Study of the period changes in SW Dor, an RR Lyrae type star with Blazhko effect

Abstract

In 2012–2014 we acquired 1569 CCD BVIc frames for the RR Lyrae type variable SW Dor with the 76-cm telescope of the South African Astronomical Observatory (SAAO) and 1-m telescopes of Las Cumbres Observatory Global Telescope network (LCOGT). Our observations showed a large scatter in the resulting phased light curve, especially near maximum brightness, which allowed us to reveal the Blazhko effect with a period of ∼80.d9. To study the pulsation period changes, we used all the available observations including the 1299 magnitude estimates from the digitized plate library of Harvard University (the DASCH project), which allowed us to construct the O−C diagram spanning a 125-year long time interval and discover for the first time at least three abrupt changes of the pulsation period.