14 N/ 15 N ratios in AGB C-stars and the origin of SiC grains Eurogenesis- Perugia Workshop, Nov 12-14, 2012 C. Abia R. Hedrosa (Granada) B. Plez (Montpellier) I. Domínguez (Granada) O. Straniero (Teramo) S. Cristallo (Teramo) S. Palmerini (Granada) Universidad de Granada

CW 0.6  m 10  m AGB stars: polluters of the ISM CW Leo  1 M  Detached shells: evidence of mass loss M  /yr > 50% of the mass (dust) injected into the ISM comes from AGB stars

Busso et al. (1999) 12 C M  MS  S  SC ?  N C/O ~  1... > 1 AGB chemical & spectral evolution

C/O < 1 C/O > 1 Effect on the spectrum Li I Ca I CN & C 2

The C/O ratio also determines types of condensates C/O < 1, oxides & silicates C/O>1, carbides, carbon, etc SiC grains

The giant C-stars Zoo Type Li s-process 12 C/ 13 C Remarks N no yes >40 SC some very few J yes no <15 15% 30% binary R-cool no yes >40 identical to N Zamora et al R-hot no low No AGBs, many are CH stars Zamora et al Thus, real AGB C-stars are N-, J- & and SC-type only

The Zoo of SiC grains & AGB C-stars © Davis (2011) standar AGB evolution extramixing allowed zone

Observations & Analysis ~ 40 Galactic C-stars of spectral types N, SC, J and R-hot 3.5 m TNG with SARG, R~170000, S/N > 300 Red System of the CN molecule ~ 8000 Å ( B. Plez) Atmosphere parameters (T eff, log g, [Fe/H],  ) from literature MARCS models for C-stars, 2 M  (Gustafsson et al. 2008) C/O ratio derived from 2.2  m spectra in a consistent way C 2 lines  C  CO lines  O  CN lines  N Iteration until convergence was reached !!

 Strong molecular contribution: metal lines barely seen  C,N,O abundances critical: iteratively from CN, C 2,CO (Carina)  C-rich, metal-poor, spherical models from the Uppsala’s group Errors are large,  [X/H]  ± dex  12 C 15 N were carefuly selected according to: - blending - sensitivity to the 14 N/ 15 N ratio - lines in the linear part of the curve-of-growth - uncertainty in the spectral continuum Only eight 12 C 15 N features selected in Å

LQ Cyg

Total formal error in 14 N/ 15 N is large: factor 3-5 (dispersion among 12 C 15 N, atmosphere parameters, CNO abundances, 12 C/ 13 C...)  Differential analysis line-by-line respect to TX Psc...this would reduce systematic errors (N-LTE effects, oscillator strenghts, continuum position etc.) For TX Psc we derived 14 N/ 15 N = nevertheless,  [ 14 N/ 15 N] TX Psc =  dex

 Testing our results with the expert code DEGAS Gaia & ESO-Gaia projects - DEGAS compares observed spectra with a huge grid of theoretical spectra, deriving stellar parameters & abundances (Kordopatis et al. 2011) - Three free parameters: 14 N/ 15 N, continuum position,   For 7 stars studied so far with DEGAS  ( 14 N/ 15 N) DEGAS- here = -29  230

Results ( 14 N/ 15 N) TX Psc = 1700

Comparison with SiC grains Open symbols are lower limits

Theoretical dependence on the initial 14 N/ 15 N ratio (no extramixing in RGB & AGB) 2 M , Z = 0.014, 14 N/ 15 N Wielen & Wilson (1997) ISM Initial FDU (1.5 M  ) (3.0 M  ) © FRANEC code Different initial masses might help to explain the observed 14 N/ 15 N range in N-type stars...

Variation along the AGB phase: s-elements 6 96 Mo is s-only & 92 Mo p-only 14 N/ 15 N appears not be afected by TDU episodes

Correlations with tracers of stellar interior: Li & F 18 O(p,  ) 15 N( ,  ) 19 F

SUMMARY We derive for the first time 14 N/ 15 N ratios in AGB C-stars 14 N/ 15 N appear to be different for different spectral types 14 N/ 15 N in N-type C-stars agree nicely with MS SiC grains First evidence of a contribution of J-type stars to AB grains SC-type stars might be enhanced in 15 N.... challenge for stellar evolution and nucleosynthesis !! Future  To extend the sample of C-stars with 14 N/ 15 N ratios  Study the 16 O/ 17 O/ 18 O ratios in the sample stars  Theoretical interpretation.....

Structure of an AGB star (1  M/M   8) CO H-rich He H shell burning He shell burning Convective envelope ~ 200 R 