Kolbin A.I., Suslikov M.V., Kochkina V.Yu., Borisov N.V., Burenkov A.N., Oparin D.V. (SAO RAS)

    Polars are close binaries consisting of an accreting magnetic white dwarf (hereinafter referred to as a WD) and a cool donor star (usually an M dwarf). The strong magnetic field of a WD (10-100 MG) makes these systems synchronous, i.e., leads to equality of the WD rotation period P_spin and the orbital period P_orb. However, among the polars, there is a small group of asynchronous polars (8 systems with candidates are known) exhibiting asynchrony <3%. The nature of the asynchrony remains unclear, but it has been suggested that it may be due to the recent Nova explosion. Our work has supplemented the list of asynchronous polars with the system SDSS J085414.02+390537.3. We discovered its asynchrony from the analysis of ZTF photometry, in which different periods Porb and Pspin are distinguished as well as the beat period P_beat (1/P_beat = 1/P_orb - 1/P_spin). The corresponding polar asynchrony is 0.3%. The system shows signs of a change in the main accreting pole, which are difficult to detect in previously known systems. The spectra of the polar obtained at the BTA telescope with the SCORPIO-1 and -2 instruments demonstrate Zeeman splitting of hydrogen lines and cyclotron harmonics, the modeling of which gives an estimate of the WD magnetic field B = 28-34 MG.

Fig. 1. Shift of the bright phase during the beat period (left) and a model of changing the accreting pole (right) interpreting this phenomenon.

Fig. 2. Determination of the average magnetic field of the WD by Zeeman splitting of the Hβ line.

The work was supported by the grant of the Russian Science Foundation № 22-72-10064.

Published:
Kolbin A.I., Suslikov M.V., Kochkina V.Yu., Borisov N.V., Burenkov A.N., Oparin D.V., SDSS J085414.02+390537.3 – a new asynchronous polar, 2023, Astronomy Letters, Volume 49, Issue 8, p. 475–485, DOI: 10.1134/S1063773723080029