4MOST Gaia RR Lyrae Survey (4GRoundS)

The 4GRoundS survey will measure the radial velocities and metallicities of southern RR Lyrae stars in Gaia Data Release 3. These stars have excellent photometric distances, allowing the exquisite Gaia proper motions to be converted into physically useful transverse velocities. Armed with the missing radial velocity, 4GRoundS will provide the community with a dataset that will enable studies of the orbital structure of the halo and outer disc, and allow realistic modelling of these components. It will also enable the identification of coherent dynamically cold streams. Together these analyses will map the mass of the Milky Way out to 100 kpc and test models of the dark sector.