DSpace Angular :: Browsing by Author "Alonso-Garcia, Javier"

Browsing by Author "Alonso-Garcia, Javier"

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Chemical abundances in bright giants of the globular cluster M62 (NGC 6266)^☆
(2014) Yong, David; Brito, Alan Alves; Da Costa, Gary S.; Alonso-Garcia, Javier; Karakas, Amanda I.; Pignatari, Marco; Roederer, Ian U.; Aoki, Wako; Fishlock, Cherie K.; Grundahl, Frank; Norris, John E.
With the exception of Terzan 5, all the Galactic globular clusters that possess significant metallicity spreads, such as omega Cen and M22, are preferentially the more luminous clusters with extended horizontal branches. Here we present radial velocities and chemical abundances for seven bright giants in the globular cluster M62, a previously little-studied cluster. With M-V = -9.18, M62 is the ninth most luminous Galactic globular cluster and has an extended horizontal branch. Within our sample, we find (i) no evidence for a dispersion in metallicity, [Fe/H], beyond the measurement uncertainties, (ii) star-to-star abundance variations for C, O, Na and Al with the usual correlations between these elements as seen in other globular clusters, and (iii) a global enrichment for the elements Zr, Ba and La at the level [X/Fe] similar or equal to +0.4 dex. For elements heavier than La, the abundance ratios are consistent with the scaled-solar r-process distribution. Below La, the abundances are anomalous when compared to the scaled-solar s-process or r-process distributions. For these elements, the abundance signature in M62 is in agreement with predictions of the s-process from fast-rotating massive stars, although the high [Rb/Y] ratio we measure may be a challenge to this scenario.
Confirmation of a New Metal-poor Globular Cluster in the Galactic Bulge
(2018) Minniti, D.; Schlafly, E. F.; Palma, Tali; Claria, Juan J.; Hempel, Maren; Alonso-Garcia, Javier; Bica, Eduardo; Bonatto, Charles; Braga, Vittorio F.; Clementini, Gisella; Garofalo, Alessia; Gomez, Matias; Ivanov, Valentin D.; Lucas, Phill
Deep Hubble Space Telescope Imaging of Globular Clusters toward the Galactic Bulge: Observations, Data Reduction, and Color-magnitude Diagrams
(2018) Cohen, Roger E.; Mauro, Francesco; Alonso-Garcia, Javier; Hempel, Maren; Sarajedini, Ata; Ordonez, Antonio J.; Geisler, Douglas; Kalirai, Jason S.
Discovery of Tidal RR Lyrae Stars in the Bulge Globular Cluster M62
(2018) Minniti, D.; Fernandez-Trincado, Jose G.; Ripepi, Vincenzo; Alonso-Garcia, Javier; Contreras Ramos, Rodrigo Andrés; Marconi, Marcella
MAPPING DIFFERENTIAL REDDENING IN THE INNER GALACTIC GLOBULAR CLUSTER SYSTEM
(2011) Alonso-Garcia, Javier; Mateo, Mario; Sen, Bodhisattva; Banerjee, Moulinath; von Braun, Kaspar
A serious limitation in the study of many globular clusters-especially those located near the Galactic center-has been the existence of large and differential extinction by foreground dust. In a series of papers, we intend to map the differential extinction and remove its effects, using a new dereddening technique, in a sample of clusters in the direction of the inner Galaxy, observed using the Magellan 6.5 m telescope and the Hubble Space Telescope. These observations and their analysis will let us produce high-quality color-magnitude diagrams of these poorly studied clusters that will allow us to determine these clusters' relative ages, distances, and chemistry and to address important questions about the formation and the evolution of the inner Galaxy. We also intend to use the maps of the differential extinction to sample and characterize the interstellar medium along the numerous low-latitude lines of sight where the clusters in our sample lie. In this first paper, we describe in detail our dereddening method along with the powerful statistics tools that allow us to apply it, and we show the kind of results that we can expect, applying the method to M62, one of the clusters in our sample. The width of the main sequence and lower red giant branch narrows by a factor of two after applying our dereddening technique, which will significantly help to constrain the age, distance, and metallicity of the cluster.
Milky Way demographics with the VVV survey IV. PSF photometry from almost one billion stars in the Galactic bulge and adjacent southern disk
(2018) Alonso-Garcia, Javier; Saito, Roberto K.; Hempel, Maren; Minniti, D.; Pullen, Joyce; Catelan, Márcio; Contreras Ramos, Rodrigo Andrés; Cross, Nicholas J.G.; Gonzalez, Oscar A.; Zoccali, Manuela; Lucas, Philip W.; Palma, Tali; Valenti, Elena
Relative ratios and radial distributions of the multiple populations in the Galactic globular clusters
(2015) Alonso-Garcia, Javier; Catelan, Marcio; Amigo, Pía; Contreras Ramos, Rodrigo; Cortés, Cristián; Kuehn, Charles; Grundahl, Frank; López, Graciela; Salinas, Ricardo; Smith, Horace; Stetson, Peter; Sweigart, Allen; Valcarce, Aldo A. R.; Zoccali, Manuela
Recently, the long-standing paradigm that globular clusters are close approximations to simple stellar populations, with all stars formed at precisely the same time from populations having precisely the same chemical composition, has been shattered by a series of photometric and spectroscopic observations that reveal that these objects are more complex than we once thought . In this poster, we present the first results of a survey we are conducting among the Galactic globular clusters using the Strömgren photometric system. We show that the bluest Strömgren filters reveal broadenings or splits in the stellar sequences in the color-magnitude diagrams of the sampled clusters. These features allow us to disentangle successfully the different stellar populations in a given globular cluster, which let us measure their relative ratios, and explore their radial trends and gradients from the cluster center out to its tidal radius....
