The Dynamics and Stability of Circumbinary Orbits

We numerically investigate the dynamics of orbits in 3D circumbinary phase-space as a function of binary eccentricity and mass fraction. We find that inclined circumbinary orbits in the elliptically-restricted three-body problem display a nodal libration mechanism in the longitude of the ascending node and in the inclination to the plane of the binary. We (i) analyse and quantify the behaviour of these orbits with reference to analytical work performed by Farago & Laskar (2010) and (ii) investigate the stability of these orbits over time. This work is the first dynamically aware analysis of the stability of circumbinary orbits across both binary mass fraction and binary eccentricity. This work also has implications for exoplanetary astronomy in the existence and determination of stable orbits around binary systems.Comment: Monthly Notices of the Royal Astronomical Society. in pres

SS433's accretion disc, wind and jets: before, during and after a major flare

The Galactic microquasar SS433 occasionally exhibits a major flare when the intensity of its emission increases significantly and rapidly. We present an analysis of high-resolution, almost-nightly optical spectra obtained before, during and after a major flare, whose complex emission lines are deconstructed into single gaussians and demonstrate the different modes of mass loss in the SS433 system. During our monitoring, an initial period of quiescence was followed by increased activity which culminated in a radio flare. In the transition period the accretion disc of SS433 became visible in H-alpha and HeI emission lines and remained so until the observations were terminated; the line-of-sight velocity of the centre of the disc lines during this time behaved as though the binary orbit has significant eccentricity rather than being circular, consistent with three recent lines of evidence. After the accretion disc appeared its rotation speed increased steadily from 500 to 700 km/s. The launch speed of the jets first decreased then suddenly increased. At the same time as the jet launch speed increased, the wind from the accretion disc doubled in speed. Two days afterwards, the radio flux exhibited a flare. These data suggest that a massive ejection of material from the companion star loaded the accretion disc and the system responded with mass loss via different modes that together comprise the flare phenomena. We find that archival data reveal similar behaviour, in that when the measured jet launch speed exceeds 0.29c this is invariably simultaneous with, or a few days before, a radio flare. Thus we surmise that a major flare consists of the overloading of the accretion disc, resulting in the speeding up of the H-alpha rotation disc lines, followed by enhanced mass loss not just via its famous jets at higher-than-usual speeds but also directly from its accretion disc's wind.Comment: Accepted by MNRA

The precession of SS433's radio ruff on long timescales

Roughly perpendicular to SS433's famous precessing jets is an outflowing "ruff" of radio-emitting plasma, revealed by direct imaging on milli-arcsecond scales. Over the last decade, images of the ruff reveal that its orientation changes over time with respect to a fixed sky co-ordinate grid. For example, during two months of daily observations with the VLBA by Mioduszewski et al. (2004), a steady rotation through ~10 degrees is observed whilst the jet angle changes by ~20 degrees. The ruff reorientation is not coupled with the well-known precession of SS433's radio jets, as the ruff orientation varies across a range of 69 degrees whilst the jet angle varies across 40 degrees, and on greatly differing and non-commensurate timescales. It has been proposed that the ruff is fed by SS433's circumbinary disk, discovered by a sequence of optical spectroscopy by Blundell et al. (2008), and so we present the results of 3D numerical simulations of circumbinary orbits. These simulations show precession in the longitude of the ascending node of all inclined circumbinary orbits - an effect which would be manifested as the observed ruff reorientation. Matching the rate of ruff precession is possible if circumbinary components are sufficiently close to the binary system, but only if the binary mass fraction is close to equality and the binary eccentricity is non-zero.Comment: 4 pages, 5 figures, to be published in ApJ Le

Restorative justice : a crisis of identity? : tensions in restorative justice theory and in restorative responses to youth offending in England and New Zealand

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