On the ephemeris of the eclipsing polar HU Aquarii. II: New eclipse epochs obtained 2014–2018

Abstract

The magnetic cataclysmic variable HU Aquarii displayed pronounced modulations of its eclipse timing. In recent years, these have been intensively modeled and discussed in the framework of planets orbiting the binary or the Applegate effect. No scenario yielded a unique and satisfactory interpretation of the data. Here, we present 26 new eclipse epochs obtained between 2014 and 2018. The steep and continuous decrease of the orbital period observed in the time interval 2010-2013 has slowed down sometimes before mid 2016. The new slope in the (O − C)-diagram of eclipse arrival times will further constrain physical models of its complex shape.

Nova-produced Common Envelope: Source of the Non-solar Abundances and an Additional Frictional Angular Momentum Loss in Cataclysmic Variables

“…The CV type, period, mass ratio, and secondary are from Ritter & Kolb (2003)'s catalogue, which was last updated on Dec 31, 2015. Orbital periods for V603 Cas, J1544+2553, RW Sex, UU Aql, V380 Oph, QZ Ser, SU UMa, QZ Vir and EI Psc are from Thoretensen et al (2017), for TW Vir from Dai et al (2017), for HU Aqr from Schwope & Thinius (2018) and for AR UMa from Bai et al (2016). The latter also found that an AlI absorption line doublet in the visual varied.…”

An Eccentric Planet Orbiting the Polar V808 Aurigae

“…Eclipse timings from the polar HU Aqr initially suggested multiple planet candidates orbiting the close binary (Qian et al 2011). However, extending the observation baseline revealed timing variations that could not be explained solely by a multiple planet hypothesis (Schwope & Thinius 2014, 2018. The source of this timing variability remains uncertain.…”

“…There have been attempts to explain orbital variations seen in eclipsing binaries through the Applegate mechanism (Applegate 1992;Lanza 2006), where a magnetically active late-type companion redistributes its angular momentum via changes in its subsurface magnetic field. Estimates of the connection between changes in the quadrupole moment of the secondary and the resulting variation in the orbital period of the binary suggest that the Applegate mechanism is near the limit of explaining the amplitude of the O − C variations in HU Aqr (Schwope & Thinius 2018). However, a combination of planets and the Applegate mechanism could work for HU Aqr (Bours et al 2014).…”

“…While the eclipse timing variations in V808 Aur are well modeled by the passage of a planet-sized body, there may be other explanations for the observed O − C changes. Eclipse timings of the polar HU Aqr have shown complex changes that are difficult to model with orbits of even multiple planets (Schwope & Thinius 2018). There have been attempts to explain orbital variations seen in eclipsing binaries through the Applegate mechanism (Applegate 1992;Lanza 2006), where a magnetically active late-type companion redistributes its angular momentum via changes in its subsurface magnetic field.…”

“…Large-amplitude eclipse timing variations have been observed in at least three other eclipsing polars: HU Aqr (Qian et al 2011), DP Leo (Qian et al 2010Beuermann et al 2011), and UZ For (Potter et al 2011). For each of these systems, a circumbinary planetary system has been proposed as one possible explanation for the peculiar eclipse timings, and a commonality has been that these planetary models struggle to predict with high accuracy future times of mideclipse (HU Aqr: Schwope & Thinius 2014, 2018DP Leo: Boyd 2017; and UZ For: Khangale et al 2019). This suggests that a combination of factors, including a planetary system, the Applegate mechanism, and/or an unknown mechanism of angular momentum loss, collectively influence the eclipse timings (Schwope & Thinius 2018).…”