Global parameters of the W UMa stars FI Lyn, UV Lyn, and NSVS 781878

Photometric and spectral observations of the W UMa binaries FI Lyn, UV Lyn, and NSVS 781878 with periods of around 9.5–10 hr were carried out in order to determine their global parameters by simultaneous light curve and radial velocity curve solutions. We found that the three targets have shallow‑contact configurations with close in mass and radius components. UV Lyn is of W‑subtype, NSVS 781878 is of A‑subtype, while FI Lyn may be considered as binary in thermal contact. Our data show evidences of photospheric activity of the targets but not of emission in the Hα line. The surface inhomogeneity of UV Lyn is stable during the last several decades. Its O–C diagram implies presence of third body with a period of 24 years. The distances of FI Lyn, UV Lyn, and NSVS 781878 calculated from the derived luminosities coincide with those obtained by GAIA astrometrically.