PoS(NIC-IX)062 C 13 http://pos.sissa.it/ ) and different  Fe. 60 ∗ Al and 26 [email protected] [email protected] [email protected] [email protected] [email protected] . For each we followend the evolution of from the the Thermally Pre Pulsing Main AGB Sequencevelocities Phase. up at to the By the means inner of border an of exponential the decay convective of envelope the we convective obtain the formation of a tiny pocket after Third Dredge Up episodes, whoseDetailed pulse extension by in pulse mass surface enrichments decreases and along final yields theusing at AGB a different metallicities, path. full computed nuclear by network coupled todiscussed. the FRANEC We stellar follow evolutionary the code, production are of presentedresponsible and both for light and their heavy production elements and describingsuch show nuclear as chains new results for the synthesis of radioactive isotopes Speaker. We present a new set of low mass AGB models having the same mass (2 M ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c International Symposium on Nuclear Astrophysics —June Nuclei 25-30 in 2006 the Cosmos — IX CERN, Geneva, Switzerland Inma Dominguéz Universidad de Granada E-mail: Universitá degli studi di Torino, Dipartimento diE-mail: Fisica Generale Luciano Piersanti Osservatorio Astronomico di Teramo (INAF) E-mail: Oscar Straniero Osservatorio Astronomico di Teramo (INAF) E-mail: Roberto Gallino Sergio Cristallo Osservatorio Astronomico di Teramo (INAF) E-mail: Light and heavy elements nucleosynthesis inmass low AGB  PoS(NIC-IX)062 56) ≥ O reaction. 16 ), representa- 4 Sergio Cristallo − ,n) α 10 × C( C pocket, presents a 13 N has been previoulsy 13 =1 Z 14 4) [1]. In this phase, the < N (a strong neutron poison) and  C and subsequently, when the 14 , assumed as representative of   13 Z C. Then, an alternative source of ) M 13 ν 2 ≡ M/M + C pocket. This pocket can form if, at 2 = β − 13  M 10 N( × 13 ) γ =1.5 Z O reaction is efficiently activated in the pocket, C(p, 2 16 12 ,n) α C( 13 captures. Later on, when this region heats up again, protons are N is depleted: the so-called K, the α ) and is believed to occur during the explosive phases at the end of 14 8 3 at different chemical compositions: these models have been obtained − C via the sequence  12 cm M 20 =2 C left in the H-shell ashes produces a negligible neutron exposure: this is due 10 M 13  n n Ne by means of 22 We compute two models with the same initial mass ( The abundances in the are due to the mixing of material ejected from stars that C and s process elements. In AGB stars, the main neutron source is the C is needed, in a zone where captured by the abundant 2. The models 13 12 Light and heavy elements nucleosynthesis in low mass AGB Stars 1. Introduction are created by means of neutrontron capture densities processes: ( by the r process, which requires very high neu- polluted the interstellar matter before the formation of the . Isotopes heavier than iron (A to the fact that, in the material processed by the CNO burning, the by including into the FRANECat stellar the evolutionary termination code point a of the fulloretical s nuclear cross process network path), sections. (from upgraded H The with the upthe predicted most to AGB modifications recent Bi, evolution of experimental and the are the- surface shownwith compositions Galactic in s occurring Section process during 3. enriched stars. Moreover, Finally, in we Section compare 4 our we report theoretical our distributions conclusions. the evolution of massive stars,totic and Giant by Branch the (TP-AGB) s phase process, of active low during mass the stars Thermally (1.5 Pulsing Asymp- producing a large amount ofing neutrons protons which into are captured a by thin the layer iron of seeds. the The He-intershell, problem to of produce mix- the so-called the moment of the maximum penetrationamount of of the protons convective envelope are during injected TDU into episodes, the a