OY Carinae
OY Carinae is an eclipsing binary star system in the southern constellation of Carina, abbreviated OY Car. It is located at a distance of approximately 296 light-years from the Sun, and is classed as a cataclysmic variable. The system comprises a double eclipsing white dwarf and red dwarf that orbit each other every 1.51 hours, and possibly a yet unconfirmed third low-mass companion.
Observations
discovered that the star is a cataclysmic variable, in 1959. In 1976, it was identified as a candidate SU Ursae Majoris -type variable. It was found to be a double eclipsing binary system by Nikolaus Vogt in 1979, who determined a period of 91 minutes. This behavior potentially allows for precise determination of the physical parameters of the system. Superhumps during an outburst of OY Car were reported in 1980, confirming its status as an SU UMa variable.The standard model for this type of system has a cool star orbiting a compact white dwarf. The cool star is filling its Roche lobe and is feeding matter to an accretion disk orbiting the white dwarf. The eclipsing of the accretion disk allows its dimensions to be estimated. The impact point of the material contacting the accretion disk produces a "hot spot", which is responsible for the superhump feature in the light curve.
By 1991, superoutbursts of OY Car were found to occur on an almost annual cycle, with a mean time interval of 346.5 days. However, individual cycles could range from 354 to 472 days. The mean maximum magnitude was 11.45, with the system being above magnitude 13 for an average of 12 days. These superoutbursts are thought to occur during periods of rapid accretion onto the white dwarf, which in SU UMa systems can be triggered by tidal resonances in the disk. During a superoutburst, the temperature of the white dwarf can increase to before steadily declining.
As material accretes onto the white dwarf it undergoes decelaration and emits X-rays. However, the high inclination of the system means that this emission is obscured by the disk. Most of the X-ray emission from OY Car appear to come from the polar regions. This suggests the accretion is magnetically directed onto the pole of an inclined dipolar field.
Planetary system?
Greenhill et al. would invoke the presence of a third object to explain orbital period variations with an apparent periodicity of roughly 35 years. The third body could yield a minimum mass 7 times greater than Jupiter and be located 9.5 astronomical units away from the cataclysmic variable system, being likely either a massive planetary object or else a very low-mass brown dwarf.It is likely that the apparent change is due to solar cycle type magnetic activity in the secondary star. Large irregular deviations from the general trend, with time-scales of years, also occur. Further observations will be able to confirm or disprove the presence of a substellar companion.