Oxford University Press (OUP), Monthly Notices of the Royal Astronomical Society, 2(490), p. 1498-1508, 2019
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ABSTRACT We present a photometric and spectroscopic study of the Milky Way satellite Laevens 3. Using MegaCam/Canada–France–Hawaii Telescope $g$ and $i$ photometry and Keck II/DEIMOS multi-object spectroscopy, we refine the structural and stellar properties of the system. The Laevens 3 colour–magnitude diagram shows that it is quite metal-poor, old ($13.0 ± 1.0$ Gyr), and at a distance of $61.4 ± 1.0$ kpc, partly based on two RR Lyrae stars. The system is faint ($M_V = -2.8^{+0.2}_{-0.3}$ mag) and compact ($r_h = 11.4 ± 1.0$ pc). From the spectroscopy, we constrain the systemic metallicity (${\rm [Fe/H]}_\mathrm{spectro} = -1.8 ± 0.1$ dex) but the metallicity and velocity dispersions are both unresolved. Using Gaia DR2, we infer a mean proper motion of $(μ _α ^*,μ _δ)=(0.51 ± 0.28,-0.83 ± 0.27)$ mas yr−1, which, combined with the system’s radial velocity ($〈 v_r〉 = -70.2 ± 0.5 {\rm \, km \,\, s^{-1}}$), translates into a halo orbit with a pericenter and apocenter of $40.7 ^{+5.6}_{-14.7}$ and $85.6^{+17.2}_{-5.9}$ kpc, respectively. Overall, Laevens 3 shares the typical properties of the Milky Way’s outer halo globular clusters. Furthermore, we find that this system shows signs of mass segregation that strengthens our conclusion that Laevens 3 is a globular cluster.