radiative small He-intershell, where the low mass AGB stars) with different metallicities ( temperature reaches about 10 is, in any case, two orders of more abundant than the consists of aH partially shell degenerate by carbon-oxygen a core, small ato He-rich He balance region shell the (He-intershell), separated surface and from irradiation a a isinner convective mainly envelope. border provided The of by energy the the required convective Hclear burning envelope. runaway shell, This (Thermal located situation just Pulse, belowbecomes is TP) the unstable recurrently in to interrupted the convection for by He-shell; a aing short as temporarily thermonu- period, a dies the consequence down. external layers After ofHe-intershell expand this a (Third and episode, Dredge the TP, the the H Up convective shell episode, He-intershell envelope burn- TDU), can carrying penetrate out in to the the C-rich surface the freshly synthesized converted to challenge in stellar modelling: weconvective attack velocities it at by the introducing inner an bordertions exponentially of decaying of the profile a convective of star envelope. the with In Sec. 2 we report computa- tive of galactic disk and haloof stars, respectively. these For models a detailed we description refer of to the physical [2, evolution 3]: here we concentrate on the chemical evolution. With respect The burning of the PoS(NIC-IX)062 . 6) elements 2 ≥ Sergio Cristallo Z C-pocket decreases F reaction, while the 13 ; 19 ) ] γ ) 2 , ) 4 . P α 0 ( ; log ( N = · C pocket. This pocket partially ) 15 4 13 η . Na pocket, which originates from 282 ( . 0 23 2 eff 10 3 2 T · = , the final distributions corresponding − L 1 P M η · ( log · 2 η eff 3 2 · T 26 · . L 5 M 63 − · + 6 . 10 η · 3 × 5 101 − − . [ 34 . 5 10 . The label El stands for the generic element. 10 1 −  × for the entire AGB evolution, respectively. This has been ⎧ ⎨ ⎩ 10 4 C-rich layer: the so-called 34 . This procedure guarantees an accurate determination of the . − (Fe)) O reaction, with the exception of the first pocket of the solar × 13 1 Y N max 5 16 10 Ne (see [6]). The extension in mass of the = = = × ,n) 22 (El)/ and ú -burning during the TPs and is mixed with the envelope by TDU ú ú 1 M α N M M Z α = C( C burns completely in radiative conditions during the interpulse phase, log( Z 13 1 − 13 . N pocket, followed by a further minor 3 14 ≤ (Fe)) N 5 1 P . . 2 3 log (El)/ < > N ≤ P P 5 . refer to models computed by interpolating the opacity coefficients with the metallicity or test for log for log for 2 http://www.oa-teramo.inaf.it/osservatorio/personale/cristallo/data_online.html . [El/Fe]=log( In Table 1 we report, in the usual spectroscopic notation Concerning the solar metallicity model, light elements are mildly enhanced: while C is the 2 1 • • • and episodes, the surface nitrogen enrichmentsized is in totally the convective due shell to generated the by first the dredge TP up. by means Fluorine of is the synthe- remains almost unchanged.TDU However, episodes AGB (mainly envelopes at become lowof metallicities), largely which the enriched has opacity in strong coefficients consequences carbonthe (we for after second the refer point, determination to we Sectionanalysing derive 3 a a sample for theoretical of the mass Galactic analysis loss C-rich and rate of O-rich as this AGB stars a problem). (see function [4, of Concerning 2] the and references pulsation therein): period, by 3. Nucleosynthesis results Light and heavy elements nucleosynthesis in low mass AGB Stars to previous versions of theopacity stellar code coefficients (see has [3] been andity introduced references changes, therein) and caused a a different by new treatment theconvective mass of variation mixing loss the of and rate microscopic the diffusion, internal has arebetween chemical been now tables composition adopted. taken with due into different to The account nuclear bysurface opac- linearly burning, abundance interpolating