“ The role of AGB stars in the early solar system chemical enrichment ”

1. “The role of AGB stars in the early solar system chemical enrichment” Heat, collisional processing, time Josep M. Trigo-Rodríguez Institute of Space Sciences (CSIC-IEEC) ATA, Llafranc, Apr. 4-6, 2011

2. OUTLINE The stellar environment in which our solar system formed Evidence in meteorites and cometary materials Stellar (presolar) products retained in primitive materials Short lived nuclides (SLNs) and stellar grains Components of carbonaceous chondrites: Astrophysical clues on the primeval solar system environment Volatile-rich chondrites AGB stars as sources of SLNs, stellar grains and organics: Nucleosynthesis products as function of stellar mass The 22Ne source to explain SLNs in CAIs Mainstream SiC grains from AGBs Additional sources: 81P/Wild 2 and IDPs from cometary bodies: D, C, and N clues Conclusions

3. THE METEORITICAL CONFIRMATION • Solar System formation took place from the gravitational collapse of a molecular cloud (Cameron, 1962): • Primordial and stellar nucleosynthetic heritage from meteorite components • Remote observation of proplyds (Herbig, 1977) plus theoretical studies (Lynden-Bell & Pringle, 1974) • First stellar grains in meteorites: a new age in laboratories (Bernatowicz et al., 1987) • Materials formed in stars found by chemical extraction (Anders, 1987; 1988) • Extreme isotopic anomalies • Secondary Ion Mass Spectrometer (SIMS) to get accurate isotopic abundances of components of meteorites (Ott, 1993; Bernatowicz & Zinner, 1997) NGC3603, adapted from HST image (NASA) NASA

4. STELLAR COMPONENTS Adapted from Lodders and Amari (2005) • The Sun and the protoplanetary disk formed in an environment rich in stellar products. • Growing evidence of the SS formation in a rich stellar cluster • A small part of the materials were not processed in the solar nebula, and are “presolar”: • Presolar (stellar) grains • Radioisotopes • In the components • Trapped in the matrix • Isotope anomalies • Principal sources: • Circumstellar shells of red giants • AGBs • SN and Novae ejecta • Here I will focus on the role of AGBs

5. STELLAR SOURCES: AGB STARS Asymptotic Giant Branch (AGBs): late stage of evolution of low- to intermediate-mass stars: 1  M  8 M TP phase: strong mass loss enriches the ISM with radionuclides and circumstellar dust grains! García-Hernández, 2005

6. AGB STELLAR NUCLEOSYNTHESIS • Thermal Pulsing phase  12C production, s-element production (Rb, Zr, Sr, Nd, Ba, Tc, etc.) • 3rd dredge-up very efficient in AGB stars; C/O ratio increases in the envelope (Straniero et al., 1995; Gallino et al., 1998) • Stars eventually turn C-rich and s-process rich following the M-, MS-, S-, SC-, C-type sequence unless… • Hot Bottom Burning (if M > 45M) • When Tbce 2×107 K  12C  13C, 14N (CN-cycle) and HBB prevents the carbon enrichment (stars remain O-rich) • 26Al, 7Li production, low 12C/13C & high 17O/16O ratios (Mazzitelli et al. 99; Karakas & Lattanzio 03 ) Late stage of massive AGB (García-Lario, unpublished)

7. THE s-PROCESS IN AGB STARS • Free neutrons to form heavier elements (s-elements such as Rb, Zr, Sr, etc.) can be released by 13C(,n) 16O or by 22Ne (,n)25Mg reactions (Straniero et al., 1995; Busso et al. 1999) • 13C operates during the interpulse period. It is more efficient in 13 M AGB stars. • All previous observations of AGB stars were consistent with 13C! • 22Ne is expected to be efficient in the convective thermal pulse at higher T and Nn. It should become strongly activated in more massive AGB stars (M>45 M). • This prediction was confirmed by accurately-reduced stellar spectra (García-Hernández et al., 2006, Science)

8. THE 22Ne NEUTRON SOURCE • The operation of the 22Ne neutron source favors the production of the stable isotope 87Rb (also of 60Fe, 41Ca, 96Zr, 25Mg, 26Mg, etc.) because of the operation of a branching in the s-process path at 85Kr (Beer & Macklin, 1989) García-Hernández, 2005

