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Medium-resolution Spectroscopy of Red Giant Branch Stars in<i>ω</i>Centauri
An, Deokkeun,Lee, Young Sun,Jung, Jae In,Rey, Soo-Chang,Rhee, Jaehyon,Lee, Jae-Woo,Lee, Young-Wook,Joe, Young Hoon American Institute of Physics 2017 The Astronomical journal Vol.154 No.4
<P>We present [Fe/H] and [Ca/Fe] of similar to 600 red giant branch (RGB) members of the globular cluster Omega Centauri (omega Cen). We collect medium-resolution (R similar to 2000) spectra using the Blanco 4 m telescope at the Cerro Tololo Inter-American Observatory equipped with Hydra, the fiber-fed multi-object spectrograph. We demonstrate that blending of stellar light in optical fibers severely limits the accuracy of spectroscopic parameters in the crowded central region of the cluster. When photometric temperatures are taken in the spectroscopic analysis, our kinematically selected cluster members, excluding those that are strongly affected by flux from neighboring stars, include relatively fewer stars at intermediate metallicity ([Fe/H] similar to -1.5) than seen in the previous high-resolution survey for brighter giants in Johnson & Pilachowski. As opposed to the trend of increasing [Ca/Fe] with [Fe/H] found by those authors, our [Ca/Fe] estimates, based on Ca II H & K measurements, show essentially the same mean [Ca/Fe] for most of the metal-poor and metal-intermediate populations in this cluster, suggesting that mass- or metallicity-dependent SN II yields may not be necessary in their proposed chemical evolution scenario. Metal-rich cluster members in our sample show a large spread in [Ca/Fe], and do not exhibit a clear bimodal distribution in [Ca/Fe]. We also do not find convincing evidence for a radial metallicity gradient among RGB stars in omega Cen.</P>
ULTRAVIOLET PROPERTIES OF GALACTIC GLOBULAR CLUSTERS WITH GALEX. I. THE COLOR-MAGNITUDE DIAGRAMS
Schiavon, Ricardo P.,Dalessandro, Emanuele,Sohn, Sangmo T.,Rood, Robert T.,O'Connell, Robert W.,Ferraro, Francesco R.,Lanzoni, Barbara,Beccari, Giacomo,Rey, Soo-Chang,Rhee, Jaehyon,Rich, R. Michael,Yo American Institute of Physics 2012 The Astronomical journal Vol.143 No.5
<P>We present Galaxy Evolution Explorer (GALEX) data for 44 Galactic globular clusters (GCs) obtained during three GALEX observing cycles between 2004 and 2008. This is the largest homogeneous data set on the UV photometric properties of Galactic GCs ever collected. The sample selection and photometric analysis are discussed, and color-magnitude diagrams (CMDs) are presented. The blue and intermediate-blue horizontal branch is the dominant feature of the UV CMDs of old Galactic GCs. Our sample is large enough to display the remarkable variety of horizontal branch shapes found in old stellar populations. Other stellar types that are obviously detected are blue stragglers and post-core-He burning stars. The main features of UV CMDs of Galactic GCs are briefly discussed. We establish the locus of post-core-He burning stars in the UV CMD and present a catalog of candidate asymptotic giant branch (AGB), AGB-manqué, post early-AGB, and post-AGB stars within our cluster sample.</P>