We present results of our study of the longperiod 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 (Teff1 = 6545 K and Teff2 = 6190 K) together with the metallicity of the system [Fe/H] = −0.19 dex and its color excess E(BV)=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.

中文翻译：

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长周期食双星：走向真正的质光关系。二、NN Del系统的绝对参数

我们展示了我们对长周期食双星 NN Delphini（以下简称 NN Del）的研究结果。结果基于使用南部非洲大型望远镜 (SALT) 的 HRS 中阶梯光栅光谱仪获得的光谱数据。我们构建的速度曲线基于 2017 年至 2019 年间获得的 19 个光谱，涵盖了双星轨道的所有阶段。轨道周期 P = 99.252 天，是根据我们的光谱数据确定的，与之前研究中确定的周期以及系统偏心率 e = 0.517 一致。计算出的两个分量的速度幅度使我们能够确定两个系统分量 M1 = 1.320 M 和 M2 = 1.433 M 的质量，准确度分别约为 1%（0.8% 和 1.1%）。两个组件的光度表示为 L1 = 4.164 L 和 L2 = 6.221 L，并且直接评估了两种组分的有效温度（Teff1 = 6545 K 和 Teff2 = 6190 K）以及系统的金属丰度 [Fe/H] = -0.19 dex 及其颜色过量 E(BV) = 0.026 mag。与演化轨迹对比表明，系统年龄为2.25±0.19 Gyr，两个分量都在主序带上，尚未通过转折点。较热组件的光谱类型为 F5V，另一组件为 F8V。