9. LOOKING FOR EVIDENCE IN FIRST MATERIALS...

10. CARBONACEOUS CHONDRITES • The most primitive rocks arrived to Earth • Rocks from water-rich bodies containing chondrules, inclusions and fine dust materials: • Until 10% H2O and 2 to 4% C in mass • Some CCs experienced aqueous alteration to different degrees (McSween, 1979) • Many mineral phases are aqueous alteration products (Zolensky & McSween, 1988): • phyllosilicates, sulfides, carbonates, and oxides • CCs chondrites suffered secondary processes after accretion (Brearley & Jones, 1998): • Aqueous alteration • Brecciation (consequence of impacts): amorphous C 1 cm window SEM image of Y791198 CM2 (Trigo-Rodríguez et al., 2006) Murchison CM2 chondrite

11. CIs and “SOLAR” COMPOSITION • Anders & Grevesse (1989) compared the chemical abundances measured in the solar photosphere with primitive meteorites (condrites) • Extraordinary fit with carbonaceous chondrites of CI group (meteorite-type: Ivuna) • In scientific literature is assumed that composition as “solar” since then • The CI chondrites are among the most fragile materials, but they have suffered important aqueous alteration • Genesis mission: chondrites have lower 16O content than the Sun (McKeegan et al., 2008) Solar vs. CI chondritic abundances Anders and Grevesse (1989) data Graph from Hutchison (2003) CI chondrite Orgueil (fell in 1864)

12. PRESOLAR COMPONENTS RETAINED IN PRIMITIVE CHONDRITES • Short-live radionuclides: • They were incorporated during condensation on mineral phases in the solar nebula: CAIs, chondrules, etc • A few (e.g. noble gases) were retained in the matrix during the early accretion of planetesimals • Stellar (also called presolar) grains • Fine-dust materials: • Carbonaceous materials with chemistry and isotopic anomalies inherited from the ISM, and stellar environment

13. CAIs: THE OLDEST SS MATERIALS • The Ca-Al rich Inclusions (CAIs) • The oldest materials: 45671 Myr (Amelin et al., 2002) • Formed by refractory minerals: spinel (MgAl2O4) + melilite (Ca2Al2SiO7)+ hibonite (CaAl12O19) • More accepted model: • CAIs are the resulting products of heating CI-composition dust clumps • CAIs retained a variety of isotopic anomalies (they are rich in 16O, 26Al, 53Mn, 41Ca, 87Rb) inherited from incompletely homogenized materials: • 60Fe excesses correlated with 96Zr  22Ne! (Quitté et al. 07) • It is a mere coincidence that CAIs show all the chemical anomalies expected in massive AGB stars? 0.5 mm-sized CAI surrounded by chondrules and matrix In ACFER 094 (Trigo-Rodríguez, unpublished) RGB X-Ray mapping (each color for Mg, Ca, Al) Note the relic aggregate-like structure

14. RADIONUCLIDES FOUND IN METEORITES • In particular short-lived nuclides (SLN) were important for planetesimals internal heating • They incorporated from the vapor phase into the minerals forming chondritic components

15. A MASSIVE AGB STAR IN THE ORIGIN OF THE SOLAR SYSTEM? • We have suggested that a 6.5 M AGB star of solar metallicity played a role in the Solar System enrichment in short-lived nuclides (SLN) • By comparing the SLN abundances in primitive meteorites with the isotopic pattern modeled for the surrounding environment of that AGB star • Our model match the abundances of 26Al, 41Ca, 60Fe, and 107Pd inferred to have been present in the solar nebula by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material • Such a polluting source does not overproduce 53Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements Image Gabriel Pérez Diaz (IAC) Publication details: Trigo-Rodríguez J.M., D.A. García-Hernández, M. Lugaro, A. I. Karakas, M. van Raai , P. García Lario, and A. Manchado (2009) Meteoritics and Planetary Science 44, 627.

