Browsing by Author "Cohen, Roger E."

Now showing 1 - 11 of 11
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    APOGEE chemical abundances of globular cluster giants in the inner Galaxy
    (2017) Schiavon, Ricardo P.; Johnson, Jennifer A.; Frinchaboy, Peter M.; Zasowski, Gail; Meszaros, Szabolcs; Garcia-Hernandez, D. A.; Cohen, Roger E.; Tang, Baitian; Villanova, Sandro; Geisler, Douglas; Beers, Timothy C.; Fernandez-Trincado, J. G.; Garcia Perez, Ana E.; Lucatello, Sara; Majewski, Steven R.; Martell, Sarah L.; O'Connell, Robert W.; Allende Prieto, Carlos; Bizyaev, Dmitry; Carrera, Ricardo; Lane, Richard R.; Malanushenko, Elena; Malanushenko, Viktor; Munoz, Ricardo R.; Nitschelm, Christian; Oravetz, Daniel; Pan, Kaike; Roman-Lopes, Alexandre; Schultheis, Matthias; Simmons, Audrey
    We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.
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    Chemical Cartography with APOGEE: Multi-element Abundance Ratios
    (2019) Weinberg, David H.; Holtzman, Jon A.; Hasselquist, Sten; Bird, Jonathan C.; Johnson, Jennifer A.; Shetrone, Matthew; Sobeck, Jennifer; Allende Prieto, Carlos; Bizyaev, Dmitry; Carrera, Ricardo; Cohen, Roger E.; Cunha, Katia; Ebelke, Garrett; Fernandez-Trincado, J. G.; Garcia-Hernandez, D. A.; Hayes, Christian R.; Jonsson, Henrik; Lane, Richard R.; Majewski, Steven R.; Malanushenko, Viktor; Meszaros, Szabolcs; Nidever, David L.; Nitschelm, Christian; Pan, Kaike; Rix, Hans-Walter; Rybizki, Jan; Schiavon, Ricardo P.; Schneider, Donald P.; Wilso, John C.; Zamora, Olga
    We map the trends of elemental abundance ratios across the Galactic disk, spanning R = 3-15 kpc and midplane distance vertical bar Z vertical bar = 0-2 kpc, for 15 elements in a sample of 20,485 stars measured by the SDSS/APOGEE survey (O, Na, Mg, Al, Si, P, S, K, Ca, V, Cr, Mn, Fe, Co, Ni). Adopting Mg rather than Fe as our reference element, and separating stars into two populations based on [Fe/Mg], we find that the median trends of [X/Mg] versus [Mg/H] in each population are nearly independent of location in the Galaxy. The full multi-element cartography can be summarized by combining these nearly universal median sequences with our measured metallicity distribution functions and the relative proportions of the low-[Fe/Mg] (high-alpha) and high-[Fe/Mg] (low-alpha) populations, which depend strongly on R and vertical bar Z vertical bar. We interpret the median sequences with a semi-empirical "two-process" model that describes both the ratio of core collapse and Type Ia supernova (SN Ia) contributions to each element and the metallicity dependence of the supernova yields. These observationally inferred trends can provide strong tests of supernova nucleosynthesis calculations. Our results lead to a relatively simple picture of abundance ratio variations in the Milky Way, in which the trends at any location can be described as the sum of two components with relative contributions that change systematically and smoothly across the Galaxy. Deviations from this picture and future extensions to other elements can provide further insights into the physics of stellar nucleosynthesis and unusual events in the Galaxy's history.
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    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.
