1. Is the 19 F 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)

2.  19 F 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)‏

3. ...Only AGB stars show observational evidence of 19 F 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)

4. Jorissen et al. (1992)‏ - 19 F abundances up to 30-50 solar - [F/O] vs. C/O correlation  production in TP-AGB stars C-richO-rich  M  MS  S  SC  C(N)

5. 19 F nuclear chain in He-burning conditions in TP-AGB stars: , 15 N, 18 O are needed: p & n from 14 N(n,p) 14 C and 13 C( ,n) 16 O 19 F has primary & secondary origins ( 13 C): at low metallicity primary source dominates  large [F/Fe] are expected Simultaneous 19 F & s-element production (?)

6. 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)‏

7. 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

8. 19 F 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

9. T eff = 3100 K, [Fe/H]= -0.4 C/O = 1.12, 12 C/ 13 C = 42 16 O/ 17 O =1240, 16 O/ 18 O =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 (C 2, CN, CO, CH) line lists - HF R9 line as the main F indicator (Gustafsson et al. 2008; Plez et al. 2008)

10. T eff = 2800 K, [Fe/H] = 0.0 C/O = 1.17, 12 C/ 13 C = 52 16 O/ 17 O = 1200 [F/Fe] = 0.10 ± 0.05 [F/O] = 0.22 AQ Sgr

11. T eff = 2825 K, log g = 0.0, [Fe/H]= +0.06 C/O = 1.06, 12 C/ 13 C = 50, 16 O/ 17 O = 1125, 16 O/ 18 O = 1150 [F/Fe] = 0.26  0.04 [F/O] = 0.2 UU Aur

12. Main Results Mean difference in 32 stars re-analysed  [F/Fe]= +0.6 In some stars differences up to 1 dex ! Unable to derive 19 F abundances for Mira variables (JSL did !) J-type stars show no 19 F enhancements SC-type stars show the largests 19 F enhancements (but no so large)

13. Why..? Stellar atmosphere parameters....±0.2 dex, no! Atomic line parameters...no! Atmosphere models.... +0.1 dex Molecular blends C 2, CN, CH.....very probably ! log  ( 19 F) = 4.88 ± 0.04log  ( 19 F) = 5.65 (JSL) Wavelength (Å) UU Aur

14. T eff = 2800 K, [Fe/H] = 0.0 C/O = 1.01, 12 C/ 13 C = 4.5 16 O/ 17 O = 450, 16 O/ 18 O = 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 19 F abundance in agreement with the JSL analysis

15. C(N)-stars SC-stars J stars    1.5, 2, 3 M  TP-AGB Z=0.006 FRANEC code  19 F vs. s-elements

16. JSL

18. C(N)-stars SC-stars J stars M, MS, S stars 1.5, 2, 3 M  TP-AGB Z=0.006 FRANEC code      11 th

19. 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

20. The [F/Fe] vs. C/O correlation dissapears...for C/O > 1!!  2 M , Z=0.008 FRANEC code 

21. Summary Extra-mixing and/or changes in reaction rates seems not necessary to explain 19 F abundances in AGB C-stars. 19 F and s-element enhancements are correlated in intri. AGB stars. Yet there is a problem in explaining 19 F, s-element abundances and the C/O ratios simultaneously in AGB C-stars. SC-stars... are they in the sequence M  MS  S  SC  C ? 19 F & s-element determinations in low [Fe/H] AGB C-stars needed to evaluate the yield from AGBs and test nucleosynthesis models!!!