Modelling the M68 stellar stream with realistic mass loss and frequency distributions in angle-action coordinates

Abstract

We develop a new method for simulating stellar streams generated by globular clusters using angle-action coordinates. This method reproduces the variable mass-loss and variable frequency of the stripped stars caused by the changing tidal forces acting on the cluster as it moves along an eccentric orbit. The model incorporates realistic distributions for the stripping angle and frequency of the stream stars both along and perpendicular to the stream. The stream is simulated by generating random samples of stripped stars and integrating them forward in time in angle-frequency space. Once the free parameters are calibrated, this method can be used to simulate the internal structure of stellar streams more quickly than N-body simulations, while achieving a similar level of accuracy. We use this model to study the surface density of the stellar stream produced by the globular cluster M68 (NGC 4590). We select $291$ stars from the Gaia-DR3 catalogue along the observable section that are likely to be members of the stream. We find that the width of the stream is too large to be explained by stars stripped from the cluster alone. We simulate the stream using the present method and include the Gaia selection function and observational errors, and the process of separating the stream stars from the foreground. By comparing these results with the observed data, we estimate the age of the stream, or equivalently the cluster accretion time, to be $3.04_{-0.29}^{+5.63}$ Gyr, and the mass-loss of the cluster to be $0.496 \pm 0.030$ M$_{\odot}$ Myr$^{-1}$ arm$^{-1}$.