Examinando por Autor "Belokurov, Vasily"
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Ítem Kinematics and chemistry of recently discovered reticulum 2 and horologium 1 dwarf galaxies(Institute of Physics Publishing, 2015-09) Koposov, Sergey E.; Casey, Andrew R.; Belokurov, Vasily; Lewis, James R.; Gilmore, Gerard; Worley, Clare; Hourihane, Anna; Randich, S.; Bensby, T.; Bragaglia, A.; Bergemann, M.; Carraro, G.; Costado, M.T.; Flaccomio, E.; Francois, P.; Heiter, U.; Hill, V.; Jofre, P.; Lando, C.; Lanzafame, A.C.; Laverny, P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Mikolaitis, Š.; Ryde, N.We report on VLT/GIRAFFE spectra of stars in two recently discovered ultra-faint satellites, Reticulum 2 and Horologium 1, obtained as part of the Gaia-ESO Survey. We identify 18 members in Reticulum 2 and five in Horologium 1. We find Reticulum 2 to have a velocity dispersion of , implying a mass-to-light ratio (M/L) of ∼500. The mean metallicity of Reticulum 2 is , with an intrinsic dispersion of ∼0.3 dex and α-enhancement of ∼0.4 dex. We conclude that Reticulum 2 is a dwarf galaxy. We also report on the serendipitous discovery of four stars in a previously unknown stellar substructure near Reticulum 2 with and , far from the systemic velocity of Reticulum 2. For Horologium 1 we infer a velocity dispersion of and a M/L ratio of ∼600, leading us to conclude that Horologium 1 is also a dwarf galaxy. Horologium 1 is slightly more metal-poor than Reticulum 2 () and is similarly α-enhanced: with a significant spread of metallicities of 0.17 dex. The line-of-sight velocity of Reticulum 2 is offset by 100 km s-1 from the prediction of the orbital velocity of the Large Magellanic Cloud (LMC), thus making its association with the Cloud uncertain. However, at the location of Horologium 1, both the backward-integrated orbit of the LMC and its halo are predicted to have radial velocities similar to that of the dwarf. Therefore, it is possible that Horologium 1 is or once was a member of the Magellanic family. © 2015. The American Astronomical Society. All rights reserved..Ítem Variable star classification across the Galactic bulge and disc with the VISTA Variables in the Vía Láctea survey(2022-01) Molnar, Thomas A; L. Sanders, Jason; Leigh C, Smith,; Belokurov, Vasily; Lucas, Philip; Minniti, DanteWe present VIVACE, the VIrac VAriable Classification Ensemble, a catalogue of variable stars extracted from an automated classification pipeline for the Vista Variables in the Vía Láctea (VVV) infrared survey of the Galactic bar/bulge and southern disc. Our procedure utilizes a two-stage hierarchical classifier to first isolate likely variable sources using simple variability summary statistics and training sets of non-variable sources from the Gaia early third data release, and then classify candidate variables using more detailed light-curve statistics and training labels primarily from OGLE and VSX. The methodology is applied to point-spread-function photometry for 490 million light curves from the VIRAC v2 astrometric and photometric catalogue resulting in a catalogue of 1.4 million likely variable stars, of which 39 000 are high-confidence (classification probability >0.9) RR Lyrae ab stars, 8000 RR Lyrae c/d stars, 187, 000 detached/semi-detached eclipsing binaries, 18, 000 contact eclipsing binaries, 1400 classical Cepheid variables and 2200 Type II Cepheid variables. Comparison with OGLE-4 suggests a completeness of around $90, $ for RRab and $lesssim 60, $ for RRc/d, and a misclassification rate for known RR Lyrae stars of around $1, $ for the high confidence sample. We close with two science demonstrations of our new VIVACE catalogue: first, a brief investigation of the spatial and kinematic properties of the RR Lyrae stars within the disc/bulge, demonstrating the spatial elongation of bar-bulge RR Lyrae stars is in the same sense as the more metal-rich red giant population whilst having a slower rotation rate of $sim !40, {km, s}{-1}{kpc}{-1}$ and secondly, an investigation of the GaiaEDR3 parallax zero-point using contact eclipsing binaries across the Galactic disc plane and bulge. © 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.