Browsing by Author "Ibata, Rodrigo A."

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    Detailed study of the Milky Way globular cluster Laevens 3
    (2019) Longeard, Nicolas; Martin, Nicolas; Ibata, Rodrigo A.; Collins, Michelle L. M.; Laevens, Benjamin P. M.; Bell, Eric; Mackey, Dougal
    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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    Pristine dwarf galaxy survey - I. A detailed photometric and spectroscopic study of the very metal-poor Draco II satellite
    (2018) Longeard, Nicolas; Martin, Nicolas; Starkenburg, Else; Ibata, Rodrigo A.; Collins, Michelle L. M.; Geha, Marla; Laevens, Benjamin P. M.; Rich, R. Michael; Aguado, David S.; Arentsen, Anke; Carlberg, Raymond G.; Cote, Patrick; Hill, Vanessa; Jablonka, Pascale; Gonzalez Hernandez, Jonay I.; Navarro, Julio F.; Sanchez-Janssen, Ruben; Tolstoy, Eline; Venn, Kim A.; Youakim, Kris
    We present a detailed study of the faint Milky Way satellite Draco II (Dra II) from deep CFHT/MegaCam broad-band g and i photometry and narrow-band metallicity-sensitive CaliK observations, along with follow-up Keck II/DEIMOS multi-object spectroscopy. Forward modelling of the deep photometry allows us to refine the structural and photometric properties of Dra II: the distribution of stars in colour-magnitude space implies Dra II is old (13.5 +/- 0.5 Gyr), very metal-poor, very faint (L-v = 180(-72)(+124) L-circle dot), and at a distance d = 21.5 +/- 0.4 kpc. The narrow-band, metallicity-sensitive Cal-IK Pristine photometry confirms this very low metallicity ([Fe/H] = -2.7 +/- 0.1 dex). Even though our study benefits from a doubling of the spectroscopic sample size compared to previous investigations, the velocity dispersion of the system is still only marginally resolved (sigma(vr) < 5.9 km s(-1) at the 95 per cent confidence level) and confirms that Dra II is a dynamically cold stellar system with a large recessional velocity (< v(r)> = -342.5(-1.2)(+1.1)km s(-)1). We further show that the spectroscopically confirmed members of Dra II have a mean proper motion of (mu(alpha)*, mu(delta)) = (1.26 +/- 0.27, 0.94 +/- 0.28) mas/yr in the Gaia DR2 data, which translates to an orbit with a pericentre and an apocentre of 21.3(-1.0)(+0.7) and 153.8(-34.7)(+56.7) kpc, respectively. Taken altogether, these properties favour the scenario of Dra II being a potentially disrupting dwarf galaxy. The low-significance extra-tidal features we map around the satellite tentatively support this scenario.