The dependence of episodic accretion on eccentricity during the
  formation of binary stars
  Aims: Our goal is to investigate how the strength of episodic accretion
bursts depends on eccentricity. Methods: We investigate the binary trigger
hypothesis in longer-period (>20yr) binaries by carrying out three-dimensional
magnetohydrodynamical (MHD) simulations of the formation of low-mass binary
stars down to final separations of $\sim$10$\au$, including the effects of gas
turbulence and magnetic fields. We ran two simulations with an initial
turbulent gas core of one solar mass each and two different initial turbulent
Mach numbers, M = 0.1 and M=0.2, for 6500yr after protostar formation. Results:
We observe bursts of accretion at periastron during the early stages when the
eccentricity of the binary system is still high. We find that this correlation
between bursts of accretion and passing periastron breaks down at later stages
because of the gradual circularisation of the orbits. For eccentricities
greater than e=0.2, we observe episodic accretion triggered near periastron.
However, we do not find any strong correlation between the strength of episodic
accretion and eccentricity. The strength of accretion is defined as the ratio
of the burst accretion rate to the quiescent accretion rate.We determine that
accretion events are likely triggered by torques between the rotation of the
circumstellar disc and the approaching binary stars. We compare our results
with observational data of episodic accretion in short-period binaries and find
good agreement between our simulations and the observations. Conclusions: We
conclude that episodic accretion is a universal mechanism operating in
eccentric young binary-star systems, independent of separation, and it should
be observable in long-period binaries as well as in short-period binaries.
Nevertheless, the strength depends on the torques and hence the separation at
periastron.