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    Exploring the Stellar Age Distribution of the Milky Way Bulge Using APOGEE
    (2020) Hasselquist, Sten; Zasowski, Gail; Feuillet, Diane K.; Schultheis, Mathias; Nataf, David M.; Anguiano, Borja; Beaton, Rachael L.; Beers, Timothy C.; Cohen, Roger E.; Cunha, Katia; Fernandez-Trincado, Jose G.; Garcia-Hernandez, D. A.; Geisler, Doug; Holtzman, Jon A.; Johnson, Jennifer; Lane, Richard R.; Majewski, Steven R.; Bidin, Christian Moni; Nitschelm, Christian; Roman-Lopes, Alexandre; Schiavon, Ricardo; Smith, Verne V.; Sobeck, Jennifer
    We present stellar age distributions of the Milky Way bulge region using ages for similar to 6000 high-luminosity (log (g), metal-rich ([Fe/H] >= -0.5) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment. Ages are derived using The Cannon label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars (>8 Gyr). We find evidence that the planar region of the bulge (vertical bar Z(GC)vertical bar <= 0.25 kpc) is enriched in metallicity, Z, at a faster rate (dZ/dt similar to 0.0034 Gyr(-1)) than regions farther from the plane (dZ/dt similar to 0.0013 Gyr(-1) at vertical bar Z(GC)vertical bar > 1.00 kpc). We identify a nonnegligible fraction of younger stars (age similar to 2-5 Gyr) at metallicities of +0.2 < [Fe/H] < +0.4. These stars are preferentially found in the plane (vertical bar Z(GC)vertical bar <= 0.25 kpc) and at R-cy approximate to 2-3 kpc, with kinematics that are more consistent with rotation than are the kinematics of older stars at the same metallicities. We do not measure a significant age difference between stars found inside and outside the bar. These findings show that the bulge experienced an initial starburst that was more intense close to the plane than far from the plane. Then, star formation continued at supersolar metallicities in a thin disk at 2 kpc less than or similar to R-cy less than or similar to 3 kpc until similar to 2 Gyr ago.
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    Final Targeting Strategy for the Sloan Digital Sky Survey IV Apache Point Observatory Galactic Evolution Experiment 2 North Survey
    (2021) Beaton, Rachael L.; Oelkers, Ryan J.; Hayes, Christian R.; Covey, Kevin R.; Chojnowski, S. D.; De Lee, Nathan; Sobeck, Jennifer S.; Majewski, Steven R.; Cohen, Roger E.; Fernandez-Trincado, Jose; Longa-Pena, Penelope; O'Connell, Julia E.; Santana, Felipe A.; Stringfellow, Guy S.; Zasowski, Gail; Aerts, Conny; Anguiano, Borja; Bender, Chad; Canas, Caleb I.; Cunha, Katia; Donor, John; Fleming, Scott W.; Frinchaboy, Peter M.; Feuillet, Diane; Harding, Paul; Hasselquist, Sten; Holtzman, Jon A.; Johnson, Jennifer A.; Kollmeier, Juna A.; Kounkel, Marina; Mahadevan, Suvrath; Price-Whelan, Adrian. M.; Rojas-Arriagada, Alvaro; Roman-Zuniga, Carlos; Schlafly, Edward F.; Schultheis, Mathias; Shetrone, Matthew; Simon, Joshua D.; Stassun, Keivan G.; Stutz, Amelia M.; Tayar, Jamie; Teske, Johanna; Tkachenko, Andrew; Troup, Nicholas; Albareti, Franco D.; Bizyaev, Dmitry; Bovy, Jo; Burgasser, Adam J.; Comparat, Johan; Downes, Juan Jose; Geisler, Doug; Inno, Laura; Manchado, Arturo; Ness, Melissa K.; Pinsonneault, Marc H.; Prada, Francisco; Roman-Lopes, Alexandre; Simonian, Gregory V. A.; Smith, Verne V.; Yan, Renbin; Zamora, Olga
    The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is a dual-hemisphere, near-infrared (NIR), spectroscopic survey with the goal of producing a chemodynamical mapping of the Milky Way. The targeting for APOGEE-2 is complex and has evolved with time. In this paper, we present the updates and additions to the initial targeting strategy for APOGEE-2N presented in Zasowski et al. (2017). These modifications come in two implementation modes: (i) "Ancillary Science Programs" competitively awarded to Sloan Digital Sky Survey IV PIs through proposal calls in 2015 and 2017 for the pursuit of new scientific avenues outside the main survey, and (ii) an effective 1.5 yr expansion of the survey, known as the Bright Time Extension (BTX), made possible through accrued efficiency gains over the first years of the APOGEE-2N project. For the 23 distinct ancillary programs, we provide descriptions of the scientific aims, target selection, and how to identify these targets within the APOGEE-2 sample. The BTX permitted changes to the main survey strategy, the inclusion of new programs in response to scientific discoveries or to exploit major new data sets not available at the outset of the survey design, and expansions of existing programs to enhance their scientific success and reach. After describing the motivations, implementation, and assessment of these programs, we also leave a summary of lessons learned from nearly a decade of APOGEE-1 and APOGEE-2 survey operations. A companion paper, F. Santana et al. (submitted; AAS29036), provides a complementary presentation of targeting modifications relevant to APOGEE-2 operations in the Southern Hemisphere.
