Dramatic change of the recurrence time and outburst parameters of the intermediate polar GK Persei^*

Astronomical Institute, Academy of Sciences of the Czech Republic, 251 65 Ondřejov, Czech Republic

Corresponding author: V. Šimon, simon@asu.cas.cz

Received: 21 May 2001
Accepted: 25 October 2001

Abstract

This analysis has shown that the intermediate polar GK Per experienced a very striking evolution. Its outbursts became wider and brighter in the last five decades. These changes were accompanied by striking variations of the recurrence time T_C, from 385 days within the years 1948–1967 to 890 days in 1970. Nowadays, T _C displays a strong trend of linear increase. Decrease of irradiation of the disk by the WD, combined with the decrease of viscosity, offers a plausible explanation. It is argued that variations of the mass transfer rate are unlikely to play a major role. The morphology of the outburst light curves in the optical and the X-ray region is also studied. The decay branch in the optical remains remarkably similar for all the events while the largest changes of the light curve occur in the rising branch. This can be explained if the thermal instability may start at different distances from the disk center. The quiescent level of brightness does not display any secular trend in recent decades but a wave on the time scale of about 30 years with the full amplitude of 0.3 m_v, probably due to activity of the cool star, is detected.