Dwarf Spin Period Research Articles

Periodic eclipse variations in asynchronous polar V1432 Aql: evidence of a shifting threading region

We report the results of a 28-month photometric campaign studying V1432 Aql, the only known eclipsing, asynchronous polar. Our data show that both the residual eclipse flux and eclipse O−C timings vary strongly as a function of the spin-orbit beat period. Relying upon a new model of the system, we show that cyclical changes in the location of the threading region along the ballistic trajectory of the accretion stream could produce both effects. This model predicts that the threading radius is variable, in contrast to previous studies which have assumed a constant threading radius. Additionally, we identify a very strong photometric maximum which is only visible for half of the beat cycle. The exact cause of this maximum is unclear, but we consider the possibility that it is the optical counterpart of the third accreting polecap proposed by Rana et al. Finally, the rate of change of the white dwarf's spin period is consistent with it being proportional to the difference between the spin and orbital periods, implying that the spin period is approaching the orbital period asymptotically.

DISCOVERY OF POLARIZED EMISSION FROM TWO SOFT X-RAY-EMITTING INTERMEDIATE POLARS: UU Col AND NY Lup

We aim to investigate the magnetic field strengths and cyclotron emission of the two soft X-ray-emitting intermediate polars (IPs) UU Col and NY Lup. We study the connection between polars and soft X-ray-emitting IPs by searching for evidence of circularly polarized light in these two systems, which may be examples of progenitors of polars. We carried out photopolarimetric observations of our targets using the Very Large Telescope (UT2) and FORS1 at Paranal. Imaging polarimetry with good signal-to-noise and relatively high time resolution is possible for these targets using such a large telescope. Detection of circular polarization, modulated according to a white dwarf (WD) spin period, is clear evidence of cyclotron emission processes near the WD surface. The color dependence of the polarization allows us to make estimates of the magnetic field strength. We found that both UU Col and NY Lup emit circularly polarized light in the B and I bands, modulated at the spin period of the WD in each case. We add further confirmation to the idea that soft X-ray-emitting IPs emit circularly polarized light and that cyclotron emission plays an important role in these systems. This also suggests that some soft X-ray-emitting IPs might be progenitors of polars.

The pulsations of AE Aqr: spin or beat?

The cataclysmic variable star AE Aqr pulsates coherently on a period of 33.08 s at both optical and X-ray wavelengths. The pulses, which originate from the rotation of an accreting, magnetic white dwarf, show a variable delay in their time of arrival as the binary rotates. Reprocessing of extreme ultraviolet and X-ray radiation off a target fixed in the rotating frame of the binary has been suggested to explain the delays, which, as recent observations show, cannot be simply ascribed to the orbital motion of the white dwarf. If this is so, the pulsations occur on the beat period between the white dwarf's spin period and the binary's orbital period