The Rise and Fall of the King: The Correlation between FO Aquarii’s Low States and the White Dwarf’s Spin-down

Abstract

The intermediate polar FOAquarii (FO Aqr) experienced its first reported low-accretion states in

An accreting white dwarf displaying fast transitional mode switching

“…3). Although the ASAS-SN lightcurve indicates that TW Pic can undergo slow transitions from a high to a low state (and vice versa) on timescales of weeks to months as is observed in several other accreting white dwarfs 1,19,20 , the moding behaviour occurring on ≈30 minute timescales appears to be restricted to the more recent observations. The TESS Cycle 3 data also reveal the mode switching from the low to the high mode, occurring on a somewhat longer timescale of ≈12 hours (see Extended Data Fig.…”

“…This suggests that the optical emission of TW Pic, at that epoch, was due to the bare white dwarf and secondary star photospheres and hence that accretion was turned off. Furthermore, the ROSAT All Sky survey observed TW Pic between Aug. [12][13][14][15][16][17][18][19][20][21][22]1990 and between Feb. [13][14][15]1991. From inspection of the X-ray light curve of TW Pic, provided in the Second ROSAT X-ray Source (2RXS) catalogue products 42 , the source is not significantly detected in August, while it is detected at the 4σ level in February, further supporting that accretion switched off in August 1990.…”

“…The rapid moding timescale and large luminosity drop both indicate that the origin is associated with a sudden reduction in the mass accretion rate onto the white dwarf. Changes from high to low states and vice versa have been observed in the so-called novalikes, including magnetic systems, as well as in VY Scl stars, but occurring on much longer (days to months) timescales where the mass transfer rate from the companion almost, or totally, turns off 14,19,20,22 . The rapid transitions displayed in TW Pic have never been observed in an accreting white dwarf, suggesting a different mechanism regulating the mass accretion rate between the two modes.…”

Optical detection of the rapidly spinning white dwarf in V1460 Her

“…IPs have spin periods of order minutes to tens of minutes (Patterson 1994). These are rates much slower than breakup, but faster than their binary periods, reflecting a quasi-equilibrium between spin-up and magnetic drag that is con-tinuously adjusting to a fluctuating accretion rate (Patterson 1984;Kennedy et al 2016;Littlefield et al 2020) Not all systems exist in quasi-equilibrium. One of the first recognised cataclysmic variables, AE Aquarii, shows remarkable flaring behaviour that is thought to be driven by magnetically-propelled material exiting the system (Wynn et al 1997).…”

Quasi-periodic Oscillations in the TESS Light Curve of TX Col, a Diskless Intermediate Polar on the Precipice of Forming an Accretion Disk

“…The mode of accretion in a particular IP can change in response to variations in the system's mass-transfer rate (M  ). FO Aqr, which shows disk-fed accretion when M  is highest and some form of stream-fed accretion when M  decreases (Littlefield et al 2020), is perhaps the best example of this phenomenon. Overall, disk-fed accretion tends to be the most commonly observed mode of accretion in the majority of IPs.…”