Detailed study of the Milky Way globular cluster Laevens 3. (arXiv:1909.08622v1 [astro-ph.GA])

Detailed study of the Milky Way globular cluster Laevens 3. (arXiv:1909.08622v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Longeard_N/0/1/0/all/0/1">Nicolas Longeard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martin_N/0/1/0/all/0/1">Nicolas Martin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ibata_R/0/1/0/all/0/1">Rodrigo A. Ibata</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Collins_M/0/1/0/all/0/1">Michelle L.M. Collins</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laevens_B/0/1/0/all/0/1">Benjamin P.M. Laevens</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bell_E/0/1/0/all/0/1">Eric Bell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mackey_D/0/1/0/all/0/1">Dougal Mackey</a>

We present a photometric and spectroscopic study of the Milky Way satellite
Laevens 3. Using MegaCam/CFHT 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 (Mv = -2.8+0.2-0.3 mag) and
compact (r = 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 ( = -70.2+-0.5 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 which strengthens our conclusion that Laevens 3
is a globular cluster.

We present a photometric and spectroscopic study of the Milky Way satellite
Laevens 3. Using MegaCam/CFHT 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 (Mv = -2.8+0.2-0.3 mag) and
compact (r = 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 (<vr> = -70.2+-0.5 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 which strengthens our conclusion that Laevens 3
is a globular cluster.

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