Maximum Temperature in the He convective shell

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C-stars in Carina, Draco Ursa Minor satellite
galaxies
Carlos Abia Universidad de Granada
R. Wahlin (Uppsala) P. de Laverny (Nice) I.
Domínguez (Granada) S. Cristallo (Teramo) O.
Straniero (Teramo)
IX Torino Workshop on AGB stars 22- 27 Oct 2007,
Perugia
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The Vía Láctea neighbours
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Dwarf satellite galaxies

• They look like globular clustersbut they are
  not!
• CMD are complex several stellar populations
  (age, metallicity)
• SFR history not simple bursts, quiescent
  phases
• Building blocks of the Milky Way ? Origin of the
  galactic halo ?
• More than the closed box model. leaky box

• Existence of young and intermediate-age stellar
  populations

AGB (C)-stars of different initial metallicity
are accessible with 8 m class telescopes
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The s-process nucleosynthesis depends on the
metallicity
Dra
Car
Sag
UMi
SMC
? Travaglio et al. (2004)
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Metallicity distributions
Draco
Carina
Ursa Minor
-2
-1
0
Fe/H
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Observations
Carina dSph
- 2 C - stars (C6 C7), V ? 16 - 8 m VLT
UVES (R? 40000) and ISAAC (R?1500) - ?? ? 430 -
900 nm H K bands - S/N ? 40 - gt100 (UVES),
80 (ISAAC)
Ursa Minor

• 5 C - stars, V ? 17
• 4.2 m WHT ISIS (R ? 7000)
• ?? ? 640 - 810 nm
• - S/N ? 60

Draco dSph

• 3 C - stars, V ? 17
• 4.2 m WHT ISIS (R? 7000)
• ?? ? 640 - 810 nm
• - S/N ? 60

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Ursa Minor C-stars
CN C2
Ba II
?
H?
Fe I Ni I
?
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Draco C-stars
H?
Li I
Ba II
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Atmospheric parameters analysis

• Strong molecular contribution metal lines
  barely seen
• C,N,O abundances critical iteratively from CN,
  C2,CO (Carina)
• C-rich, metal-poor, spherical models from the
  Uppsalas group

• Teff vs. (V-K), (J-K), (H-K), ?Teff ? 100 K,
  Bergeat et al. (2001)
• Gravity from Mbol Teff
• ? 2 3 km/s, varies with ?
• Fe/H ?
• Iterative process necessary

Errors are large, ? X/H ? 0.3- 0.5 dex
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Examples of spectral syntheses
O from CO (ISAAC) K-band in ALW - C7
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N from CN (ISAAC) K-band in ALW - C7
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Metals s-process elements from UVES spectra in
ALW - C7
No s-elements
With s-elements
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Draco 20733, Teff 3800 K, Fe/H -2.0
La II
Ba II
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Evolutionary status ?
? R-hot ? R-cool ? N ? SC
AGB C-stars
?
?
?
?
?
?
?
?
?
?
CH stars
Carina Draco Ursa Minor
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Abundance results carbon enhancement
Carina, UMi, Draco
?
?
?
?
?
Normal C-stars
?
?
?
?
C/O1
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ALW - C6, Fe/H -1.7, ALW - C7, Fe/H
-1.9
Nd
?
?
Hf
?
Ba
?
?
?
?
?
?
La
?
Y
Sm
?
?
?
Ce
C
Zr
Sr
?
?
?
?
?
Rb
Ti
?
?
?
Zn
Mn
Ca
?
?
?
?
?
?
?
?
V
?
?
Ni
O
?
?
?
N
?
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from Ba La only
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2 M?, Z ? 10-4 TP-AGB
? Cristallo Domínguez 2007
C-enhancement is not well reproduced by
theoretical models
orextra-mixing (CBP), depletion,. ?
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Observations vs. s-process, Torino models
hs/Fe vs. Fe/H
?
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? courtesy R. Gallino
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ls/Fe vs. Fe/H
Carina stars only
?
?
?
?
? courtesy R. Gallino
?
?
?
?
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hs/ls vs. Fe/H
Carina stars only
?
?
?
?
? courtesy R. Gallino
?
?
?
?
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AGB model physics chemist fully coupled
2 M?, Z ? 10-4, 10th TP ? Cristallo, Straniero,
Domínguez 2007
C6 C7
Y, Zr
La, Ce
Zn
Hf
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Hint
depletion into dust grains in a C-rich
environment?
? courtesy K. Lodders
Ti seems also to be underabundant
in C7 !
AGB atmosphere
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Summary

• C/O ratios increase in C-stars as stellar
  metallicity drops ?

• s-element pattern agree with theoretical
  predictions M lt 2 M? ?

• Observed C/O 12C/13C difficult to reconcile
  simultaneously
• with
  stellar s-process AGB models ?

• Have we found extra-galactic (metal-poor!)
  R-stars ? ?

• Is there any depletion in ALW - C7 ? ?

Porchetta or Jamón?