Download - Is the 19 F problem in AGB C-stars solved ?
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Is the 19F problem in AGB C-stars solved ?
C. Abia (UGR)S. Cristallo (UGR-INAF)K. Cunha (ORJ)P. de Laverny (OCA)I. Domínguez (UGR)K. Eriksson (Upssala)L. Gialanella (Napples)K. Hinkle (NOAO)G. Imbriani (Napples)A. Recio-Blanco (OCA)V. Smith (NOAO)O. Straniero (OACT-INAF)
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19F is a fragile element easily destroyed by p & captures and difficult to observe in astrophysical objects.
Its origin is not very well known...
-induced spallation in SN II (Woosley et al. 1990)
TP-AGB stars (Forestini et al. 1992)
Hydrostatic He-burning in heavy mass-losing WR (Meynet & Arnould 2000)
Chemical evolution models suggest the contribution of all the three sources (Renda et al. 2004)
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...Only AGB stars show observational evidence of 19F production, (Jorissen et al. 1992) confirmed by observations in post-AGB stars and planetary nebulae (Werner et al. 2005; Zhang & Liu 2005; Otsuka et al. 2008)
Renda et al. (2004)
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Jorissen et al. (1992)
- 19F abundances up to 30-50 solar - [F/O] vs. C/O correlation production in TP-AGB stars
C-richO-rich
MMSSSCC(N)
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19F nuclear chain in He-burning conditions in TP-AGB stars:
, 15N, 18O are needed: p & n from 14N(n,p)14C and 13C(,n)16O
19F has primary & secondary origins (13C): at low metallicity primary source dominates large [F/Fe] are expected
Simultaneous 19F & s-element production (?)
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3 M TP-AGB, Z = 0.02 Lugaro et al. (2004)
Models and observations mainly disagree in AGB C-stars
1.5 M TP-AGB, Z = 0.018 Goriely & Mowlavi (2000)
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1.5, 2 M, Z=0.006 TP-AGB FRANEC code
...After up-dated s-element abundances in AGB C-stars (Abia et al. 2002)
C-rich AGBs O-rich AGBs
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19F abundance determinations from rotational HF lines @ 2.3 m in intrinsic AGB C-stars
- Extragalactic C-stars as main targets (Magellanic Clouds, Draco, Carina, Ursa Minor, Sagittarius...)- Galactic field AGB C-stars as calibration objects- VLT & GEMINI, R ~ 50000
- Only one proposal accepted (after 4 trials !!!)- Only 3 galactic objects observed
We decided to re-analyse the Jorissen et al. (1992) FTS spectra
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Teff= 3100 K, [Fe/H]= -0.4
C/O = 1.12, 12C/13C = 4216O/17O =1240, 16O/18O =1450
[F/Fe] = 0.5 ± 0.1 [F/O] = 0.2
TX Psc
- Spec. synthesis with the state-of-the-art C-rich atmosphere models- Up-dated atomic and molecular (C2, CN, CO, CH) line lists- HF R9 line as the main F indicator (Gustafsson et al. 2008; Plez et al. 2008)
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Teff= 2800 K, [Fe/H] = 0.0 C/O = 1.17, 12C/13C = 52 16O/17O = 1200
[F/Fe] = 0.10 ± 0.05 [F/O] = 0.22
AQ Sgr
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Teff= 2825 K, log g = 0.0, [Fe/H]= +0.06
C/O = 1.06, 12C/13C = 50, 16O/17O = 1125, 16O/18O = 1150
[F/Fe] = 0.26 0.04[F/O] = 0.2
UU Aur
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Main Results
• Mean difference in 32 stars re-analysed [F/Fe]= +0.6
• In some stars differences up to 1 dex !
• Unable to derive 19F abundances for Mira variables (JSL did !)
• J-type stars show no 19F enhancements
• SC-type stars show the largests 19F enhancements (but no so large)
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Why ..? • Stellar atmosphere parameters....±0.2 dex, no!• Atomic line parameters...no!• Atmosphere models.... +0.1 dex• Molecular blends C2, CN, CH.....very probably !
log (19F) = 4.88 ± 0.04 log (19F) = 5.65 (JSL)
Wavelength (Å)
UU Aur
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Teff= 2800 K, [Fe/H] = 0.0 C/O = 1.01, 12C/13C = 4.516O/17O = 450, 16O/18O = 1600 log (Li) = 4.8
[F/Fe] = 1.15 0.18[F/O] = +0.80
WZ Cas
Evidence: SC-type stars have C/O 1
HF R9
19F abundance in agreement with the JSL analysis
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C(N)-stars SC-stars J stars
1.5, 2, 3 M TP-AGB Z=0.006
FRANEC code
19F vs. s-elements
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JSL
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JSL
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C(N)-stars SC-stars J stars M, MS, S stars
1.5, 2, 3 M TP-AGB Z=0.006
FRANEC code
11th
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C(N)-stars SC-stars M,MS,S stars
1.5, 2, 3 M TP-AGB Z=0.006
FRANEC code
Intrinsic AGB stars
C/O> 1
C/O> 1
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The [F/Fe] vs. C/O correlation dissapears...for C/O > 1!!
2 M, Z=0.008 FRANEC code
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Summary
• Extra-mixing and/or changes in reaction rates seems not necessary to explain 19F abundances in AGB C-stars.
• 19F and s-element enhancements are correlated in intri. AGB stars.
• Yet there is a problem in explaining 19F, s-element abundances and the C/O ratios simultaneously in AGB C-stars.
• SC-stars... are they in the sequence MMSSSCC ?
• 19F & s-element determinations in low [Fe/H] AGB C-stars needed to evaluate the yield from AGBs and test nucleosynthesis models!!!