NSVS 2569022: a peculiar binary among the W UMa stars with extremely small mass ratios

Abstract

Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type (temperatures $T_1$=$T_2$=6100 K). NSVS 254037 undergoes total eclipse of W subtype and the mass ratio is well-determined. Its exclusive small value of only 0.077 implies that the target probably goes to instability and possible merger. This value ranks NSVS 2569022 in sixth place among the binaries with smallest mass ratio. On the base of empirical relation "period -- total mass" for low mass-ratio binaries we estimated the global parameters of NSVS 2569022: masses $M_1$=1.17 M$_{\odot}$ and $M_2$=0.09 M$_{\odot}$; radii $R_1$=1.19 R$_{\odot}$ and $R_2$=0.38 R$_{\odot}$; luminosities $L_1$=1.73 L$_{\odot}$ and $L_2$=0.17 L$_{\odot}$. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out peculiar binary among the W UMa stars with extremely small mass ratios due to its unexpected small fill-out factor of only 0.014 (slightly overcontact configuration).