Magnetic-field constraints for four magnetic cataclysmic variables from simultaneous continuum and cyclotron modeling

Abstract

their 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. We fit a white dwarf atmospheric model, a hot-spot blackbody, and an isothermal constant-$\Lambda$ cyclotron component in one inverse-variance weighted model. Profiling chi-square 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, 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, $B=56.8\pm 1.5$ MG, for J0005+2941. J0022+1340 has two indistinguishable branches at $B\simeq 64.4$ and 77.7 MG; J0749+3654 has competitive solutions near 29.3 and 96.4 MG; and J0035+4333 yields an indicative broad minimum at $B=51.1\pm 1.4$ MG. The ZTF data give 105.349 min for J0005+2941, with a narrow eclipse-like minimum, making it a rare eclipsing-polar candidate below the period gap; 80.4062 min for J0749+3654 from double-humped cyclotron beaming; and 143.8 min for J0035+4333. Strong He II 4686 in J0022+1340 and J0035+4333 and flat-to-inverted Balmer decrements in all four support magnetically channeled accretion. Archival mid-infrared photometry excludes donors earlier than about M4.5-M5 V in three systems and M3 V in J0035+4333. Joint continuum-cyclotron fitting gives secure fields when the humps are well resolved and explicit branch constraints otherwise.

arXiv commentAccepted for publication in A&A. 22 pages, 11 figures