Magnetic-field constraints for four magnetic cataclysmic variables from simultaneous continuum and cyclotron modeling
Year: 2026
Type: article
Abstract: Wide-field spectroscopic surveys are finding magnetic cataclysmic variable (CV) candidates, but their magnetic fields are rarely measured because cyclotron humps must be separated from uncertain continua and assigned to discrete harmonics. We applied a simultaneous continuum--cyclotron analysis to four DESI/LAMOST magnetic-CV candidates, aiming to determine or bound their fields and measure their periods. We fit a white dwarf atmospheric model, a hot-spot blackbody, and an isothermal constant-Λ cyclotron component in one inverse-variance weighted model. Profiling the chi-square goodness of fit over the field strength exposes competing harmonic assignments, which we report as multiple acceptable branches when necessary, and posterior sampling gives branch-conditional uncertainties. We validated the field recovery on EQ Cet, BS Tri, and three SDSS polars with published fields, searched 6--7 yr of ZTF photometry for periods and aliases, and used archival UV-to-mid-infrared photometry to bound the donors. The fit gives one robust field, B = for J0005$+$2941. The remaining spectra are less decisive: J0022$+$1340 has two indistinguishable branches at B ≃ 64.4 and 77.7,MG; J0749$+$3654 has competitive solutions near 29.3 and 96.4,MG; and J0035$+$4333 yields an indicative single but broad minimum at B = 51.1 The ZTF data give 105.349,min for J0005$+$2941, with a narrow eclipse-like minimum, making it a rare short-period eclipsing-polar candidate; 80.4062 for J0749$+$3654 from double-humped cyclotron beaming; and 143.8,min for J0035$+$4333. Line diagnostics show strong He,II łambda4686 in J0022$+$1340 and J0035$+$4333 and flat-to-inverted Balmer decrements in all four, consistent with magnetically channeled accretion. Archival mid-infrared photometry excludes donors earlier than about M4.5--M5,V in three of the systems and donors earlier than about M3,V in J0035$+$4333. We thus measure or bound the field of every target and identify J0005$+$2941 as a rare eclipsing-polar candidate below the period gap. Joint continuum--cyclotron fitting gives secure fields when the humps are well resolved and explicit branch constraints otherwise.
Source: Astronomy and Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, California Institute of Technology, National Natural Science Foundation of China, National Development and Reform Commission, National Astronomical Observatories, Chinese Academy of Sciences, Lawrence Berkeley National Laboratory
OpenAlex ID: W7223010195