Constraining the Milky Way halo potential with the GD-1 stellar stream

Abstract We use ESA/Gaia astrometry together with SEGUE and LAMOST measurements of the GD-1 stellar stream to explore the improvement on the Galactic gravitational potential that these new data provide. Assuming a realistic universal model for the dark matter halo together with reasonable models of the baryonic components, we find that the orbital solutions for GD-1 require the circular velocity at the Solar radius to be V ₂₈ₑ₂ (R_) =244 4 \, km\, s^{-1}, and also that the density flattening of the dark halo is q =0. 82^+0. 25-₀. ₁₃. The corresponding Galactic mass within 20 \, kpc was estimated to be M ₌ₖ (20 \, kpc) =2. 5 0. 2 10^11 \, M_. Moreover, Gaia’s excellent proper motions also allowed us to constrain the velocity dispersion of the GD-1 stream in the direction tangential to the line of sight to be 2. 30 \, km\, s^{-1} (95 per cent confidence limit), confirming the extremely cold dynamical nature of this system.