Browsing by Author "Cohen, R. E."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
- ItemBaade's window and APOGEE Metallicities, ages, and chemical abundances(2017) Schultheis, M.; Rojas Arriagada, Alvaro; Pérez, A. E. García; Jönsson, H.; Hayden, M.; Nandakumar, G.; Cunha, K.; Prieto, C. Allende; Holtzman, J. A.; Beers, T. C.; Bizyaev, D.; Brinkmann, J.; Carrera, R.; Cohen, R. E.; Geisler, D.; Hearty, F. R.; Fernández-Trincado, J. G.; Maraston, C.; Minniti, D.; Nitschelm, C.; Roman-Lopes, A.; Schneider, D. P.; Tang, B.; Villanova, S.; Zasowski, G.; Majewski, S. R.
- ItemCAPOS: The bulge Cluster APOgee Survey. I. Overview and initial ASPCAP results(2021) Geisler, D.; Villanova, S.; O'Connell, J. E.; Cohen, R. E.; Moni Bidin, C.; Fernández-Trincado, J. G.; Muñoz, C.; Minniti, D.; Zoccali, M.; Rojas-Arriagada, A.; Contreras Ramos, R.; Catelan, Márcio; Mauro, F.; Cortés, C.; Ferreira Lopes, C. E.; Arentsen, A.; Starkenburg, E.; Martin, N. F.; Tang, B.; Parisi, C.; Alonso-García, J.; Gran, F.; Cunha, K.; Smith, V.; Majewski, S. R.; Jönsson, H.; García-Hernández, D. A.; Horta, D.; Mészáros, S.; Monaco, L.; Monachesi, A.; Muñoz, R. R.; Brownstein, J.; Beers, T. C.; Lane, R. R.; Barbuy, B.; Sobeck, J.; Henao, L.; González-Díaz, D.; Miranda, R. E.; Reinarz, Y.; Santander, T. A.Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. However, until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools. Aims: CAPOS, the bulge Cluster APOgee Survey, addresses this key topic by observing a large number of BGCs, most of which have only been poorly studied previously. Even their most basic parameters, such as metallicity, [α/Fe], and radial velocity, are generally very uncertain. We aim to obtain accurate mean values for these parameters, as well as abundances for a number of other elements, and explore multiple populations. In this first paper, we describe the CAPOS project and present initial results for seven BGCs. Methods: CAPOS uses the APOGEE-2S spectrograph observing in the H band to penetrate obscuring dust toward the bulge. For this initial paper, we use abundances derived from ASPCAP, the APOGEE pipeline. Results: We derive mean [Fe/H] values of −0.85 ± 0.04 (Terzan 2), −1.40 ± 0.05 (Terzan 4), −1.20 ± 0.10 (HP 1), −1.40 ± 0.07 (Terzan 9), −1.07 ± 0.09 (Djorg 2), −1.06 ± 0.06 (NGC 6540), and −1.11 ± 0.04 (NGC 6642) from three to ten stars per cluster. We determine mean abundances for eleven other elements plus the mean [α/Fe] and radial velocity. CAPOS clusters significantly increase the sample of well-studied Main Bulge globular clusters (GCs) and also extend them to lower metallicity. We reinforce the finding that Main Bulge and Main Disk GCs, formed in situ, have [Si/Fe] abundances slightly higher than their accreted counterparts at the same metallicity. We investigate multiple populations and find our clusters generally follow the light-element (anti)correlation trends of previous studies of GCs of similar metallicity. We finally explore the abundances of the iron-peak elements Mn and Ni and compare their trends with field populations. Conclusions: CAPOS is proving to be an unprecedented resource for greatly improving our knowledge of the formation and evolution of BGCs and the bulge itself....
- ItemFSR 1716: A New Milky Way Globular Cluster Confirmed Using VVV RR Lyrae Stars(2017) Hempel, Maren; Catelan, Márcio; Carballo Bello, J. A.; Ramos, R. C.; Gran, F.; Hagdu, G.; Navarrete, C.; Zoccali, Manuela; Minniti, D.; Palma, T.; Dekany, Istvan; Rejkuba, M.; Pullen, J.; Alonso Garcia, J.; Barba, R.; Barbuy, B.; Bica, E.; Borissova, J.; Chene, A. N.; Claria, J. J.; Cohen, R. E.; Dias, B.; Emerson, J.
- ItemH-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia(2019) Fernandez-Trincado, J. G.; Zamora, O.; Souto, Diogo; Cohen, R. E.; Agli, F. Dell; Garcia-Hernandez, D. A.; Masseron, T.; Schiavon, R. P.; Meszaros, Sz; Cunha, K.; Hasselquist, S.; Shetrone, M.; Schiappacasse Ulloa, J.; Tang, B.; Geisler, D.; Schleicher, D. R. G.; Villanova, S.; Mennickent, R. E.; Minniti, D.; Alonso-Garcia, J.; Manchado, A.; Beers, T. C.; Sobeck, J.; Zasowski, G.; Schultheis, M.; Majewski, S. R.; Rojas-Arriagada, A.; Almeida, A.; Santana, F.; Oelkers, R. J.; Longa-Pena, P.; Carrera, R.; Burgasser, A. J.; Lane, R. R.; Roman-Lopes, A.; Ivans, I. I.; Hearty, F. R.We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.
