Precession and accretion in circumbinary discs: the case of HD 104237

Abstract

We present the results of smoothed particle hydrodynamics (SPH) simulations of the disc around the young, eccentric stellar binary HD 104237. We find that the binary clears out a large cavity in the disc, driving a significant eccentricity at the cavity edge. This then precesses around the binary at a rate of˙ = 0.48 • T −1 b , which for HD 104237 corresponds to a precession period of 40 years. We find that the accretion pattern into the cavity and onto the binary changes with this precession, resulting in a periodic accretion variability driven purely by the physical parameters of the binary and its orbit. For each star we find that this results in order of magnitude changes in the accretion rate. We also find that the accretion variability allows the primary to accrete gas at a higher rate than the secondary for approximately half of each precession period. Using a large number of 3-body integrations of test particles orbiting different binaries, we find good agreement between the precession rate of a test particle and our SPH disc precession. These rates also agree very well with the precession rates predicted by the analytic theory of Leung & Lee (2013), showing that their prescription can be accurately used to predict long-term accretion variability timescales for eccentric binaries accreting from a disc. We discuss the implications of our result, and suggest that this process provides a viable way of preserving unequal mass ratios in accreting eccentric binaries in both the stellar and supermassive black hole regimes.

Circumbinary discs: Numerical and physical behaviour

“…Pierens & Nelson 2013;Kley & Haghighipour 2014;Dunhill et al 2015). The recent simulations of circumbinary disk by Pierens & Nelson (2013), Kley & Haghighipour (2014) and Lines et al (2015) used grid-based numerical methods on a polar grid with an inner hole.…”

A transition in circumbinary accretion discs at a binary mass ratio of 1:25

“…This is illustrated by the surface density contours in the bottom panels of Figure 9. A lopsided cavity has been observed in previous studies which have used different numerical codes and physical assumptions (MacFadyen & Milosavljević 2008;Shi et al 2012;Noble et al 2012;D'Orazio et al 2013;Farris et al 2014Farris et al , 2015aDunhill et al 2015;Shi & Krolik 2015). A complete description of the growth of lopsided cavities, especially in the symmetric equal-mass binary case, does not yet exist.…”

“…Additionally, interaction of the binary and disc can lead to periodic accretion (Hayasaki et al 2007;MacFadyen & Milosavljević 2008;Cuadra et al 2009;Roedig et al 2011;Noble et al 2012;Shi et al 2012;Roedig et al 2012;D'Orazio et al 2013;Farris et al 2014;Dunhill et al 2015;Shi & Krolik 2015) which can aid in identifying MBHB candidates in electromagnetic (EM) surveys (Haiman et al 2009). As has been recently been made clear by the discovery of multiple MBHB candidates in EM time-domain surveys (Graham et al 2015b,a;Liu et al 2015), the interpretation of variability in EM surveys will rely heavily on our knowledge of how accretion variability depends on system parameters such as the binary mass ratio (see e.g.…”

Rotationally Driven Fragmentation in the Formation of the Binary Protostellar System L1551 Irs 5

“…For eccentric coplanar systems, Artymowicz & Lubow (1996) find that accretion is stronger onto the circumstellar disk of the secondary component. A recent study by Dunhill et al (2015), however, paints a more complicated picture for accretion in eccentric coplanar systems. They performed hybrid smoothed-particle hydrodynamics (SPH)/Nbody simulations of a binary system with a moderately high eccentricity (e=0.6) and a moderately small mass ratio (q=0.64) accreting from its circumbinary disk.…”