16. refractory TYPES OF STELLAR GRAINS • Usually called “presolar” because: • These grains are suspicious to be formed in stellar outflows of late-type stars and in ejecta of stellar explosions • Their stellar origin is identified by their anomalous isotopic compositions compared to SS materials compiled from: Zinner, (2003) and Lodders and Amari (2005)

17. THE ORIGIN OF SiC GRAINS • The different groups reveal several stellar sources: • “Main stream” grains and groups Y, Z are from 1-4 solar masses AGBs (>90%) • Y-grains likely from intermediate-mass AGB stars: s-elements enrichments • A+B grains come from J-type stars of C • Or from Novae: 12C/13C<10 (José and Hernanz, 1998; José et al., 2001, 2004) Chemically extracted SiC grain (S. Amari) Courtesy L. Nittler

18. OXIGEN ISOTOPIC CLUES Wasson (2000) • Clayton et al. (1973) found that the O isotopic ratios are far from the line of Terrestrial fractionation (TF) • SMOW: standard mean ocean water • The drift from TF is measured by: • So the different planetesimals as a function of their formation region and instant of formation retained different isotopic abundances (Wasson, 1972) • Most carbonaceous chondrites (CCs) are falling into the CCAM (anhydrous minerals of CCs) • Some are outside that pattern being significantly altered by water: CM & CR • What is the origin of those anomalies? • A changing environment (stellar sources) • O-bearing molecules self shielding from UV NASA

19. A SCENARIO FOR iO ANOMALIES • Tielens & Heidenreich (1983) found that formation of O3 in gas phase produces mass independent isotopic enrichment: • A chemical mechanism for self shielding in the nebula • Subsequent analysis ruled out self-shielding of O2 (Navon & Wasserburg, 1985) • Lyons y Young (2005) supported again the origin of O anomalies as due to an irradiation process: • Nebular models (pH2=10-5 atm): half of the O was as CO and 1/3 as H2O • CO photodissociated by FUV (91 a 110 nm) • Predissociation energy specific for each isotope • Each CiO molecule will absorb FUV depending of their initial column densities • In the model: CxO+ h   C + xO (x=16,17 & 18) • 96 chemical species and 375 reactions • C17O and C18O species are more resistant to FUV flux • Inner disk is poor in 16O • Ices heritage of 17O & 18O higher abundances • 16O-enriched CAIs discovery (Clayton et al., 1973) • CCAM line with slope  0.9 • Pure 16O injected from nearby SN • Our 6Mo intermediate mass AGB model could also have enriched the outer disk in 17O and 18O-rich materials (Trigo-Rodríguez et al., 2009) • Before dilution with the nebula: 17O 4,500 Domínguez (2010), ApJ

20. PHOTOCHEMISTRY IN CIRCUMSTELLAR ENVIRONMENTS • We are just starting to understand the photochemical processing experienced by stellar products in AGB circumstellar environments: • New Herschel telescope results! • If the solar nebula was subjected to enrichment from these stars, it likely had a key influence on the starting materials, mostly in the O isotopic composition • Objects formed in the outer disk should contain evidence Decin et al. (2010)

21. EVIDENCE FROM 81P/WILD 2 AND IDPs PET/NASA • 81P/Wild 2 particles decelerated in SiO2 aerogel from 6 km/s • A Jupiter Family Comet formed in the Kuiper Belt • In the Preliminary Examination Team we studied the mineralogy, chemical and isotopic composition of the surviving particles • Incoming particles were fragile aggregates • Fine grain materials rarely survived, but large mineral grains were almost intact • About a thousand with diameters of 5 to 300m

22. 81P/WILD 2-FORMING MATERIALS • The largest recovered grains in aerogel are ~5-15m in diameter: • The toughest fragments surviving capture were mainly olivine and pyroxene • Synthesized nearby the Sun: • Radial turbulence in the disk explains their presence (Bockelée-Morvan et al, 2002). • Fragile aggregates of relatively large mineral grains compacted in a fine-dust material similar to the matrix of carbonaceous chondrites • Fine-grained component is rich in organics and isotopic anomalies: • Detected enrichments in 15N/14N and D (Brownlee et al., 2006; McKeegan et al., 2006) 8 m-size particle (FEBO) (Brownlee et al., 2006) TEM image showing 15N hotspot (PET/NASA)

