and α ov . V413 Ser is located in the Serpens star-forming region (Chavarria-K et al. 1988 ). The Serpens dark cloud contains an extremely young star cluster and most probably both components of V413 Ser are pre-main-sequence objects (Çakırlı et al. 2008 ) and not the main-sequence ones as we assumed in our age determination. Results for IM Mon, Ori V1388, and V380 Cyg will be presented below. IM Monocerotis : Till now, IM Mon was studied in detail only in two papers, i.e., Bakiş et al. ( 2010 ) and Bakis et al. ( 2011 ). In Bakis et al. ( 2011 ), the analysis of all available photometric and spectroscopic observations allowed them to determine the absolute values of masses: M A = 5.35(24) M and M B = 3.32(16) M , and radii: R A = 3.15(4) R and R B = 2.36(3) R . Moreover, it has been shown that IM Mon is a member of Ori OB1a association and the age of the system is about 11.5 Myr. The age was estimated from a comparison of the location of stars on the diagram with the isochrones of Girardi et al. ( 2000 ). A comparison of the observed high-resolution spectrum with Kurucz atmosphere models gave atmospheric parameters and metallicity [Fe/H] = +0.2. The age of IM Mon determined by Bakis et al. ( 2011 ) is in agreement with earlier determinations for Ori OB1a association by Blaauw ( 1991 ) and Brown et al. ( 1999 ). Using the masses and radii, we tried to re-determine the age of the system, as illustrated in Figure 9 . We found that metallicity of at least Z = 0.025 is needed to find a common age of the components that is in line with the values of [Fe/H] obtained by Bakis et al. ( 2011 ). Then, the age of the system is about 9.7(2.9) Myr, which is in agreement with the previous determinations. However, when we put the stars on the HR diagram (the bottom panel of Figure 9 ), it turned out that the secondary component is overluminous for its mass. The evolutionary tracks for the metallicity typical for galactic B-type stars, Z = 0.014, would be consistent, although marginal; but in this case, there is no common age for both components even if the large overshooting ( α ov = 0.5) is assumed for the primary star. One reason for that could be an effective temperature that is too high. The lower value of T eff would move the star to the right and down in the HR diagram. The second explanation could be a more complicated configuration of this binary, i.e., maybe the system is not fully detached or there is a third light. Figure 9. The similar plots as in Figure 6 but for components of IM Mon. V1388