variations, provided that the relative distribution of the heavy ( releasing neutrons via the metallicity model (see next Section). done in order to explorerespect the to sensitivity the of adopted thethree opacity physical models; treatment. and an chemical extended In electronic evolution Table version of 2 of the we Tables model 1 report and with the 2 is total available cumulative on yields the of web the The introduction of a physical algorithm for[5, the 3]) treatment allows of the the partial convective/radiative interfaces diffusionto (see the of subsequent protons formation in of the a top tiny layers of the He shell, giving naturally rise by using opacity tables at to the solar metallicity case (columnst 2) and to the low metallicity case (columns 3 and 4): the label proton captures on the abundant overlaps with an outer along the AGB path. The main product of the partial 3 PoS(NIC-IX)062 C 13 .  M Sergio Cristallo model (column 2)  Z = [8], which is character- test Z 2 test 4 − − 4 1.3 case of [7]: the average − 10 × 10 × 10 × × 1 =2 C pocket is artificially introduced. 1 Z = 13 = Z Ne, active during the formation of the Z 22 st st 4 − 4 − model with label refers to a model computed by interpolating in 10  10 st × 4 M × 1 2 1 = one to a model where the opacity coefficients are calculated = = Z M =0.5. By varying the efficiency of the parameterized Z test η  Z  Z = = Z 8.1E-01 1.1E+00 2.3E+00 1.7E-01 1.0E+00 2.8E+00 5.3E-01 2.6E+00 3.1E+00 5.6E-013.0E-01 2.6E+002.1E-03 6.4E-01 7.4E-01 3.3E+00 1.5E+00 1.3E+00 4.9E-01 2.4E+00 3.7E+00 1.1E+00 6.4E-01 1.7E+00 Z ] ] ] ] ] ] ] ] Fe Fe Fe Fe Fe / Fe Fe NO 1.4E-03F -1.0E-04Na 2.6E-05 9.3E-07 2.1E-05Al 2.1E-04Fe 3.9E-07 7.8E-07 2.7E-06 1.1E-07 1.2E-04 1.4E-08 6.6E-04 6.7E-09 1.2E-05 1.2E-04 2.6E-07 2.2E-08 C 6.0E-03 7.9E-03 3.1E-02 / Fe / / / / / / model (column 3 and 4). The 14 16 19 23 26 60 12 4 C N O F Na ls hs Pb [ [ [ [ [ [ [ [ − 10 As in Table 1, but referring to cumulative yields. All tabulated values are in × 1 = Z Final surface overabundances (in the usual spectroscopic notation) for the Table 2: Na pocket (see previous Section). All heavy elements (from Sr to Pb) are enhanced: we find and for the 23 low Na enhancement is mainly due to proton capture on Table 1: Light and heavy elements nucleosynthesis in low mass AGB Stars that the abundance of the so-calledelements (Ba, ls La, elements Ce, (Sr, Pr, Y Nd). andstars Zr) of is is this underproduced metallicity. comparable with We with compare respect the our toa surface one barium, post-process enrichment of as technique distribution expected the with [7], for hs the AGB where one a obtained constant with pulse by pulse This calculation has been performed on a with a fixed (the initial one) metallicity. metallicity the opacity coefficients, while the ized by a Reimers’ mass-loss rate with pocket, we find that ourenhancement model is of approximately s equivalent process to elementspletely the is ST different roughly evolutions the along same, even thewhile if AGB the the phase. post-process distributions calculation We result in runs from[8]. fact over com- However, a obtain we model recall 11 characterized that pulses the by followed introductionefficient 22 by of with pulses the TDU, respect followed velocity by to profile TDU algorithm previousof makes calculations: our TDU TDU episodes, this more which feature is counterbalances mainly the determined decreased by number the adopted mass-loss rate. In order to evaluate PoS(NIC-IX)062 )  5 M − 3 10 ), who = × 2 M . case: at the Mg reaction model is en- 25 Sergio Cristallo test  Z Fe)=6 ,n) 1.6), producing a 56 α = ( O is of primary ori- ∼ X Z 16 8 Ne( T 2.3) with respect to the these proceedings case as compared to the ,n) 22 Mg reaction. We there- ∼ Fe)/ Al is efficiently produced α 26 60 26 ( test C( X Pb, at the termination point of 13 208 Al(n,p) 26 Mn production (see [10]). Useful hints case), which has strong consequences on 53 test C burning. This