Study of orbital period variation in DK Cyg using extended eclipse timing data

We present an updated orbital period analysis of the contact binary system DK Cyg using new and archived mid-eclipse times. A total of 201 new mid-eclipse times were derived from high-precision Transiting Exoplanet Survey Satellite (TESS) observations, complemented by 37 additional timings from the VarAstro database and previously published data. These data extend the observed-minus-calculated ((Formula presented) ) diagram by nearly nine years, enabling a more comprehensive investigation of the orbital evolution of the system. A revised quadratic ephemeris confirms a continuous period increase, consistent with earlier studies and likely driven by mass transfer. To search for potential periodic modulations, we applied both the Lomb–Scargle periodogram and the Weighted Wavelet Z-transform (WWZ). While both methods indicate a possible long-period signal, this variation appears to originate primarily from older data and is not supported by the more recent eclipse timings. In addition, the light travel time (LTT) model previously proposed in the literature was tested and found to be incompatible with the updated eclipse times. Our results showed that while the quadratic model reasonably fits the overall trend in the updated (Formula presented) diagram, the nature of the residual variations remains uncertain. It is not yet clear whether these residuals are indicative of a LTT effect or simply statistical fluctuations. Therefore, further eclipse timing observations are needed to clarify the long-term orbital behavior of DK Cyg.