Browsing by Author "Navarrete, Camila"
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- ItemElevated 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.
- ItemPulsating stars in ω Centauri. Near-IR properties and period-luminosity relations(2017) Navarrete, Camila; Catelan, Marcio; Contreras Ramos, Rodrigo; Alonso-García, Javier; Gran, Felipe; Dékány, István; Minniti, Danteω Centauri (NGC 5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands....
- ItemRR Lyrae stars as tracers of halo substructures(2017) Duffau, Sonia; Vivas, A. Katherina; Navarrete, Camila; Carballo-Bello, Julio; Hajdu, Gergel; Catelan, MarcioThree 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....
- ItemSearching for fossil remnants in the Galactic halo: photometric follow-up of southern CRTScandidates(2015) Chan, Siukuen Josephine; Navarrete, Camila; Catelan, Marcio; Duffau, Sonia; Torrealba, Gabriel. I.; Drake, Andrew J.; Belokurov, Vasily; Koposov, SergeyObservations of the fossil record of the early formation stages of the Milky Way galaxy provide important constraints on cosmological scenarios for the formation of large galaxies like our own. While the northern celestial hemisphere has been extensively examined for the presence and degree of halo substructure, the southern halo has until recently remained "terra incognita" for such studies. However, based on RR Lyrae stars detected in the course of the Catalina Real-time Transients Survey (CRTS), our team has identified a number of new candidate overdensities in the southern Galactic halo (Torrealba et al. 2015, MNRAS, 446, 2251). Here we describe some preliminary results of a deeper search for the Torrealba et al. overdensity candidates, using photometric data from selected wide-field surveys that have mapped the immediate vicinity of some of the more promising among these candidates....
- ItemSignatures of tidal disruption in the Milky Way globular cluster NGC 6981 (M72)(2021) Piatti, Andres E.; Mestre, Martin F.; Carballo-Bello, Julio A.; Carpintero, Daniel D.; Navarrete, Camila; Mora, Marcelo D.; Cenzano, CarolinaWe study the outer regions of the Milky Way globular cluster NGC 6981 based on publicly available BV photometry and new Dark Energy Camera (DECam) observations, both of which reach nearly 4 mag below the cluster main sequence (MS) turnoff. While the BV data sets reveal the present of extra-tidal features around the cluster, the much larger field of view of the DECam observations allowed us to identify some other tidal features, which extend from the cluster toward the opposite direction to the Milky Way center. Such structural features of clusters arise from stellar density maps built using MS stars, following a cleaning of the cluster color-magnitude diagram to remove the contamination of field stars. We also performed N-body simulations in order to help us to understand the spatial distribution of the extra-tidal debris. The outcomes reveal the presence of long trailing and leading tails that are mostly parallel to the direction of the cluster velocity vector. We find that the cluster loses most of its mass by tidal disruption during its perigalactic passages, each of which lasted nearly 20 Myr. Hence, a decrease in the density of escaping stars near the cluster is expected from our N-body simulations, which, in turn, means that stronger extra-tidal features could be found by exploring much larger areas around NGC 6891.
- ItemThe 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, ZhenThe 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.
- ItemVariable 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...