Durham Conference New Era in Cosmology

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Stellar Abundance Anomalies Always nucleosyn
thetic? David L. Lambert Director, The W. J
. McDonald Observatory The University of Texas at
Austin
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A NARROW HYPOTHESIS

• The composition of a stellar atmosphere is
• exactly that of the natal interstellar cloud
• Demonstrably fails for many stars
• Often, multiple causes behind the failure
• .FORTUNATELY!

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FAILURE MODES

• Nucleosynthesis
• dredge-up, mass loss, surface nuclear reactions,
  astration
  
• binary stars mass transfer, mergers
• Diffusion
• radiative levitation vs. gravitational settling
• Winds and fractionation
• dust-gas winnowing
• FIP effect
• Systematic errors

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Chemical homogeneity in the Hyades
Paulson et al. (2003)
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Chemical homogeneity in the Hyades
Paulson et al. (2003)
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Chemical homogeneity in the Hyades
Yong et al. (2004)
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M Dwarf binaries (Bean et al. 2006)

• Five binaries
• primaries from F7V to K3V
• secondaries from M0.5V to M3.5V

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DIFFUSION eclectic highlights

• Mercury manganese stars
• 3Cen A and 3He
• Isotopes of mercury
• Isotopes of calcium
• Lithium on the Spite plateau

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ISOTOPES OF MERCURY

• Hg greatly overabundant
• Wide range of isotopic mixes

Woolf Lambert (1999)
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BIG PICTURE?

• HgMn (and CP) stars
• no?
• Lithium in metal-poor stars
• yes?

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LITHIUM ON THE SPITE PLATEAU

• 7Li less than predicted from THE
• Big Bang by 0.3 dex
• Diffusion may be one way to reconcile
  observations and prediction, but consider
  
• Teff, g
• Granulation
• NLTE

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LITHIUM IN NGC 6397
Korn et al. (2006)
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R Coronae Borealis stars

• Very H-poor and He-rich
• Unpredictable declines
• Abundance as a means to test
• origins
• links to HdC (cooler) and EHe (hotter) stars
• Simple spectroscopic test?
• continuous opacity from photoionization of
  neutral carbon
  
• many excited lines of neutral carbon
• predict strength of C I lines independent of
  everything
  

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R Coronae Borealis stars

• Carbon problem C I lines weaker by 0.6 dex
• than predicted
• Solutions
• C I gf-values
• Continuous opacity not from C I
• NLTE for C I
• Non-classical model atmosphere

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R Coronae Borealis stars
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R Coronae Borealis stars
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H-DEFICIENT STARS HdC, RCrB, EHe

• Two production scenarios
• Final He-shell flash in a post-AGB star (FF)
• Merger of an He WD and a C-O WD (DD)
• Test via compositions
• 18O Clayton et al. (2005, 2007)

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HdC stars and OXYGEN-18

• 18O not produced in
• quantity by FF
• 18O may be produced in
• nucleosynthesis as the
• WDs merge

Starting and transforming discoveries
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HdC and RGB stars and OXYGEN-18
García-Hernández et al. (2007)
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DUST-GAS WINNOWING

• Signature Deficiency of elements of high
• condensation temperature
• ? Boo (Venn Lambert 1990)
• PAGB A-type spec. binaries
• (Van Winckel et al. 1995)
• RV Tau (Giridhar et al. 1992-2005)

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DUST-GAS WINNOWING

• Inefficient in
• cooler stars,
• Teff
• metal-poor stars,
• Fe/H -1
• Winnowing in
• stellar wind?
• accretion from
• circumbinary disk?

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First ionization potential effect?
DUST-GAS WINNOWING

• Signature of winnowing not always
• clear another cause?
• Solar corona and wind show FIP effect
• see EQ Cas

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DUST-GAS WINNOWING
Rao Reddy (2005)
Giridhar et al. (2005)
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DUST-GAS WINNOWING?
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POPULATION II CEPHEIDS - BL HER and W VIR
VARIABLES

• A Period-Luminosity sequence
• BL Her - P 5 days
• W Vir - 10 days
• RV Tau - 20 days

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POPULATION II CEPHEIDS - EVOLUTIONARY SCENARIO

• Evolution to the BHB
• requires mass loss
• and mixing of CN-cycle
• and 3a-process
• products
• Location on BHB
• related to Na-
• enrichment
• BL Her on BN track
• W Vir on D track

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POPULATION II CEPHEIDS - SPECTRA
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POPULATION II CEPHEIDS CHEMICAL COMPOSITIONS

• CNO spread with
• BL W RV indicating mix of CNO-
• cycle and 3a-process
• (R stars to weak G-band stars)
• BL Her are Na-rich proton-capture on 22Ne
• W Vir show hints of dust-gas winnowing

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POPULATION II CEPHEIDS
Na
Al
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Stellar Abundance Anomalies

• Always nucleosynthetic?