A rare low state of the intermediate polar BG CMi
ATel #17050; Colin Littlefield (BAER Institute), Michel Bonnardeau (MBCAA Observatory), Peter Garnavich (University of Notre Dame)
on 24 Feb 2025; 21:31 UT
Credential Certification: Colin Littlefield (clittlef@alumni.nd.edu)
Subjects: Optical, Cataclysmic Variable
Referred to by ATel #: 17089
The eclipsing intermediate polar BG Canis Minoris (BG CMi) is currently in a rare low state. First noticed by coauthor M. Bonnardeau, this low state appears to be the first in the observational history of BG CMi. Photometry from the Asteroid Terrestrial-impact Last Alert System (ATLAS; Tonry et al. 2018, PASP, 130, 064505) and the database of the American Association of Variable Star Observers (AAVSO) shows that the fading began on approximately 2025 January 13 and that the depth of the low state is approximately 0.5 magnitudes in the optical.
We have obtained time-series photometry of BG CMi using the University of Notre Dame's 0.8-m Sarah L. Krizmanich Telescope and combined it with time-series photometry from the AAVSO. Power spectral analysis of these data shows that the amplitude of the white dwarf's spin frequency (f_spin) is significantly lower during the low state than it was prior to the low state. Additionally, the amplitude of the f_spin - 2*f_orbit sideband frequency (where f_orbit denotes the binary orbital frequency) is greatly enhanced relative to that of f_spin during the low state. These observations suggest that there have been significant physical changes to the system's accretion processes during the low state.
We encourage time-series photometry of BG CMi during this low state with the aim of monitoring the evolution of its optical power spectrum. Even during its low state, BG CMi is suitably bright (V~15.5) to be monitored by amateur astronomers.
