On the erigone family and the z2 secular resonance

The Erigone family is a C-type group in the inner main belt. Its age has been estimated by several researchers to be less then 300 Myr, so it is a relatively young cluster. Yarko-YORP Monte Carlo methods to study the chronology of the Erigone family confirm results obtained by other groups. The Erigone family, however, is also characterized by its interaction with the z2 secular resonance. While less than 15 per cent of its members are currently in librating states of this resonance, the number of objects, members of the dynamical group, in resonant states is high enough to allow us to use the study of dynamics inside the z2 resonance to set constraints on the family age. Like the ν6 and z1 secular resonances, the z2 resonance is characterized by one stable equilibrium point at σ = 180° in the z2 resonance plane (σ, dσ/dt), where σ is the resonant angle of the z2 resonance. Diffusion in this plane occurs on time-scales of ≃ 12 Myr, which sets a lower limit on the Erigone family age. Finally, the minimum time needed to reach a steady-state population of z2 librators is about 90 Myr, which allows us to impose another, independent constraint on the group age.