Resynchronization of the Asynchronous Polar CD Ind

Abstract

CD Ind is one of only four confirmed asynchronous polars (APs). APs are strongly magnetic cataclysmic variables of the AM Herculis subclass with the characteristic that their white dwarfs rotate a few per cent out of synchronism with their binary orbit. Theory suggests that nova eruptions disrupt previously synchronized states. Following the eruption, the system is expected to rapidly resynchronize over a timescale of centuries. The other three asynchronous polars -V1432 Aql, BY Cam and V1500 Cyg -have resynchronization time estimates ranging from 100 to more than 3500 years, with all but one being less than 1200 years. We report on the analysis of over 46000 observations of CD Ind taken between 2007 and 2016, combined with previous observations from 1996, and estimate a CD Ind resynchronization time of 6400 ± 800 years. We also estimate an orbital period of 110.820(1) minutes and a current (2016.4) white dwarf spin period of 109.6564(1) minutes.

TESS observations of the asynchronous polar CD Ind: mapping the changing accretion geometry

“…The full light curve shows variability on many different timescales, the most obvious being the repeating features every ∼7.3 days. The variation in the flux corresponds to ∼2.5 mag, which is comparable with the variation found by Myers et al (2017). In Figure 2 we show the light curve covering the first beat cycle.…”

“…In our following analysis we have assumed P or b = 110.8124 min and P spin = 109.6525 min (Myers et al 2017), which imply a beat period of 7.3 d. It should be noted, that the orbital period value (110.82005 min) quoted in (Myers et al 2017) is not compatible with the value implied by their quoted orbital frequency (110.81237 min). Moreover, their quoted spin frequency (13.1324 cyc/d, section 3.3) is not in agreement with the spin period quoted in section 3.1 (109.6564 min).…”

“…The brightness of CD Ind varies considerably over the beat cycle. Myers et al (2017) report observations of CD Ind made over ten years which show a white light magnitude in the range 15.5-18.5 mag and will therefore show a lower signal-to-noise than most of the targets which are be-ing searched for exo-planets, the faintest being I ∼ 13 (Ricker et al 2015). Each full-frame image is downloaded every 30 min.…”

“…For our purposes, we have adopted the orbital and spin periods of CD Ind as determined by Myers et al (2017) as a basis of our simulations. Furthermore, we have assumed M 2 =0.21M based on the orbital period and M 1 =0.7M leading to the mass ratio q=0.3.…”

“…The latter also first identified it as a possible short period asynchronous polar with the white dwarf having a magnetic field of 11±2 MG. Optical polarimetry and X-ray observations Ramsay et al (1999Ramsay et al ( , 2000 confirmed CD Ind as an asynchronous polar with a beat period of approximately a week. Using ten years of data, Myers et al (2017) determined an orbital period of 110.812 min and a white dwarf spin period of 109.652 min, giving a beat period of 7.299 d, making it the asynchronous polar with the shortest beat period. It is therefore the most useful system to more easily study the interaction of an accretion stream with a rotating magnetic field.…”