The article by Vojtěch Šimon from the Stellar Department of ASU focuses on two specific polars: BY Camelopardalis (BY Cam) and AR Ursae Majoris (AR UMa). Both objects belong to the same category, but exhibit completely different long-term activity patterns. The author used extensive data from modern survey projects (Zwicky Transient Facility, Catalina Real-time Transient Survey) and historical photographic archives (digitized DASCH photographic plates). This provided him with time series covering decades, allowing him to subject the light curves to detailed analysis. The result is a detailed comparison that provides new insights into how variable and diverse mass accretion can be in magnetic cataclysmic variables.
Abstract
Polars are cataclysmic variables with strongly magnetized white dwarfs (WDs). This analysis of the long-term optical activity of two polars (BY Cam and AR UMa) used the light curves of CCD data from the ZTF and CRTS and photographic data from the DASCH databases. These two polars display remarkably discrepant long-term activities. The high-state activity dominated BY Cam, except for a short and shallow low-state episode. A fit to BY Cam’s light curve shows long-term brightness changes in the high state. We ascribe the variable profiles of the histograms of the residuals of this fit (1-year bins) to the changes in the dominance of the individual accretion modes and accreting regions on the WD with time (hundreds of days). The high-state episodes (no matter how long and bright) of AR UMa occurred from a relatively stable low-state brightness level. The superorbital changes of AR UMa dominated in the high states. Bursts of mass transfer from the donor are likely to contribute to the short high-state episodes.
more in popular article: web ASU (in Czech)
Image description: Polar in an illustration created by generative artificial intelligence based on data from the article. Created using OpenAI DALL-E.
More information
- source: Na čem pracujeme: Odlišné chování polarů BY Cam a AR UMa (M. Švanda, web ASU, popular article in Czech)
- V. Šimon, The discrepant long-term activities of the polars BY Camelopardalis and AR Ursae Majoris, New Astronomy 118 (2025) id.10375
- contact: RNDr. Vojtěch Šimon, Ph.D., simon@asu.cas.cz