fact has minor consequences Al (the final surface aluminum isotopic ratio is 13 5 26 C burns at higher temperatures ( C burning is taken into account (see [10]). Even if we 13 case as our best model at low metallicity. As expected at case) to 49 ( 13 Fe production is instead mainly due to a single convective case. The observed level is attained by our 60 C pocket is engulfed by the convective shell generated by the st st 13 test Fe surface abundance is increased ( Fe belong to this class. The surface of our 60 Al as a consequence of TDU episodes ( ). The 60 26 3 − C pockets. Theories claiming that a Type II was the unique Al is only weakly destroyed by the 10 Mg in the H-burning shell). In fact, the temperatures attained at the bot- 13 26 × 25 Al and 3 . 26 Fe, we can’t claim that an AGB star has been the unique polluter of the Early So- Al))=5 , with NO 60 27  ( Fe in a deep-sea ferromanganese crust, compatible with the deposition of ejecta from a Z X 1 3 60 pulse with TDU. The value we find lies in the range spanned by observational data. = th Other interesting by-products of AGB nucleosynthesis are the short-lived isotopes, whose role Concerning the low metallicity cases, the data in Tables 1 and 2 clearly indicate how the opac- Al))/ Z 26 case. Note that the choice of a lower mass loss rate should increase the number of TPs as well, C burning episode, when the first ( and 13 Light and heavy elements nucleosynthesis in low mass AGB Stars the efficiency of the adopteda velocity sample profile of algorithm, solar we compare metallicitysurface our galactic ratios surface C(N) are [hs/ls] Giants about value [9] with 1, (leftthe we panel 6 report of our Fig. envelope 1): composition since for their C/O=1, mean which C/O is attained after is of primary importance in theSolar determination System of [10]: the astrophysical source which polluted the Early moment, we therefore assume thethese metallicities, we findepisodes, a and strong a carbon large enhancement lead overabundance ([C/Fe]=3.3), ([Pb/Fe]=3.1). consequence While of the the TDU ity treatment affects the model evolutionthe (for pulse a detailed number analysis increases see Sectionthe from 8 chemical 9 of surface ( [2]). enrichment: In particular, st it appears largely enhancedallowing in the the model to reachbest larger model surface comes overabundances. from A spectroscopic[11]): useful measurements the guideline of majority in low of identifying metallicity thesetheoretical the halo stars expectation stars show found (see larger in [hs/Fe] Table the 1 values in (up to with nearby SN. lar System (ESS), because ofsolve a this too problem, large palladium [10] production postulated (see that discussion the in ESS [6]): was in polluted order from to an AGB star with tom of the convective TPs are not high enough to efficiently activate the polluter of the ESS are instead dealing with a too large following TP (see [6]). In this case the obtain more X on the physical and chemicalisotopes; evolution accordingly, of our final the star, except for the nucleosynthesis of neutron-rich on this debated argument could come from the work of Korschinek et al. ( detected the s process [12]. Theof large the carbon increased and number fluorine surface of enrichments TDU are episodes, the while direct the consequences final nitrogen increase is instead due to the by proton captures on fore find a substantial surface enhancement of larger neutron density with respect to a radiative gin, the iron seeds scale withlow metallicity, metallicities, resulting most in of a the seeds larger number are consequently of neutrons converted to per iron seed. At riched of freshly synthesized and, consequently, the with respect models where a standard PoS(NIC-IX)062 test these pro- C pocket, 13 Sergio Cristallo case) seems to overstimate the atomic st : theoretical expectations (blue solid line: Na pocket, and during the convective TPs, where 6 Right Panel 23 C pocket allows