Stellar Variability in the VVV Survey: Highlights and Current Status
(2015) Catelan, Marcio; Dékány, István; Minniti, Dante; Alonso-Garcia, Javier; Contreras Ramos, Rodrigo; Saito, Roberto; Hajdu, Gergely; Lucas, Phil; Kerins, Eamonn; Hempel, Maren
The Vista Variables in the Via Lactea (VVV) ESO Public Survey consists in a near-infrared time-series survey of the Galactic bulge and inner disk, covering 562 square degrees of the sky, over a total timespan of more than 5 years. In this contribution, we discuss some of our latest results, and provide an updated account of the current status of the survey, especially in the context of stellar variability studies....
The most variable VVV sources: eruptive protostars, dipping giants in the Nuclear Disc and others
(2023) Lucas, Phil; Smith, Leigh; Guo, Zhen; Contreras Peña, Carlos; Minniti, Dante; Miller, Niall; Alonso-Garcia, Javier; Catelan, Marcio; Borissova, J.; Saito, Roberto; Kurtev, Radostin; Navarro, M. G.; Morris, Calum; Muthu, Hariharan; Froebrich, Dirk; Ivanov, Valentin; Bayo, Amelia; Caratti, Alessio; Sanders, Jason
We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) data base of 9.5 yr light curves for variable sources with ΔKs ≥ 4 mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs), and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of ∼2 yr, somewhat slower than the 6–12 month time-scale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P=59 d) similar to KH 15D.
The RR Lyrae projected density distribution from the Galactic centre to the halo
(2021) Gabriela Navarro, Maria; Minniti, Dante; Capuzzo-Dolcetta, Roberto; Alonso-Garcia, Javier; Contreras Ramos, Rodrigo; Majaess, Daniel; Ripepi, Vincenzo
The projected density distribution of type ab RR Lyrae (RRab) stars was characterised from the innermost regions of the Milky Way to the halo, with the aim of placing constraints on the Galaxy's evolution. The compiled sample (N-RRab=64 850) stems from fundamental mode RR Lyrae variables identified by the VVV, OGLE, and Gaia surveys. The distribution is well fitted by three power laws over three radial intervals. In the innermost region (R<2.2) the distribution follows Sigma (RRab[1])proportional to R-0.94 +/- 0.051, while in the external region the distribution adheres to Sigma (RRab[2])proportional to R-1.50 +/- 0.019 for 2.2 degrees< R< 8.0 degrees and Sigma (RRab[3])proportional to R-2.43 +/- 0.043 for 8.0 degrees< R<30.0 degrees. Conversely, the cumulative distribution of red clump (RC) giants exhibits a more concentrated distribution in the mean, but in the central R<2.2 the RRab population is more peaked, whereas globular clusters (GCs) follow a density power law (Sigma (GCs)proportional to R-1.59 +/- 0.060 for R<30.0) similar to that of RRab stars, especially when considering a more metal-poor subsample ([Fe/H] < -1.1 dex). The main conclusion emerging from the analysis is that the RRab distribution favours the star cluster infall and merger scenario for creating an important fraction (> 18%) of the central Galactic region. The radii containing half of the populations (half populations radii) are R-H RRab=6.8 degrees (0.99 kpc), R-H RC=4.2 degrees (0.61 kpc), and R-H GCs=11.9 degrees (1.75 kpc) for the RRab stars, RC giants, and GCs, respectively. Finally, merely similar to 1% of the stars have been actually discovered in the innermost region (R< 35 pc) out of the expected (based on our considerations) total number of RRab therein: N1562. That deficit will be substantially ameliorated with future space missions like the Nancy Grace Roman Space Telescope (formerly WFIRST).
The structure behind the galactic bar traced by red clump stars in the VVV survey
(2018) Gonzalez, Oscar A.; Minniti, D.; Valenti, Elena; Alonso-Garcia, Javier; Debattista, Victor P.; Zoccali, Manuela; Rejkuba, Marina; Dias, Bruno; Surot, Bruno; Hempel, Maren
The VVV Survey RR Lyrae Population in the Galactic Center Region
(2018) Contreras Ramos, Rodrigo Andrés; Minniti, D.; Gran, Felipe; Zoccali, Manuela; Alonso-Garcia, Javier; Huijse, Pablo; Gabriela Navarro, Maria; Rojas-Arriagada, Alvaro; Valenti, Elena
Variable Stars in VVV Globular Clusters
(2015) Contreras Ramos, Rodrigo; Alonso-Garcia, Javier; Minniti, Dante; Catelan, Márcio; Zoccali, Manuela; Gran, Felipe; Dekany, Istvan
The Vista Variables in the Via Lactea (VVV) is an ongoing variability survey observing the central regions of our Galaxy in the near-infrared by means of the VISTA telescope. Numerous (36) inner Galactic globular clusters fall inside the area covered by the VVV survey. Most of these clusters, especially the faintest ones, have been poorly studied in the past due to the difficulties caused by the presence of an elevated extinction and high field stellar densities in their lines of sight. We will present the first results of a search for variable stars we are conducting in some of these clusters. Our main aim is to obtain a better determination of the physical parameters of these globular clusters and put constrains on the formation scenario of our galaxy using the information provided by their variables stars.
WIDE FIELD NEAR-INFRARED PHOTOMETRY OF 12 GALACTIC GLOBULAR CLUSTERS: OBSERVATIONS VERSUS MODELS ON THE RED GIANT BRANCH
(2015) Cohen, Roger E.; Hempel, Maren; Mauro, Francesco; Geisler, Douglas; Alonso-Garcia, Javier; Kinemuchi, Karen
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-K-S 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.

Browsing by Author "Alonso-Garcia, Javier"

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