- ItemInfrared photometry and CaT spectroscopy of globular cluster M 28 (NGC 6626)(2021) Moni Bidin, C.; Mauro, F.; Contreras Ramos, R.; Zoccali, M.; Reinarz, Y.; Moyano, M.; Gonzalez-Diaz, D.; Villanova, S.; Carraro, G.; Borissova, J.; Chene, A-N; Cohen, R. E.; Geisler, D.; Kurtev, R.; Minniti, D.Context. Recent studies show that the inner Galactic regions host genuine bulge globular clusters, but also halo intruders, complex remnants of primordial building blocks, and objects likely accreted during major merging events.Aims. In this study we focus on the properties of M 28, a very old and massive cluster currently located in the Galactic bulge.Methods. We analysed wide-field infrared photometry collected by the VVV survey, VVV proper motions, and intermediate-resolution spectra in the calcium triplet range for 113 targets in the cluster area.Results. Our results in general confirm previous estimates of the cluster properties available in the literature. We find no evidence of differences in metallicity between cluster stars, setting an upper limit of
- ItemThe bimodal [Mg/Fe] versus [Fe/H] bulge sequence as revealed by APOGEE DR14(2019) Rojas-Arriagada, A.; Zoccali, M.; Schultheis, M.; Recio-Blanco, A.; Zasowski, G.; Minniti, D.; Jonsson, H.; Cohen, R. E.Context. The Galactic bulge has a bimodal metallicity distribution function: different kinematic, spatial, and, potentially, age distributions characterize the metal-poor and metal-rich components. Despite this observed dichotomy, which argues for different formation channels for those stars, the distribution of bulge stars in the alpha-abundance versus metallicity plane has been found so far to be a rather smooth single sequence.
- ItemThe Milky Way bar and bulge revealed by APOGEE and Gaia EDR3(2021) Queiroz, A. B. A.; Chiappini, C.; Perez-Villegas, A.; Khalatyan, A.; Anders, F.; Barbuy, B.; Santiago, B. X.; Steinmetz, M.; Cunha, K.; Schultheis, M.; Majewski, S. R.; Minchev, I; Minniti, D.; Beaton, R. L.; Cohen, R. E.; da Costa, L. N.; Fernandez-Trincado, J. G.; Garcia-Hernandez, D. A.; Geisler, D.; Hasselquist, S.; Lane, R. R.; Nitschelm, C.; Rojas-Arriagada, A.; Roman-Lopes, A.; Smith, V; Zasowski, G.We investigate the inner regions of the Milky Way using data from APOGEE and Gaia EDR3. Our inner Galactic sample has more than 26 500 stars within |X-Gal|< 5 kpc, |Y-Gal|< 3.5 kpc, |Z(Gal)|< 1 kpc, and we also carry out the analysis for a foreground-cleaned subsample of 8000 stars that is more representative of the bulge-bar populations. These samples allow us to build chemo-dynamical maps of the stellar populations with vastly improved detail. The inner Galaxy shows an apparent chemical bimodality in key abundance ratios [alpha/Fe], [C/N], and [Mn/O], which probe different enrichment timescales, suggesting a star formation gap (quenching) between the high- and low-alpha populations. Using a joint analysis of the distributions of kinematics, metallicities, mean orbital radius, and chemical abundances, we can characterize the different populations coexisting in the innermost regions of the Galaxy for the first time. The chemo-kinematic data dissected on an eccentricity-|Z|(max) plane reveal the chemical and kinematic signatures of the bar, the thin inner disc, and an inner thick disc, and a broad metallicity population with large velocity dispersion indicative of a pressure-supported component. The interplay between these different populations is mapped onto the different metallicity distributions seen in the eccentricity-|Z|(max) diagram consistently with the mean orbital radius and V-phi distributions. A clear metallicity gradient as a function of |Z|(max) is also found, which is consistent with the spatial overlapping of different populations. Additionally, we find and chemically and kinematically characterize a group of counter-rotating stars that could be the result of a gas-rich merger event or just the result of clumpy star formation during the earliest phases of the early disc that migrated into the bulge. Finally, based on 6D information, we assign stars a probability value of being on a bar orbit and find that most of the stars with large bar orbit probabilities come from the innermost 3 kpc, with a broad dispersion of metallicity. Even stars with a high probability of belonging to the bar show chemical bimodality in the [alpha/Fe] versus [Fe/H] diagram. This suggests bar trapping to be an efficient mechanism, explaining why stars on bar orbits do not show a significant, distinct chemical abundance ratio signature.
- ItemThe Strikingly Metal-rich Halo of the Sombrero Galaxy(2020) Cohen, R. E.; Goudfrooij, P.; Correnti, M.; Gnedin, O. Y.; Harris, W. E.; Chandar, R.; Puzia, Thomas H.; Sánchez Janssen, R.