English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

This paper presents a spectral and photometric study of the poorly studiedpolar BM CrB. Three states of the polar brightness and signs of transition fromone-pole to two-pole accretion mode were found by an analysis of ZTF data. Itis shown that the transition from the low state to the high state changes thelongitude of the main accretion spot (by $\approx 17^{\circ}$) and increasesits elongation (by $\approx 10^{\circ}$). The spectra contain Zeemanabsorptions of the H$\alpha$ line which are formed at a magnetic field strengthof $15.5\pm1$ MG. These absorptions are likely produced by a cold haloextending from the accretion spot at $\approx {^1/_4}$ of the white dwarfradius. Modeling of the behavior of the H$\alpha$ emission line shows that themain source of emission is the part of the accretion stream near the Lagrangianpoint L$_1$, which is periodically eclipsed by the donor star. The spectraexhibit a cyclotron component formed in the accretion spot. Its modeling by asimple accretion spot model gives constraints on the magnetic field strength$B=15-40$ MG and the temperature $T_e\gtrsim15$ keV.

Optical study of the polar BM CrB in low accretion state