Long-period eclipsing binaries: towards the true mass-luminosity relation. II. Absolute parameters of the NN Del system

We present results of our study of the long-period eclipsing binary star NN Delphini (hereafter NN Del). The results are based on spectral data obtained with the HRS échelle spectrograph of the Southern African Large Telescope (SALT). Our constructed velocity curve is based on 19 spectra obtained between 2017 and 2019 years and covers all phases of the binary's orbit. The orbital period, P =99.252 days, was determined from our spectral data and coincides with the period determined in previous studies, as well as the system eccentricity of e =0.517 . Calculated velocity amplitudes of both components allow us to determine the masses of both system components M₁=1.320 M_⊙ and M₂=1.433 M_⊙ with the accuracy about of one percent (0.8% and 1.1%), respectively. Luminosities of both components are presented as L₁=4.164 L_⊙ and L₂=6.221 L_⊙, and the effective temperatures of both components were directly evaluated (T_{e f f 1}=6545 K and T_{e f f 2}=6190 K) together with the metallicity of the system [F e /H ] =-0.19 dex and its color excess E(B-V) = 0.026 mag. Comparison with evolutionary tracks shows that the system age is 2.25 ±0.19 Gyr, and both components are on the main sequence and have not yet passed the turn point. Spectral type is F5V for the hotter component and F8V for another one.