Browsing by Author "Navarrete, Camila"

Now showing 1 - 4 of 4
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    Elevated r-process Enrichment in Gaia Sausage and Sequoia*
    (2021) Aguado, David S.; Belokurov, Vasily; Myeong, G. C.; Evans, N. Wyn; Kobayashi, Chiaki; Sbordone, Luca; Chaname, Julio; Navarrete, Camila; Koposov, Sergey E.
    The Gaia Sausage (GS) and the Sequoia represent the major accretion events that formed the stellar halo of the Milky Way. A detailed chemical study of these main building blocks provides a pristine view of the early steps of the Galaxy's assembly. We present the results of the analysis of the UVES high-resolution spectroscopic observations at the 8.2 m VLT of nine Sausage/Sequoia members selected kinematically using Gaia DR2. We season this set of measurements with archival data from Nissen & Schuster and GALAH DR3 (2020). Here, we focus on the neutron-capture process by analyzing Sr, Y, Ba, and Eu behavior. We detect clear enhancement in Eu abundance ([Eu/Fe] similar to 0.6-0.7) indicative of large prevalence of the r-process in the stellar n-capture makeup. We are also able to trace the evolution of the heavy element production across a wide range of metallicity. The barium to europium changes from a tight, flat sequence with [Ba/Eu] = -0.7 reflecting dominant contribution from exploding massive stars, to a clear upturn at higher iron abundances, betraying the onset of contamination from asymptotic giant branch (AGB) ejecta. Additionally, we discover two clear sequences in the [Fe/H]-[Ba/Fe] plane likely caused by distinct levels of s-process pollution and mixing within the GS progenitor.
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    RR Lyrae stars as tracers of halo substructures
    (2017) Duffau, Sonia; Vivas, A. Katherina; Navarrete, Camila; Carballo-Bello, Julio; Hajdu, Gergel; Catelan, Marcio
    Three RR Lyrae overdensity candidates in the southern sky have been studied using low resolution spectra obtained with the Goodman spectrograph at SOAR. We search for unidentified velocity peaks indicative of the possible presence of streams within the overdensities. Our results suggest that all three overdensities present an excess of radial velocity signal at high mean radial velocities which cannot be explained as a contribution from any known Galactic component....
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    The S2 stream: the shreds of a primitive dwarf galaxy
    (2021) Aguado, David S.; Myeong, G. C.; Belokurov, Vasily; Evans, N. Wyn; Koposov, Sergey E.; Allende Prieto, Carlos; Lanfranchi, Gustavo A.; Matteucci, Francesca; Shetrone, Matthew; Sbordone, Luca; Navarrete, Camila; Gonzalez Hernandez, Jonay, I; Chaname, Julio; Peralta de Arriba, Luis; Yuan, Zhen
    The S2 stream is a kinematically cold stream that is plunging downwards through the Galactic disc. It may be part of a hotter and more diffuse structure called the Helmi stream. We present a multi-instrument chemical analysis of the stars in the metal-poor S2 stream using both high- and low-resolution spectroscopy, complemented with a re-analysis of the archival data to give a total sample of 62 S2 members. Our high-resolution program provides alpha-elements (C, Mg, Si, Ca, and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture process elements (Sr, Ba), and other elements such as Li, Na, Al, and Sc for a subsample of S2 objects. We report coherent abundance patterns over a large metallicity spread (similar to 1 dex) confirming that the S2 stream was produced by a disrupted dwarf galaxy. The combination of S2's alpha-elements displays a mildly decreasing trend with increasing metallicity, which can be tentatively interpreted as a 'knee' at [Fe/H] < -2. At the low-metallicity end, the n-capture elements in S2 may be dominated by r-process production; however, several stars are Ba-enhanced but unusually poor in Sr. Moreover, some of the low-[Fe/H] stars appear to be carbon-enhanced. We interpret the observed abundance patterns with the help of chemical evolution models that demonstrate the need for modest star formation efficiency and low wind efficiency confirming that the progenitor of S2 was a primitive dwarf galaxy.
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    Variable stars in the VVV globular clusters. II. NGC 6441, NGC 6569, NGC 6626 (M 28), NGC 6656 (M 22), 2MASS-GC 02, and Terzan 10
    (2021) Alonso-García, Javier; Smith, Leigh C.; Catelan, Márcio; Minniti, Dante; Navarrete, Camila; Borissova, Jura; Carballo-Bello, Julio A.; Contreras Ramos, Rodrigo; Fernández-Trincado, José G.; Ferreira Lopes, Carlos E.; Gran, Felipe; Garro, Elisa R.; Geisler, Doug; Guo, Zhen; Hempel, Maren; Kerins, Eamonn; Lucas, Philip W.; Palma, Tali; Peña Ramírez, Karla; Ramírez Alegría, Sebastián; Saito, Roberto K.
    Context. The Galactic globular clusters (GGCs) located in the inner regions of the Milky Way suffer from high extinction that makes their observation challenging. High densities of field stars in their surroundings complicate their study even more. The VISTA Variables in the Via Lactea (VVV) survey provides a way to explore these GGCs in the near-infrared where extinction effects are highly diminished. Aims: We conduct a search for variable stars in several inner GGCs, taking advantage of the unique multi-epoch, wide-field, near-infrared photometry provided by the VVV survey. We are especially interested in detecting classical pulsators that will help us constrain the physical parameters of these GGCs. In this paper, the second of a series, we focus on NGC 6656 (M 22), NGC 6626 (M 28), NGC 6569, and NGC 6441; these four massive GGCs have known variable sources, but quite different metallicities. We also revisit 2MASS-GC 02 and Terzan 10, the two GGCs studied in the first paper of this series. Methods: We present an improved method and a new parameter that efficiently identify variable candidates in the GGCs. We also use the proper motions of those detected variable candidates and their positions in the sky and in the color-magnitude diagrams to assign membership to the GGCs. Results: We identify and parametrize in the near-infrared numerous variable sources in the studied GGCs, cataloging tens of previously undetected variable stars. We recover many known classical pulsators in these clusters, including the vast majority of their fundamental mode RR Lyrae. We use these pulsators to obtain distances and extinctions toward these objects. Recalibrated period-luminosity-metallicity relations for the RR Lyrae bring the distances to these GGCs to a closer agreement with those reported by Gaia, except for NGC 6441, which is an uncommon Oosterhoff III GGC. Recovered proper motions for these GGCs also agree with those reported by Gaia, except for 2MASS-GC 02, the most reddened GGC in our sample, where the VVV near-infrared measurements provide a more accurate determination of its proper motions. Lightcurves and full Tables 2, 5, 6, 7, 8, and 9 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/651/A47...