The Rise and Fall of the King: The Correlation between FO Aquarii’s Low States and the White Dwarf’s Spindown. (arXiv:1904.11505v1 [astro-ph.SR])

The Rise and Fall of the King: The Correlation between FO Aquarii’s Low States and the White Dwarf’s Spindown. (arXiv:1904.11505v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Littlefield_C/0/1/0/all/0/1">Colin Littlefield</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garnavich_P/0/1/0/all/0/1">Peter Garnavich</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kennedy_M/0/1/0/all/0/1">Mark R. Kennedy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Patterson_J/0/1/0/all/0/1">Joseph Patterson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kemp_J/0/1/0/all/0/1">Jonathan Kemp</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stiller_R/0/1/0/all/0/1">Robert A. Stiller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hambsch_F/0/1/0/all/0/1">Franz-Josef Hambsch</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Heras_T/0/1/0/all/0/1">Teofilo Arranz Heras</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Myers_G/0/1/0/all/0/1">Gordon Myers</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stone_G/0/1/0/all/0/1">Geoffrey Stone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sjoberg_G/0/1/0/all/0/1">George Sjoberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dvorak_S/0/1/0/all/0/1">Shawn Dvorak</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nelson_P/0/1/0/all/0/1">Peter Nelson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Popov_V/0/1/0/all/0/1">Velimir Popov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bonnardeau_M/0/1/0/all/0/1">Michel Bonnardeau</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vanmunster_T/0/1/0/all/0/1">Tonny Vanmunster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miguel_E/0/1/0/all/0/1">Enrique de Miguel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Alton_K/0/1/0/all/0/1">Kevin B. Alton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harris_B/0/1/0/all/0/1">Barbara Harris</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cook_L/0/1/0/all/0/1">Lewis M. Cook</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_K/0/1/0/all/0/1">Keith A. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brincat_S/0/1/0/all/0/1">Stephen M. Brincat</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lane_D/0/1/0/all/0/1">David J. Lane</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Foster_J/0/1/0/all/0/1">James Foster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pickard_R/0/1/0/all/0/1">Roger Pickard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sabo_R/0/1/0/all/0/1">Richard Sabo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vietje_B/0/1/0/all/0/1">Brad Vietje</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lemay_D/0/1/0/all/0/1">Damien Lemay</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Briol_J/0/1/0/all/0/1">John Briol</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krumm_N/0/1/0/all/0/1">Nathan Krumm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dadighat_M/0/1/0/all/0/1">Michelle Dadighat</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Goff_W/0/1/0/all/0/1">William Goff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Solomon_R/0/1/0/all/0/1">Rob Solomon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Padovan_S/0/1/0/all/0/1">Stefano Padovan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bolt_G/0/1/0/all/0/1">Greg Bolt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kardasis_E/0/1/0/all/0/1">Emmanuel Kardasis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Debackere_A/0/1/0/all/0/1">Andre Debackere</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thrush_J/0/1/0/all/0/1">Jeff Thrush</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stein_W/0/1/0/all/0/1">William Stein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Coulter_D/0/1/0/all/0/1">Daniel Coulter</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tsehmeystrenko_V/0/1/0/all/0/1">Valery Tsehmeystrenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gout_J/0/1/0/all/0/1">Jean-Francois Gout</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lewin_P/0/1/0/all/0/1">Pablo Lewin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Galdies_C/0/1/0/all/0/1">Charles Galdies</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fernandez_D/0/1/0/all/0/1">David Cejudo Fernandez</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Walker_G/0/1/0/all/0/1">Gary Walker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Boardman_J/0/1/0/all/0/1">James Boardman Jr.</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pellett_E/0/1/0/all/0/1">Emil Pellett</a>

The intermediate polar FO Aquarii experienced its first-reported
low-accretion states in 2016, 2017, and 2018. We establish that these low
states occurred shortly after the system’s white dwarf (WD) began spinning
down, after having spent a quarter-century spinning up. FO Aquarii is the only
intermediate polar whose period derivative has undergone a sign change, and it
has now done so twice. By combining our spin-pulse timings with previous data,
we determine that the WD’s spin period has varied quasi-sinusoidally since the
system’s discovery, and an extrapolation predicts that the white dwarf was
spinning down during newly discovered low states in photographic plates from
1964, 1965, and 1974. Thus, FO Aquarii’s low states appear to occur exclusively
during epochs of spindown. Additionally, our time-series photometry of the
2016-18 low states reveals that the mode of accretion is extremely sensitive to
the accretion rate; when the system is fainter than V~14.0, the accretion onto
the WD is largely stream-fed, but when it is brighter, it is almost exclusively
disk-fed. The system’s grazing eclipse remained detectable throughout all
observations, confirming the uninterrupted presence of a disk-like structure,
regardless of the accretion state. Our observations are consistent with
theoretical predictions that during the low states, the accretion disk
dissipates into a ring of diamagnetic blobs. Finally, a new XMM-Newton
observation from 2017 indicates that the system’s anomalously soft X-ray
spectrum and diminished X-ray luminosity in the wake of the 2016 low state
appear to be long-lasting changes compared to pre-2016 observations.

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