Browsing by Author "Ramos, Rodrigo Contreras"

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    HST proper motions on the far side of the Galactic bar-data
    (2023) Soto, Mario; Kuijken, Konrad; Rich, R. Michael; Clarkson, William, I; Castellon, Jose Luis Nilo; Fernandez-Trincado, Jose G.; Ramos, Rodrigo Contreras; Kunder, Andrea; Baravalle, Laura D.; Alonso, M. Victoria; Simion, Iulia T.; Johnson, Christian, I; Vieira, Katherine
    This is the third paper in a series that attempts to observe a clear signature of the Galactic bar/bulge using kinematic observations of the bulge stellar populations in low foreground extinction windows. We report on the detection of & SIM;100 000 new proper motions in four fields covering the far side of the Galactic bar/bulge, at negative longitudes. Our proper motions have been obtained using observations from the Advance Camera for Surveys (ACS), on board of the Hubble Space Telescope (HST), with a time-baseline of 8-9 years, which has produced accuracies better than 0.5 mas yr(-1) for a significant fraction of the stellar populations with F814W < 23 mag. Interestingly, as shown in previous works, the Hess diagrams show a strikingly similar proper motion distribution to fields closer to the Galactic center and consistent with an old stellar population. The observed kinematics point to a significant bulge rotation, which seems to predominate even in fields as far as l & SIME; -8 & DEG;, and is also reflected in the changes of the velocity ellipsoid in the l, b plane as a function of distance.
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    Variable stars in the VVV globular clusters
    (2017) Alonso-García, Javier; Catelan, Marcio; Ramos, Rodrigo Contreras; Dékány, István; Minniti, Dante
    The VVV survey observed some of the most crowded and most obscured regions in the inner MilkyWay during the last years. A significant sample of the less known globular clusters in our galaxy lie there. Combining the high-resolution, wide-field, nearinfrared capabilities of the survey camera, the use of 5 different filters, and multi-epoch observations, we are able to overcome many of the previous challenges that prevented a proper study of these objects. Particularly, the identification of the RR Lyrae stars in these globular clusters is proving to be a fundamental tool to establish accurately their distances and reddenings, and to infer information about the Oosterhoff dichotomy that Galactic globular clusters seem to follow.