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    How many components? Quantifying the complexity of the metallicity distribution in the Milky Way bulge with APOGEE
    (2020) Rojas-Arriagada, Alvaro; Zasowski, Gail; Schultheis, Mathias; Zoccali, Manuela; Hasselquist, Sten; Chiappini, Cristina; Cohen, Roger E.; Cunha, Katia; Fernandez-Trincado, Jose G.; Fragkoudi, Francesca; Garcia-Hernandez, D. A.; Geisler, Doug; Gran, Felipe; Lian, Jianhui; Majewski, Steven; Minniti, Dante; Monachesi, Antonela; Nitschelm, Christian; Queiroz, Anna B. A.
    We use data of similar to 13 000 stars from the Sloan Digital Sky Survey/Apache Point Observatory Galactic Evolution Experiment survey to study the shape of the bulge metallicity distribution function (MDF) within the region vertical bar l vertical bar <= 11 degrees and vertical bar b vertical bar = 13 degrees, and spatially constrained to R-GC <= 3.5 kpc. We apply Gaussian mixture modelling and non-negative matrix factorization decomposition techniques to identify the optimal number and the properties of MDF components. We find that the shape and spatial variations of the MDF (at [Fe/H] >= -1 dex) are well represented as a smoothly varying contribution of three overlapping components located at [Fe/H] = +0.32, -0.17, and -0.66 dex. The bimodal MDF found in previous studies is in agreement with our trimodal assessment once the limitations in sample size and individual measurement errors are taken into account. The shape of the MDF and its correlations with kinematics reveal different spatial distributions and kinematical structure for the three components co-existing in the bulge region. We confirm the consensus physical interpretation of metal-rich stars as associated with the secularly evolved disc into a boxy/peanut X-shape bar. On the other hand, metal-intermediate stars could be the product of in-situ formation at high redshift in a gas-rich environment characterized by violent and fast star formation. This interpretation would help us to link a present-day structure with those observed in formation in the centre of high-redshift galaxies. Finally, metal-poor stars may correspond to the metal-rich tail of the population sampled at lower metallicity from the study of RR Lyrae stars. Conversely, they could be associated with the metal-poor tail of the early thick disc.
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    Strong chemical tagging with APOGEE: 21 candidate star clusters that have dissolved across the Milky Way disc
    (2020) Price-Jones, Natalie; Bovy, Jo; Webb, Jeremy J.; Prieto, Carlos Allende; Beaton, Rachael; Brownstein, Joel R.; Cohen, Roger E.; Cunha, Katia; Donor, John; Frinchaboy, Peter M.; Garcia-Hernandez, D. A.; Lane, Richard R.; Majewski, Steven R.; Nidever, David L.; Roman-Lopes, Alexandre
    Chemically tagging groups of stars born in the same birth cluster is a major goal of spectroscopic surveys. To investigate the feasibility of such strong chemical tagging, we perform a blind chemical tagging experiment on abundances measured from APOGEE survey spectra. We apply a density-based clustering algorithm to the 8D chemical space defined by [Mg/Fe], [Al/Fe], [Si/Fe], [K/Fe], [Ti/Fe], [Mn/Fe], [Fe/H], and [Ni/Fe], abundances ratios which together span multiple nucleosynthetic channels. In a high-quality sample of 182 538 giant stars, we detect 21 candidate clusterswith more than 15 members. Our candidate clusters are more chemically homogeneous than a population of non-member stars with similar [Mg/Fe] and [Fe/H], even in abundances not used for tagging. Group members are consistent with having the same age and fall along a single stellar-population track in log g versus T-eff space. Each group's members are distributed over multiple kpc, and the spread in their radial and azimuthal actions increases with age. We qualitatively reproduce this increase using N-body simulations of cluster dissolution in Galactic potentials that include transient winding spiral arms. Observing our candidate birth clusters with high-resolution spectroscopy in other wavebands to investigate their chemical homogeneity in other nucleosynthetic groups will be essential to confirming the efficacy of strong chemical tagging. Our initially spatially compact but now widely dispersed candidate clusters will provide novel limits on chemical evolution and orbital diffusion in the Galactic disc, and constraints on star formation in loosely bound groups.
