Examinando por Autor "Rejkuba, Marina"
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Ítem Astrometry in crowded fields towards the Galactic bulge(EDP Sciences, 2023-09) Luna, Alonso; Marchetti, Tommaso; Rejkuba, Marina; Minniti, DanteContext. The astrometry towards the Galactic bulge is hampered by high stellar crowding and patchy extinction. This effect is particularly severe for optical surveys such as the European Space Agency satellite Gala. Aims. In this study, we assess the consistency of proper motion measurements between optical (Gaia DR3) and near-infrared (VIRAC2) catalogues in comparison with proper motions measured with the Hubble Space Telescope (HST) observations in several crowded fields towards the Galactic bulge and in Galactic globular clusters. Methods. Assuming that the proper motion measurements are well characterised, the uncertainty-normalised proper motion differences between pairs of catalogues are expected to follow a normal distribution. A deviation from a normal distribution defines the inflation factor r. By multiplying the proper motion uncertainties with the appropriate inflation factor values, the Gaia (VIRAC2) proper motion measurements are brought into a 1ÏÃ Â agreement with the HST proper motions. Results. The inflation factor (r) depends on stellar surface density. For the brightest stars in our sample (G < 18), the dependence on G-band magnitude is strong, corresponding to the most precise Gaia DR3 proper motions. We used the number of observed Gaia DR3 sources as a proxy for the stellar surface density. Assuming that the HST proper motion measurements are well determined and free from systematic errors, we find that Gaia DR3 proper motion uncertainties are better characterised, having r < 1.5 in fields with a stellar number density with fewer than 200 Gaia DR3 sources per arcmin2, and are underestimated by up to a factor of 4 in fields with stellar densities higher than 300 sources per arcmin2. For the most crowded fields in VIRAC2, the proper motion uncertainties are underestimated by a factor of 1.1 up to 1.5, with a dependence on J-band magnitude. In all fields, the brighter sources have the higher r value. At the faint end (G > 19), the inflation factor is close to 1, meaning that the proper motions already fully agree with the HST measurements within 1. Conclusions. In the crowded fields common to both catalogues, VIRAC2 proper motions agree with HST proper motions and do not need an inflation factor for their uncertainties. Because of the depth and completeness of VIRAC2 in these fields, it is an ideal complement to Gaia DR3 for proper motion studies towards the Galactic bulge. © 2023 EDP Sciences. All rights reserved.Ítem FSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars(Institute of Physics Publishing, 2017-03) Minniti, Dante; Palma, Tali; Dékány, Istvan; Hempel, Maren; Rejkuba, Marina; Pullen, Joyce; Alonso-García, Javier; Barbá, Rodolfo; Barbuy, Beatriz; Bica, Eduardo; Bonatto, Charles; Borissova, Jura; Catelan, Marcio; Carballo-Bello, Julio A.; Chene, Andre Nicolas; Clariá, Juan José; Cohen, Roger E.; Contreras Ramos, Rodrigo; Dias, Bruno; Emerson, Jim; Froebrich, Dirk; Buckner, Anne S. M.; Geisler, Douglas; Gonzalez, Oscar A.; Gran, Felipe; Hagdu, Gergely; Irwin, Mike; Ivanov, Valentin D.; Kurtev, Radostin; Lucas, Philip W.; Majaess, Daniel; Mauro, Francesco; Moni-Bidin, Christian; Navarrete, Camila; Alegría, Sebastian Ramírez; Saito, Roberto K.; Valenti, Elena; Zoccali, ManuelaWe use deep multi-epoch near-IR images of the VISTA Variables in the Vía Láctea (VVV) Survey to search for RR Lyrae stars toward the Southern Galactic plane. Here, we report the discovery of a group of RR Lyrae stars close together in VVV tile d025. Inspection of the VVV images and PSF photometry reveals that most of these stars are likely to belong to a globular cluster that matches the position of the previously known star cluster FSR 1716. The stellar density map of the field yields a >100σ detection for this candidate globular cluster that is centered at equatorial coordinates R.A.J2000 = 16:10:30.0, decl.J2000 = -53:44:56 and galactic coordinates l = 329.77812, b = -1.59227. The color-magnitude diagram of this object reveals a well-populated red giant branch, with a prominent red clump at K s = 13.35 ±0.05, and J - K s = 1.30 ±0.05. We present the cluster RR Lyrae positions, magnitudes, colors, periods, and amplitudes. The presence of RR Lyrae indicates an old globular cluster, with an age >10 Gyr. We classify this object as an Oosterhoff type I globular cluster, based on the mean period of its RR Lyrae type ab, days, and argue that this is a relatively metal-poor cluster with [Fe/H] = -1.5 ±0.4 dex. The mean extinction and reddening for this cluster are and E(J - K s) = 0.72 ±0.02 mag, respectively, as measured from the RR Lyrae colors and the near-IR color-magnitude diagram. We also measure the cluster distance using the RR Lyrae type ab stars. The cluster mean distance modulus is (m - M)0 = 14.38 ±0.03 mag, implying a distance D = 7.5 ±0.2 kpc and a Galactocentric distance R G = 4.3 kpc. © 2017. The American Astronomical Society. All rights reserved.