Description
Cataclysmic Variables (CVs) are close binaries in which a white dwarf is accreting from a donor star that fills its Roche lobe. Whilst the evolution of CVs is an important subject they are also the natural laboratory for studying accretion in other less accessible objects.
The number of confirmed CVs continues to grow thanks particularly to large-scale photometric, spectroscopic and x-ray surveys projects such as ZTF, SDSS,DESI and eRosita.
Whilst analysing over 1700 CV spectra from SDSS and DESI a small proportion ($<1\%$) were found that exhibited peculiar short-term variations in luminosity and by inference accretion. The spectroscopy suggests that these systems are at most weakly magnetic and that they have low accretion rates as both the white dwarf and donor are visible, hence a dwarf nova-like behaviour with recurrent thermal disc instabilities is expected. However the light curves display erratic long-term variability with the systems meandering between a faint and a bright state, similar to the light curves of strongly magnetic CVs (polars). The cause of these long-term variations is currently not understood, and it is not clear how these systems fit into the overall evolutionary model.
