Ground- and space-based investigation of the intermediate-age open star cluster NGC 2126

We performed ground-based, time-series observations of the intermediate-age open cluster NGC 2126 with the 1.3-meter Devasthal Fast Optical Telescope (ARIES) and discovered 112 variable stars in an 18 x 18 arcmin field. Among these, 11 stars were known variables, for which we performed TESS full-frame image photometry in three different sectors. There were 17 new member variables and 84 variable field stars. The eclipsing binary V551 Aur is a member of NGC 2126 with high probability and has a pulsating component. This star was studied in detail by means of a medium-resolution spectrum and TESS photometry. The light curve was analyzed using a binary model, which was then removed to investigate the pulsational variability. The new variable members were classified based on their position in the HR diagram, shape of the phase-folded light curves, period and amplitude of variability. We also modeled the light curves of other binary stars in the field to determine their orbital parameters.