Parameter Determination for the Eclipsing Long-Period Dwarf Nova EX Dra from Photometric Observations during Different Activity States of the System
Abstrakt
The results of a long-term photometric observations of the cataclysmic variable EX Dra acquired between 2014 and 2016 at the Crimean Station of the Sternberg Astronomical Institute (24 nights, more than 10 500 measurements) are presented. The observations were performed using CCD photometers mounted on 50-cm and 60-cm telescopes in the visible and red, during both quiescence and the active state.
For completeness, photometric observations obtained at the Ondrejov Observatory in 2010 in the V and R Johnson filters are also used in the analysis. The new observations of EX Dra are used to derive the orbital period of the system, which agrees well with earlier determinations.
A combined model that takes into account the radiation fluxes from the gaseous stream and a hot spot on the lateral surface of the accretion disk is used to determine the parameters of the system components (white dwarf, red dwarf, accretion disk and hot spot, and gaseous stream). Variations of the parameters when the system changes from one activity state to the other are considered.
Six light curves displaying unsatisfactory agreement between the observed and theoretical light curves can be successfully fitted using a version of the combined model that includes hot spots on the secondary's surface. This model is able to qualitatively reproduce a secondary minima in the light curves that exhibits shifts of this minimum from phase 0.5.
The parameters of dark spots on the red-dwarf surface were determined. The data obtained indicate that the outbursts in the EX Dra system are related to instability of the matter outflow from the secondary.