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Cohen R.E.,University of Concepción | Hempel M.,University of Santiago de Chile | Mauro F.,Instituto Milenio Of Astrofisica | Geisler D.,University of Concepción | And 3 more authors.
Astronomical Journal | Year: 2015

We present wide field near-infrared (near-IR) photometry of 12 Galactic globular clusters, typically extending from the tip of the cluster red giant branch (RGB) to the main sequence turnoff. Using recent homogenous values of cluster distance, reddening and metallicity, the resulting photometry is directly compared to the predictions of several recent libraries of stellar evolutionary models. Of the sets of models investigated, Dartmouth and Victoria- Regina models best reproduce the observed RGB morphology, albeit with offsets in J - KS color which vary in their significance in light of all sources of observational uncertainty. Therefore, we also present newly recalibrated relations between near-IR photometric indices describing the upper RGB versus cluster iron abundance as well as global metallicity. The influence of enhancements in alpha elements and helium are analyzed, and we find that the former affect the morphology of the upper RGB in accord with model predictions. Meanwhile, the empirical relations we derive are in good agreement with previous results, and minor discrepancies can likely be attributed to differences in the assumed cluster distances and reddenings. In addition, we present measurements of the horizontal branch (HB) and RGB bump magnitudes, finding a non-negligible dependence of the near-IR HB magnitude on cluster metallicity. Lastly, we discuss the influence of assumed cluster distances, reddenings and metallicities on our results, finding that our empirical relations are generally insensitive to these factors to within their uncertainties. © 2015 The American Astronomical Society. All rights reserved.

Dekany I.,Instituto Milenio Of Astrofisica | Dekany I.,University of Santiago de Chile | Minniti D.,Instituto Milenio Of Astrofisica | Minniti D.,Andrés Bello University | And 15 more authors.
Astrophysical Journal Letters | Year: 2015

Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy's evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years. © 2015. The American Astronomical Society. All rights reserved.

Gonzalez O.A.,European Southern Observatory | Gonzalez O.A.,University of Edinburgh | Zoccali M.,University of Santiago de Chile | Zoccali M.,Instituto Milenio Of Astrofisica | And 7 more authors.
Astronomy and Astrophysics | Year: 2015

The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios. © 2015 ESO.

Minniti D.,Instituto Milenio Of Astrofisica | Minniti D.,Andrés Bello University | Minniti D.,Vatican Observatory | Ramos R.C.,Instituto Milenio Of Astrofisica | And 9 more authors.
Astrophysical Journal Letters | Year: 2016

Galactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RR Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way. © 2016. The American Astronomical Society. All rights reserved..

Jurcsik J.,Hungarian Academy of Sciences | Smitola P.,Hungarian Academy of Sciences | Hajdu G.,University of Santiago de Chile | Hajdu G.,Instituto Milenio Of Astrofisica | And 16 more authors.
Astrophysical Journal, Supplement Series | Year: 2015

The overtone and multi-mode RR Lyrae stars in the globular cluster M3 are studied using a 200 day long, B, V, and IC time-series photometry obtained in 2012. 70% of the 52 overtone variables observed show some kind of multi-periodicity (with additional frequency at f0.61 = f1O 0.61 frequency ratio, Blazhko effect, double/multi-mode pulsation, and period doubling). A signal at the 0.587 frequency ratio to the fundamental-mode frequency is detected in the double-mode star, V13, which may be identified as the second radial overtone mode. If this mode identification is correct, than V13 is the first RR Lyrae star showing triple-mode pulsation of the first three radial modes. Either the Blazhko effect or the f0.61 frequency (or both of these phenomena) appears in seven doublemode stars. The P1O PF period ratio of RRd stars showing the Blazhko effect are anomalous. A displacement of the main frequency component at the fundamental mode with the value of modulation frequency (or its half), is detected in three Blazhko RRd stars that are parallel with the appearance of the overtone-mode pulsation. The f0.61 frequency appears in RRc stars that lie at the blue side of the double-mode region and in RRd stars, raising the suspicion that its occurrence may be connected to double-mode pulsation. The changes of the Blazhko and doublemode properties of the stars are also reviewed using the recent and archive photometric data. © 2015. The American Astronomical Society. All rights reserved.

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