47 Tuc sprocess abundance results from SALT

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47 Tuc s-process abundance results from SALT

• IXth Torino Workshop

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OUTLINE

• Globular clusters abundance anomalies
• 47 Tuc s-process element abundances
• Large Scale Survey the Robert Stobie
  Spectrograph (RSS) on SALT
• Synthetic line strength analysis
• 47 Tuc Spectra obtained using SALT

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• Therefore
• GC main sequence element abundances same as
  chemical composition of the initial gas cloud
• Evolved star abundances variations are evidence
  of types of nuclear processing and mixing

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Abundance anomalies in globular cluster stars

• Anticorrelation of CN to CH molecular band
  strengths
• Bimodal distribution of CN strength on RGB and MS
• Na-O ( Al-Mg) anticorrelation in RGB stars
• (Gratton et al 2004)

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MIXING (Cannon et al 1998) Dredge up
of processed material to the surface of the
star PRIMORDIAL Two gas clouds of differing
chemical composition merged prior to star
formation SELF-ENRICHMENT Previous generations
of cluster stars enriched the gas cloud either
through supernova or AGB stellar
winds POLLUTION Material ejected from AGB stars
in the cluster is accreted on to the surface of
the observed stars polluting their atmospheres
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Why are s-process element abundances useful?

• Enhancement of s-process elements occurs during
  the third dredge up in a thermally pulsing AGB
  star of mass gt 1M?
• Comparison of RGB stars with AGB stars tests
  nuclear product mixing theories
• Variations in s-process element abundances in
  both RGB and AGB stars is evidence for pollution
  by primordial scenarios (AGB ejecta)

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Globular Clusters s-process element abundances
Recent high resolution studies of several GCs
conclude no abundance anomalies for s-process
elements

• James et al 2004
• Uniform enrichment of s- r-process elements in
• NGC 6397 Fe/H -2.0
• NGC 6752 Fe/H -1.5
• 47 Tuc Fe/H -0.7

• Carretta et al 2007
• n-capture process elements are homogeneously
  distributed
• NGC 6388 Fe/H -0.44

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47 Tuc s-process element abundances

• Disagreement between studies of s-process
  element abundances in RGB stars in 47 Tuc

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47 Tuc s-process element abundances

• Wylie et al 2006
• Possible star-to-star scatter in s-process
  element abundances in 47 Tuc

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• High Resolution Medium Resolution
• Resolution ( ) 60,000 10,000
• Targets per Field 1-5 gt100
• Telescopes Instruments
• AAT UCLES AAOmega
• VLT UVES Flames (Rmax20,000)
• SALT HRS RSS

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Robert Stobie Spectrograph (RSS) Formerly the
Prime Focus Imaging Spectrograph (PFIS)
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What can RSS do?

• Maximum operating
• resolution 10,000
• Is this resolution sufficient to observe line
  strength variations in weak metal lines in GC
  stars?

47 Tuc CMD
SALT HRS
SALT RSS
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Synthetic line strength analysis of weak metal
lines
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High Medium Resolution Spectrum Synthesis of
Stellar Models
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High Medium Resolution Spectrum Synthesis of
Stellar Models
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Temperature Gravity Effects on the Giant Branch
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47 Tuc CMD
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Temperature Sensitivity
Zr I, Ba II not present Zr I, Ba II at model
abundance Zr I, Ba II enhanced by 0.5 dex Zr I,
Ba II enhanced by 1.0 dex
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Zr I Ba II
Zr I, Ba II not present Zr I, Ba II at model
abundance Zr I, Ba II enhanced by 0.5 dex Zr I,
Ba II enhanced by 1.0 dex
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Nd II Eu II
Nd ii Eu II not present Nd II, Eu II at model
abundance Nd II, Eu II enhanced by 0.5 dex Nd II,
Eu II enhanced by 1.0 dex
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Abundance Results
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Conclusion
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Future Work
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