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)

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)

...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)

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)

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 (?)

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)

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

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

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)

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

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

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)

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

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

C(N)-stars SC-stars J stars

1.5, 2, 3 M TP-AGB Z=0.006

FRANEC code

19F vs. s-elements

JSL

JSL

C(N)-stars SC-stars J stars M, MS, S stars

1.5, 2, 3 M TP-AGB Z=0.006

FRANEC code

11th

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

The [F/Fe] vs. C/O correlation dissapears...for C/O > 1!!

2 M, Z=0.008 FRANEC code

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!!!