Barium stars: a subclass of extrinsic AGBs

1
Barium stars a subclass of extrinsic AGBs

• Laura Husti
• University of Torino
• Perugia 21-27 october 2007

2
Barium stars

• first reported by Bidelman Keenan 1951
  chemically peculiar G and K giants abnormally
  strong lines of BaII (4554 A) and SrII (4077 A,
  4215 A) and enhanced CH and CN bands
• abundance analysis - C and s-element
  overabundances (Burbidge Burbidge 1957, Warner
  1965, Smith 1984, )
• C and s-elements are formed in TP-AGB stars
• dwarfs and subgiants with same chemical
  composition peculiarities (Bond 1974, Tomkin et
  al.1989)
• much lower luminosities than stars on the TP-AGB
  (MacConnel et al. 1972, McClure 1973)
• MISTERY!

3

• Promising solution formation of barium stars in
  binary systems (McClure et al. 1980)
• Sustained by
• variations in radial velocity - binaries -
  companions with masses expected for white dwarfs
  (McClure 1983, McClure Woodsworth 1990)
• ultraviolet excess due to white dwarf companions
  (Böhm-Vitense 1980, 2000)
• Scenario Barium stars Extrinsic AGBs

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Mixing and Dilution

• extrinsic AGBs
• red giants first dredge up
• dwarfs thermohaline mixing

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How to choose the13C-pocket
Allen Barbuy 2006
6
HD 116869
Allen Barbuy 2006
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Dwarfs
Allen Barbuy 2006
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Intrinsic indicators
Allen Barbuy 2006
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Lead predictions
Smiljanic et al. 2007
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Conclusions

• comparison between theoretical models and
  spectroscopic observations for the element
  abundances of 30 barium stars
• studying the s process at about solar
  metallicities
• 13C-pocket range used for fits ST2 to ST/3
• AGB initial masses used for single fits 1.5 Mo,
  2 Mo and 3 Mo, same 13C-pocket, higher dilution
  factors for higher masses
• need for constrains on dilution factors