First multi-colour photometric study of the short period K-type contact binary NSVS 2701634

• We present the first multi-color light curve analysis of the eclipsing binary star NSVS 2701634.
• The orbital period variation are studied for the first time.
• The system belong to the W-subtype W Ursae Majoris systems.
• Its spectral type K makes interesting this study on NSVS 2701634.
• Both the components of NSVS 2701634 follow the general pattern of the W-subtype systems in the logM-logL diagram.

We present the first CCD sets of complete light curves for the W Ursae Majoris W-type system NSVS 2701634. The observations were performed in the B, V and Ic bands using the 0.25 m telescope of the “Stazione Astronomica Betelgeuse” Italy, during 8 nights in April 2015.From our observations we were able to confirm and revise the short-period (0.24 days) variation found by Shaw and collaborators in their online list (http://physast.uga.edu/~jss/nsvs/) of periodic variable stars found in the Northern Sky Variability Survey.Using our 12 times of minimum light, the orbital period variations of NSVS 2701634 are studied for the first time. The general trend of the (O-C) curve reveals that its period is varying by a downward parabola that means that period is decreasing, this fact could be explained by a mass transfer between the components of the system.The light curves were modelled using the Wilson–Devinney code and the elements obtained from this analysis are used to compute the physical parameters of the system in order to study its evolutionary status.A reasonable fit of the synthetic light curves of the data indicated that NSVS 2701634 is an late-type (K3−−K4+K6) contact binary system of W-Subtype of the W Ursae Majoris systems, with a mass ratio of q = 2.60, a degree of contact factor f = 15.3% and inclination i = 72°. The light curves show asymmetries at the maxima that are fitted adding an hot spot on the surface of the more massive star, known as inverse O’Connell effect.From an estimation of the absolute dimensions of the system and from the logM-logL diagram, it is seen that both components of NSVS 2701634 follow the general pattern of the W subtype W Ursae Majoris systems.