us to evaluate the s process surface en- . Note that a dilution factor is required for both theoretical 13 4 − 10 × 2 Mg reaction (see also the contribution from Gallino et al., = 25 Ne give rise to a tiny Z 22 ,n) Ne in the He-intershell captures a fraction of the neutrons released by the α 22 : observed [hs/ls] ratio of a sample of galactic C(N) Giants [9] (blue circles), com- Ne( N). Sodium production occurs at the epoch of the formation of the star with 22 14  M 5 . Left Panel 1 ). In the right panel of Fig. 1 we compare our theoretical expectation (solid blue curve) = The self-consistent formation of a M Figure 1: pared with our theoretical prediction (red triangle); FRANEC [this work]; red dottedand line: HD post-process 201626 calculation [13]. [12]) compared with spectroscopic data of 4. Conclusions mixing with the envelope, duringare TDU enriched episodes, in of the H shell and the underlying layers (which Light and heavy elements nucleosynthesis in low mass AGB Stars activation of the ceedings with spectroscopic measurements of the leadthe star curve HD obtained 201626 with [13]; in theof the post-process a same calculation Figure [12] we also (red plot dotted line), relative to a ST/3 case curves: this implies that this stardetermined is the an orbital extrinsic elements AGB of star, the in system agreement to with which the this work of star [14], is who belonging. richment of low mass AGBWe found stars a and good to agreement compare withreproduce it observations the with at abundances the both spread, extant metallicities,abundances observed even spectroscopic seem if at measurements. to a low suggest single metallicities that modelcase) the [12]. cannot is model more efficient The computed in with resulting reproducing opacity spectroscopicthe final data metal tables surface at enrichment at low of metallicities, fixed the while metallicity envelope the iscontribution ( model taken where to into account the ( opacity.contribution This to discrepancy opacity, turns which our has attention been to demonstrated the to problem be of dominant the in the molecular external layers of the the abundant primary when proton captures on PoS(NIC-IX)062 , 774. Sergio Cristallo 77 case is a conse- st ,5. 777 Mem. SAIt , 700. 75 , 389. , 1159. 20 554 , 311. , 291. Nucl. Phys. A ApJ PASA 777 , 239. Mem. SAIt 404 37 , 217. , 709. A&A 688 , 352 ARA&A 7 Nucl. Phys. A ApJ , 388. , 817. 497 579 Nucl. Phys. A ApJ ApJ , 507. , 118, 1363. 387 PASP A&A Moreover, it has to be stressed that the low number of thermal pulses in the [2] Cristallo, S.: 2006, [3] Chieffi, A., Domínguez, I., Limongi, M., Straniero, O.: 2001, [4] Straniero, O., Gallino, R., Cristallo, S.:[5] 2006, Cristallo, S., and 6 coauthors: 2001, [6] Cristallo, S., Gallino. R., Straniero, O., Piersanti, L., Domínguez, I.: 2006, [7] Gallino, R., and 7 coauthors.: 1998, [8] Straniero, O., Domínguez, I., Cristallo, S., Gallino, R.: 2003, [9] Abia, C., and 8 coauthors: 2002, [1] Busso, M., Gallino, R., Wasserburg, G. J.: 1999, [10] Wasserburg, J.J., Busso, M., Gallino, R., Nollett, K.M.: 2006, References Light and heavy elements nucleosynthesis in low mass AGB Stars cool AGB envelopes when thefuture C/O works. ratio is bigger than 1 (see [15]):quence not we only deserve of this the opacityrate. analysis coefficients to treatment, The but large it dependstheoretical scatter also fitting in on curve: the the adopted it observational mass-loss mass-loss is data on therefore the cannot necessary number obviously to of investigate termal bequences the pulses on reproduced by effect the using means of following a chemical reducing a new evolution. the set single adopted of models and to evaluate the conse- [15] Marigo, P.: 2002, [11] Bisterzo, S., and 5 coauthors: 2006,[12] OMEG05 Symposium, Gallino, in R., press. Arnone, E., Pignatari, M.,[13] Straniero, O.: Van 2005, Eck, S., Goriely, S., Jorissen, A.,[14] Plez, B.: McClure, 2003, R.D., & Woodsworth, A.W.: 1990,