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

TL;DR

This study precisely determines the absolute parameters of the long-period eclipsing binary NN Del, including masses, luminosities, and temperatures, contributing to the understanding of the mass-luminosity relation for such systems.

Contribution

It provides accurate measurements of the system's parameters using SALT spectral data, enhancing the empirical data for long-period eclipsing binaries.

Findings

Masses determined with ~1% accuracy

System age estimated at 2.25 Gyr

Both stars are on the main sequence

Abstract

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 echelle 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 M_1 = 1.320 M_sun and M_2 = 1.433 M_sun with the accuracy about of one percent (0.8% and 1.1%), respectively. Luminosities of both components are presented as L_1 = 4.164 L_sun and L_2 = 6.221 L_sun, and the effective temperatures of both components were directly evaluated (T_eff = 6545~K and T_eff = 6190~K) together with the metallicity of the system [Fe/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.