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    The metal-poor non-sagittarius (?) globular cluster NGC 5053 : orbit and Mg, Al, and Si abundances
    (2018) Baitian Tang, D.; Fernández Trincado, J. G.; Geisler, Doug; Zamora, Olga; Mészáros, Szabolcs; Masseron, Thomas; Cohen, Roger E.; García Hernández, D. A.; Lane, Richard R.; Minniti, D.
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    The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data
    (2022) Abdurro'uf; Accetta, Katherine; Aerts, Conny; Aguirre, Victor Silva; Ahumada, Romina; Ajgaonkar, Nikhil; Ak, N. Filiz; Alam, Shadab; Prieto, Carlos Allende; Almeida, Andres; Anders, Friedrich; Anderson, Scott F.; Andrews, Brett H.; Anguiano, Borja; Aquino-Ortiz, Erik; Aragon-Salamanca, Alfonso; Argudo-Fernandez, Maria; Ata, Metin; Aubert, Marie; Avila-Reese, Vladimir; Badenes, Carles; Barba, Rodolfo H.; Barger, Kat; Barrera-Ballesteros, Jorge K.; Beaton, Rachael L.; Beers, Timothy C.; Belfiore, Francesco; Bender, Chad F.; Bernardi, Mariangela; Bershady, Matthew A.; Beutler, Florian; Bidin, Christian Moni; Bird, Jonathan C.; Bizyaev, Dmitry; Blanc, Guillermo A.; Blanton, Michael R.; Boardman, Nicholas Fraser; Bolton, Adam S.; Boquien, Mederic; Borissova, Jura; Bovy, Jo; Brandt, W. N.; Brown, Jordan; Brownstein, Joel R.; Brusa, Marcella; Buchner, Johannes; Bundy, Kevin; Burchett, Joseph N.; Bureau, Martin; Burgasser, Adam; Cabang, Tuesday K.; Campbell, Stephanie; Cappellari, Michele; Carlberg, Joleen K.; Wanderley, Fabio Carneiro; Carrera, Ricardo; Cash, Jennifer; Chen, Yan-Ping; Chen, Wei-Huai; Cherinka, Brian; Chiappini, Cristina; Choi, Peter Doohyun; Chojnowski, S. Drew; Chung, Haeun; Clerc, Nicolas; Cohen, Roger E.; Comerford, Julia M.; Comparat, Johan; da Costa, Luiz; Covey, Kevin; Crane, Jeffrey D.; Cruz-Gonzalez, Irene; Culhane, Connor; Cunha, Katia; Dai, Y. Sophia; Damke, Guillermo; Darling, Jeremy; Davidson, James W., Jr.; Davies, Roger; Dawson, Kyle; De Lee, Nathan; Diamond-Stanic, Aleksandar M.; Cano-Diaz, Mariana; Sanchez, Helena Dominguez; Donor, John; Duckworth, Chris; Dwelly, Tom; Eisenstein, Daniel J.; Elsworth, Yvonne P.; Emsellem, Eric; Eracleous, Mike; Escoffier, Stephanie; Fan, Xiaohui; Farr, Emily; Feng, Shuai; Fernandez-Trincado, Jose G.; Feuillet, Diane; Filipp, Andreas; Fillingham, Sean P.; Frinchaboy, Peter M.; Fromenteau, Sebastien; Galbany, Lluis; Garcia, Rafael A.; Garcia-Hernandez, D. A.; Ge, Junqiang; Geisler, Doug; Gelfand, Joseph; Geron, Tobias; Gibson, Benjamin J.; Goddy, Julian; Godoy-Rivera, Diego; Grabowski, Kathleen; Green, Paul J.; Greener, Michael; Grier, Catherine J.; Griffith, Emily; Guo, Hong; Guy, Julien; Hadjara, Massinissa; Harding, Paul; Hasselquist, Sten; Hayes, Christian R.; Hearty, Fred; Hill, Lewis; Hogg, David W.; Holtzman, Jon A.; Horta, Danny; Hsieh, Bau-Ching; Hsu, Chin-Hao; Hsu, Yun-Hsin; Huber, Daniel; Huertas-Company, Marc; Hutchinson, Brian; Hwang, Ho Seong; Ibarra-Medel, Hector J.; Chitham, Jacob Ider; Ilha, Gabriele