Ítem Interstellar extinction curve variations towards the inner Milky Way: A challenge to observational cosmology(Oxford University Press, 2016-03) Nataf, David M.; Gonzalez, Oscar A.; Casagrande, Luca; Zasowski, Gail; Wegg, Christopher; Wolf, Christian; Kunder, Andrea; Alonso-Garcia, Javier; Minniti, Dante; Rejkuba, Marina; Saito, Roberto K.; Valenti, Elena; Zoccali, Manuela; Poleski, Radosław; Pietrzyński, Grzegorz; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Udalski, Andrzej; Ulaczyk, Krzyszto; Wyrzykowski, ŁukaszWe investigate interstellar extinction curve variations towards ∼4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent mea surements towards ∼2000 sightlines of AI, E(V − I), E(I − J) and E(J − Ks), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI/E(V − I), E(I − J)/E(V − I) and E(J − Ks)/E(V − I) are large (exceeding 20 per cent), signifi cant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV), which we confirm with a principal component analysis. We derive a median value of AV/AKs = 13.44, which is ∼60 per cent higher than the ‘standard’ value. We show that the Wesenheit magnitude WI = I − 1.61(I − J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ∼100 per cent and lack sensitivity to extinction curve variations.Ítem Search for hypervelocity stras in the central regions of the galaxy(Universidad Andrés Bello, 2023) Ruiz Fernández, Alonso Luna; Minniti, D.; Rejkuba, Marina; Marchetti, Tommaso; Alonso García, Javier; Leigh, Nathan; Facultad de Ciencias ExactasIn this thesis, I propose a new approach to search for hypervelocity stars in the inner part of our Galaxy. Hypervelocity stars are moving at velocities around 1000 km s−1 , acquiring such velocity after an interaction with the supermassive black hole at the centre of the Milky Way: Sgr A*. Hence, these stars inform us about i) dynamical stellar interactions with Sgr A*, ii) phenomena in regions with high stellar density, iii) the stellar content in the inner part of the Galaxy, and iv) the presence of massive objects, such as intermediate and stellar-mass black holes. Hypervelocity stars are extremely rare, to identify them it was necessary to characterise the proper motions of the stars in the used catalogues: Gaia , VVV and VIRAC2, which contain hundreds of millions of sources. I explore also different approaches to identify and validate the reliable data in such catalogues, that result in being able to identify the unique objects in these catalogues, in this case, hypervelocity stars. The results of this work are the characterisation of the astrometric data of Gaia DR3 and VIRAC2 with respect to data from the Hubble Space Telescope (HST) in observations towards the Galactic bulge. On one hand, the uncertainties in the proper motions of Gaia DR3 are underestimated with respect to the HST proper motions, thus the need for an inflation factor to bring them into a 1σ consistency. On the other hand, VIRAC2 proper motions are in agreement with HST proper motions. For this reason, I used VIRAC2 proper motions to search for hypervelocity stars. With the developed method, I identified 139 candidate hypervelocity stars in the inner 60 sqdeg. around the Galactic centre. These stars appear to be ejected after an interaction with Sgr A *. Besides that, we identified more than 1000 high-velocity stars (> 600 km s−1 ), probably produced in the Galactic disc, although their origin is uncertain.Ítem The structure behind the Galactic bar traced by red clump stars in the VVV survey(Oxford University Press, 2018-11) Gonzalez, Oscar A.; Minniti, Dante; Valenti, Elena; Alonso-García, Javier; Debattista, Victor P.; Zoccali, Manuela; Rejkuba, Marina; Dias, Bruno; Surot, Francisco; Hempel, Maren; Saito, Roberto K.Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the Vía Láctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes - 10° < l < 10° and latitudes -1.5° < b < 1.5°. We use these dereddened catalogues to construct the Ks luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulge red-giant branch bump alone, as previously interpreted. Instead, this fainter clump corresponds largely to the over-density of red clump stars tracing the spiral arm structure behind the Galactic bar. This result suggests that studies aiming to characterize the bulge red-giant branch bump should avoid low galactic latitudes (|b| < 2°), where the background red clump population contributes significant contamination. It furthermore highlights the need to include this structural component in future modelling of the Galactic bar. © 2018 The Author(s).