At least four of nine candidate systems were reported to have magnetic white dwarfs. Three were considered very likely LARPs, the category sought in the search for wind-accreting pre-polars. A fourth was described as a normal polar undergoing Roche-lobe overflow, a different accretion arrangement from the wind-accreting pre-polars sought in the study. The magnetic tally does not mean that all four systems are wind-accreting LARPs.
The work set out to identify wind-accreting pre-polars among nine candidates, measure the magnetic fields of their white dwarfs and study the geometry of accretion. The candidates were selected from the Zwicky Transient Facility survey using unusual light-curve morphologies, colours and/or eclipse profiles. The sample was a targeted selection of unusual systems, not a general count of the wider population.
How the candidates were tested
Researchers used optical circular imaging photopolarimetry and circular spectropolarimetry. They also modeled cyclotron emission, a signal associated in the analysis with magnetic accretion, to estimate the white dwarfs' magnetic-field strengths. The methods addressed the stated goals of identifying wind-accreting pre-polars, measuring magnetic fields and studying accretion geometry.
The strongest magnetic signals
For three systems, the reported field estimates were about 40 MG for ZTF J0056+4926, about 110 MG for ZTF J2220+0721 with a question mark, and 54 MG for ZTF J2353+4153. The figures are model-derived estimates from cyclotron emission, and the question mark marks particular uncertainty around the J2220 value. J0056+4926 was also noted for strong, variable H-alpha emission.
ZTF J2353+4153 also offered a model-based view of accretion geometry. Cyclotron-map modeling suggested positive and negative accretion poles on approximately opposite sides of the white dwarf, along with a likely non-simple-dipole field geometry. The geometry is model-derived.
Some systems still resist a firm label
ZTF J1737+4013 was described as a clearly eclipsing polar, but its only spectrum had very low signal-to-noise and could not provide further insight.
ZTF J0504+2145 was considered likely to be a novalike CV, while the exact nature of other systems remained unclear. A possible 0.11-hour periodicity was not secure: the paper reported a 21% chance that the signal was not real and was produced by red noise or flickering. The period remains a tentative feature of the observations, not an established property of the system.
A targeted yield, not a census
The paper reports a confirmation rate of approximately one third for the search. The figure highlights both the promise and limits of variability-based pre-selection. The candidates were chosen for unusual light curves, colours and/or eclipse profiles. The nine systems were not a representative sample. The rate should not be read as a measure of how common LARPs are.
Partial orbital-phase coverage may have hidden accretion regions during some observations, leaving some classifications unresolved. This nine-system, selected sample is a source-level assessment rather than a statistically representative census.
The item is an arXiv version 1 preprint dated 26 August 2026. Appendix A includes ZTF light curves for all candidate sources.
Paper data and sources
Original title: Circular polarimetry of suspect wind-accreting pre-polars II
Authors: Pasi Hakala, Steven Parsons, Gavin Ramsay et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
Original paper · Full text