S.; Imig, Julie; Jaekle, Will; Jayasinghe, Tharindu; Ji, Xihan; Johnson, Jennifer A.; Jones, Amy; Jonsson, Henrik; Katkov, Ivan; Khalatyan, Arman; Kinemuchi, Karen; Kisku, Shobhit; Knapen, Johan H.; Kneib, Jean-Paul; Kollmeier, Juna A.; Kong, Miranda; Kounkel, Marina; Kreckel, Kathryn; Krishnarao, Dhanesh; Lacerna, Ivan; Lane, Richard R.; Langgin, Rachel; Lavender, Ramon; Law, David R.; Lazarz, Daniel; Leung, Henry W.; Leung, Ho-Hin; Lewis, Hannah M.; Li, Cheng; Li, Ran; Lian, Jianhui; Liang, Fu-Heng; Lin, Lihwai; Lin, Yen-Ting; Lin, Sicheng; Lintott, Chris; Long, Dan; Longa-Pena, Penelope; Lopez-Coba, Carlos; Lu, Shengdong; Lundgren, Britt F.; Luo, Yuanze; Mackereth, J. Ted; de la Macorra, Axel; Mahadevan, Suvrath; Majewski, Steven R.; Manchado, Arturo; Mandeville, Travis; Maraston, Claudia; Margalef-Bentabol, Berta; Masseron, Thomas; Masters, Karen L.; Mathur, Savita; McDermid, Richard M.; Mckay, Myles; Merloni, Andrea; Merrifield, Michael; Meszaros, Szabolcs; Miglio, Andrea; Di Mille, Francesco; Minniti, Dante; Minsley, Rebecca; Monachesi, Antonela; Moon, Jeongin; Mosser, Benoit; Mulchaey, John; Muna, Demitri; Munoz, Ricardo R.; Myers, Adam D.; Myers, Natalie; Nadathur, Seshadri; Nair, Preethi; Nandra, Kirpal; Neumann, Justus; Newman, Jeffrey A.; Nidever, David L.; Nikakhtar, Farnik; Nitschelm, Christian; O'Connell, Julia E.; Garma-Oehmichen, Luis; de Oliveira, Gabriel Luan Souza; Olney, Richard; Oravetz, Daniel; Ortigoza-Urdaneta, Mario; Osorio, Yeisson; Otter, Justin; Pace, Zachary J.; Padilla, Nelson; Pan, Kaike; Pan, Hsi-An; Parikh, Taniya; Parker, James; Peirani, Sebastien; Ramirez, Karla Pena; Penny, Samantha; Percival, Will J.; Perez-Fournon, Ismael; Pinsonneault, Marc; Poidevin, Frederick; Poovelil, Vijith Jacob; Price-Whelan, Adrian M.; Queiroz, Anna Barbara de Andrade; Raddick, M. Jordan; Ray, Amy; Rembold, Sandro Barboza; Riddle, Nicole; Riffel, Rogemar A.; Riffel, Rogerio; Rix, Hans-Walter; Robin, Annie C.; Rodriguez-Puebla, Aldo; Roman-Lopes, Alexandre; Roman-Zuniga, Carlos; Rose, Benjamin; Ross, Ashley J.; Rossi, Graziano; Rubin, Kate H. R.; Salvato, Mara; Sanchez, Sebastian F.; Sanchez-Gallego, Jose R.; Sanderson, Robyn; Rojas, Felipe Antonio Santana; Sarceno, Edgar; Sarmiento, Regina; Sayres, Conor; Sazonova, Elizaveta; Schaefer, Adam L.; Schiavon, Ricardo; Schlegel, David J.; Schneider, Donald P.; Schultheis, Mathias; Schwope, Axel; Serenelli, Aldo; Serna, Javier; Shao, Zhengyi; Shapiro, Griffin; Sharma, Anubhav; Shen, Yue; Shetrone, Matthew; Shu, Yiping; Simon, Joshua D.; Skrutskie, M. F.; Smethurst, Rebecca; Smith, Verne; Sobeck, Jennifer; Spoo, Taylor; Sprague, Dani; Stark, David, V; Stassun, Keivan G.; Steinmetz, Matthias; Stello, Dennis; Stone-Martinez, Alexander; Storchi-Bergmann, Thaisa; Stringfellow, Guy S.; Stutz, Amelia; Su, Yung-Chau; Taghizadeh-Popp, Manuchehr; Talbot, Michael S.; Tayar, Jamie; Telles, Eduardo; Teske, Johanna; Thakar, Ani; Theissen, Christopher; Tkachenko, Andrew; Thomas, Daniel; Tojeiro, Rita; Toledo, Hector Hernandez; Troup, Nicholas