Abstract
We present [Fe/H] and [Ca/Fe] of ∼600 red giant branch (RGB) members of the globular cluster Omega Centauri (ω Cen). We collect medium-resolution (R ∼ 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] ∼ -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 .
| Original language | English |
|---|---|
| Article number | aa8364 |
| Journal | Astronomical Journal |
| Volume | 154 |
| Issue number | 4 |
| DOIs | |
| Publication status | Published - 2017 Oct |
Bibliographical note
Funding Information:Visiting astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.
Funding Information:
IRAF (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation.
Funding Information:
We thank the referee for helpful comments and suggestions. D.A. and J.I.J. thank Dongwook Lim for useful discussions on calcium index measurements. Support for this work was provided by the National Research Foundation (NRF) of Korea to the Center for Galaxy Evolution Research (No. 2010-0027910). D.A. and J.I.J. acknowledge partial support provided by the Basic Science Research Program through the NRF of Korea funded by the Ministry of Education (NRF-2015R1D1A1A09058700). This work was developed from a master’s thesis conducted by J.I.J. under the supervision of D.A. Y.S.L. acknowledges support provided by the Basic Science Research Program through the NRF of Korea funded by the Ministry of Science, ICT & Future Planning (NRF-2015R1C1A1A02036658). S.C.R. acknowledges support provided by the Basic Science Research Program through the NRF of Korea funded by the Ministry of Education, Science, and Technology (NRF-2015R1A2A2A01006828).
Funding Information:
This work is based on observations at the Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO Prop. ID: 2005A-0166; PI: S. C. Rey), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation.
Publisher Copyright:
© 2017. The American Astronomical Society. All rights reserved.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science