Detailed study of the Milky Way globular cluster Laevens 3
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2019
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Abstract
We present a photometric and spectroscopic study of the Milky Way satellite Laevens 3. UsingMegaCam/Canada-France-Hawaii Telescope g and i photometry andKeck 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 +/- 1.0Gyr), 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(-0.3)(+0.2) mag) and compact (r(h) = 11.4 +/- 1.0 pc). From the spectroscopy, we constrain the systemic metallicity ([Fe/H](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 (mu(alpha)*, mu(delta)) = (0.51 +/- 0.28,-0.83 +/- 0.27) mas yr(-1), which, combined with the system's radial velocity (< v(r)> = -70.2 +/- 0.5km s(-1)), translates into a halo orbit with a pericenter and apocenter of 40.7(-14.7)(+5.6) and 85.6(-5.9)(+17.2) 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.
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Local Group