W.; Trump, Jonathan R.; Trussler, James; Turner, Jacqueline; Tuttle, Sarah; Unda-Sanzana, Eduardo; Vazquez-Mata, Jose Antonio; Valentini, Marica; Valenzuela, Octavio; Vargas-Gonzalez, Jaime; Vargas-Magana, Mariana; Alfaro, Pablo Vera; Villanova, Sandro; Vincenzo, Fiorenzo; Wake, David; Warfield, Jack T.; Washington, Jessica Diane; Weaver, Benjamin Alan; Weijmans, Anne-Marie; Weinberg, David H.; Weiss, Achim; Westfall, Kyle B.; Wild, Vivienne; Wilde, Matthew C.; Wilson, John C.; Wilson, Robert F.; Wilson, Mikayla; Wolf, Julien; Wood-Vasey, W. M.; Yan, Renbin; Zamora, Olga; Zasowski, Gail; Zhang, Kai; Zhao, Cheng; Zheng, Zheng; Zheng, Zheng; Zhu, Kai
    This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys.
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    Two groups of red giants with distinct chemical abundances in the bulge globular cluster NGC 6553 through the eyes of APOGEE
    (OXFORD UNIV PRESS, 2017) Tang, Baitian; Cohen, Roger E.; Geisler, Doug; Schiavon, Ricardo P.; Majewski, Steven R.; Villanova, Sandro; Carrera, Ricardo; Zamora, Olga; Garcia Hernandez, D. A.; Shetrone, Matthew; Frinchaboy, Peter; Meza, Andres; Fernandez Trincado, J. G.; Munoz, Ricardo R.; Lin, Chien Cheng; Lane, Richard R.; Nitschelm, Christian; Pan, Kaike; Bizyaev, Dmitry; Oravetz, Daniel; Simmons, Audrey
    Multiple populations revealed in globular clusters (GCs) are important windows to the formation and evolution of these stellar systems. The metal-rich GCs in the Galactic bulge are an indispensable part of this picture, but the high optical extinction in this region has prevented extensive research. In this work, we use the high-resolution near-infrared (NIR) spectroscopic data from Apache Point Observatory Galactic Evolution Experiment (APOGEE) to study the chemical abundances of NGC 6553, which is one of the most metal-rich bulge GCs. We identify 10 red giants as cluster members using their positions, radial velocities, iron abundances, and NIR photometry. Our sample stars show a mean radial velocity of -0.14 +/- 5.47 km s(-1), land a mean [Fe/H] of -0.15 +/- 0.05. We clearly separate two populations of stars in C and N in this GC for the first time. NGC 6553 is the most metal-rich GC where the multiple stellar population phenomenon is found until now. Substantial chemical variations are also found in Na, O, and Al. However, the two populations show similar Si, Ca, and iron-peak element abundances. Therefore, we infer that the CNO, NeNa, and MgAl cycles have been activated, but the MgAl cycle is too weak to show its effect on Mg. Type Ia and Type II supernovae do not seem to have significantly polluted the second generation stars. Comparing with other GC studies, NGC 6553 shows similar chemical variations as other relatively metal-rich GCs. We also confront current GC formation theories with our results, and suggest possible avenues for improvement in the models.
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    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.