23. IDPs FROM 26P/GRIGG-SKJELLERUP • Formed in the outer disk and less processed by solar heat or impacts: • Comets preserved additional clues • Representative of “starting” materials • Porous cometary IDPs also preserve isotopic anomalies, particularly in N, H and O associated with the ISM • As expected, isotopic anomalies are not homogeneously distributed, but surrounding presolar grains Isotopic ratio images of IDP L2054 E1 (Nguyen et al., 2007) • Measured abundances in logarithmic scale of presolar silicates in CM and CM-like chondrites versus the aqueous alteration petrologic type Trigo-Rodríguez & Blum (2009), PASA

24. CONCLUSIONS • Materials preserved in primitive meteorites and comets provide information on protoplanetary disk forming components: • Evidence of condensates from SN explosions and AGB and Novae stellar outflows • AGB stars played a key role in the chemical enrichment of the solar nebula • Observed radionuclides in CAIs are identical to the expected for intermediate-mass AGBs • SiC grains are typically associated with AGB low mass stars. • Why are intermediate-mass AGB condensates apparently missing? • Recent evidence in 81P/Wild 2 materials and cometary IDPs: • Importance of turbulence and mixing in the early protoplanetary disk • Astrophysical models for the formation conditions of CAIs, chondrules, presolar grains should be revisited • Cometary matter as source of additional information: • Lower degrees of thermal and aqueous alteration than primitive chondrites • Importance of recovery of “pristine” materials in future sample-return missions: • Marco Polo-R presented to last call of Cosmic Vision • Cryogenic mission to a comet proposed to NASA (Sandford et al., 2010) Thanks to A. García Hernández, M. Lugaro & L. Nittler and… to all of you!

25. A workshop to get clues on the earliest setting and evolution of planetary atmospheres: Works dealing with accretion, differentiation, outgassing, impacts, and energy fluxes from their host stars are welcome N is a biogenic element and its delicate balance with O in the Earth’s atmosphere conditions the habitability of the surface You are kindly invited to attend! Note that the workshop is scheduled during the days of famous La Mercé party in Barcelona: 21-23 Sept. 2011

26. S. Amari (2009) GRAPHITE GRAINS • We don’t know yet the number of stars required to explain the different groups of graphite grains • KE3 and KFA1 from SNe • KFC1 from low metallicity AGB stars • A few from Novae • Nanometric-sized grains: • Low abundance of trace elements makes difficult the study of isotopic anomalies • Out of equilibrium processes in circumstellar environments of massive AGB could be the origin of some of them • Accurate models needed • Clues in studies of trace elements • Better analytical techniques!

27. CARBON-RICH SOURCES: COMETS Data compilation by Morse et al. 2009 • Fragile bodies are not surviving atmospheric entry due to their low tensile strength, and high porosity (Trigo-Rodriguez & Blum, 2010) • The outer disk was rich in organic material containing ISM signatures • Remote evidence obtained from comets’ spectra with 12C/13C ratios close to terrestrial • Recent discovery of ultracarbonaceous micrometeorites (Duprat et al., Science, 2010) C/1996 B2 Hyakutake NanoSIMS-50 isotopic and elemental map of an ultracarbonaceous micrometeorite found in Antarctica. From Duprat et al. (2010)

28. MAINSTREAM SiC GRAINS (>90%) Carbon isotopes match AGB stars, 13C rich and 15N-poor from dredge-up of CNO cycle Infrared emission feature from SiC in AGB star (Speck et al, 1999) Most SiC grains formed in AGB stars! final stage of low-mass (<8MO) stars

29. DATING SYSTEMS BASED ON PRIMORDIAL RADIONUCLIDES • Two types of isotopic system are used to determine timing of events in the solar nebula • The quantity of a stable daughter isotope derived from the decay of a proportion of an extant long-lived radioisotope gives the absolute age or time to the present since the system became closed to isotopic interchange • Also the quantity of an isotope inferred to have been produced by the total decay of a short-lived isotope yields the period between isotopic closure, and the time when the parent became extinct • Both systems are cross-calibrated with precise U-Pb ages of rapidly cooled igneous meteorites * T1/2=0.693/, being  the decay constant