Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri

Deokkeun An, Young Sun Lee, Jae In Jung, Soo Chang Rey, Jaehyon Rhee, Jae Woo Lee, Young Wook Lee, Young Hoon Joe

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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 languageEnglish
Article numberaa8364
JournalAstronomical Journal
Volume154
Issue number4
DOIs
Publication statusPublished - 2017 Oct

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metallicity
spectroscopy
stars
metal
Hydra
chemical evolution
spectroscopic analysis
metal clusters
globular clusters
metals
spectrographs
observatories
observatory
optical fibers
telescopes
trends
gradients
fibers
high resolution
estimates

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

An, D., Lee, Y. S., Jung, J. I., Rey, S. C., Rhee, J., Lee, J. W., ... Joe, Y. H. (2017). Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri. Astronomical Journal, 154(4), [aa8364]. https://doi.org/10.3847/1538-3881/aa8364
An, Deokkeun ; Lee, Young Sun ; Jung, Jae In ; Rey, Soo Chang ; Rhee, Jaehyon ; Lee, Jae Woo ; Lee, Young Wook ; Joe, Young Hoon. / Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri. In: Astronomical Journal. 2017 ; Vol. 154, No. 4.
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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 .",
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An, D, Lee, YS, Jung, JI, Rey, SC, Rhee, J, Lee, JW, Lee, YW & Joe, YH 2017, 'Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri', Astronomical Journal, vol. 154, no. 4, aa8364. https://doi.org/10.3847/1538-3881/aa8364

Medium-resolution Spectroscopy of Red Giant Branch Stars in ω Centauri. / An, Deokkeun; Lee, Young Sun; Jung, Jae In; Rey, Soo Chang; Rhee, Jaehyon; Lee, Jae Woo; Lee, Young Wook; Joe, Young Hoon.

In: Astronomical Journal, Vol. 154, No. 4, aa8364, 10.2017.

Research output: Contribution to journalArticle

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AU - Rey, Soo Chang

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