The first photometric and spectroscopic analysis of the extremely low mass-ratio contact binary NSVS 5029961

Abstract

ABSTRACT We performed photometric and spectroscopic investigations of NSVS 5029961 for the first time. The new BV(RI)c-band light curves were obtained with the 1.0-m telescope at Weihai Observatory of Shandong University. Applying the Wilson–Devinney program, we found that NSVS 5029961 is an A-subtype shallow contact binary with extremely low mass ratio (q = 0.1515, f = 19.1 per cent). Six spectra have been obtained by LAMOST, and many chromospheric activity emission line indicators were detected in the spectra, revealing that the target exhibits strong chromospheric activity. We calculated the absolute parameters with the photometric solutions and Gaia distance, and estimated the initial masses of the two components and the age of the binary. The evolutionary status was discussed by using the mass–radius and mass–luminosity diagrams. The result shows the primary component is a little evolved star and the secondary component has evolved away from the main sequence. The formation and evolution investigations of NSVS 5029661 indicate that it may have evolved from a detached binary with short period and low mass ratio by angular momentum loss via magnetic braking and case A mass transfer, and is in a stable contact stage at present.