Presolar grains in meteorites: Isotopic signatures and timescales earthly stellar celestial the focus on isotopes facts speculations U. Ott Bern, April 14,2010
STARDUST grains in meteorites carbonacoeus chondrites constituents: -- chondrules -- Ca-Al-inclusions (CAIs) - matrix (w/ stardust) silicon carbide (SiC) mostly solid (facts) often speculative diamond (C)
Outline earthly history discovery story the inventory stellar history forward age (timescales of nucleosynthesis, grain formation) celestial history backward age ( absolute age )
Earthly History.began in about 1964: Reynolds and Turner: stepwise release and analysis of xenon isotopes in carbonaceous chondrite Renazzo Allende meteorite: Xe released in certain temperature steps: up to ~2x relative enhancement of lightest and heaviest isotopes Xe-HL from presolar diamond 124 Xe/ 130 Xe [ ] own similar historical analysis (1978): Allende DI #2 136 Xe/ 130 Xe [ ]
similarly, heat a primitive CM / CI meteorite, in certain temperature steps: enhancement of 22 Ne Maribo CM chondrite: fell in Denmark 2009 characteristic noble gases Xenon-HL - diamonds Xe-S and Ne-E (almost pure 22 Ne) - silicon carbide (and graphite) further characteristic of noble gas carriers: resistance to acids
Terrestrial time-line 1964: discovery of strange Xe (now Xe-HL) 1969: discovery of Ne-E, (almost) pure 22 Ne 1975: acid-resistance of noble gas carriers 1987: identification of pre-solar diamond as carrier of Xe-HL; identification of pre-solar SiC as carrier of Ne-E and s-process Xe 1990: identification of graphite (a gas carrier) 1994: identification of pre-solar oxides (and later nitride), not carrying noble gases 2003/4: NanoSIMS: identification in situ of pre-solar silicates in interplanetary dust and meteorites
mineral isotopic signatures stellar source contribution diamond 1500 ppm Kr-H, Xe-HL, Te-H supernovae? silicon carbide 30 ppm graphite 10 ppm >50 ppm corundum/ spinel silicates silicon nitride Presolar grains in meteorites - Overview > 200 ppm 0.002 ppm enhanced 13 C, 14 N, 22 Ne, s-process elements low 12 C/ 13 C, often enhanced 15 N enhanced 12 C, 15 N, 28 Si; extinct 26 Al, 44 Ti low 12 C/ 13 C, low 14 N/ 15 N enhanced 12 C, 15 N, 28 Si; extinct 26 Al, 41 Ca, 44 Ti Kr-S low 12 C/ 13 C low 12 C/ 13 C; Ne-E(L) enhanced 17 O, moderately depleted 18 O enhanced 17 O, strongly depleted 18 O enhanced 16 O similar to oxides above AGB stars J-type C stars (?) supernovae novae SN (WR?) AGB stars J-type C stars (?) novae RGB and AGB AGB stars supernovae > 90 % < 5 % 1 % 0.1 % 80 % (?) < 10 % (?) < 10 % 2 % > 70 % 20 % 1 % enhanced 12 C, 15 N, 28 Si; extinct 26 Al supernovae 100 %
major dust factories AGB stars (low mass < 8 M sun ) and supernovae (high mass) Hertzsprung-Russell diagramm courtesy V.V. Smith
major dust factories AGB stars (low mass < 8 M sun ) after J. Lattanzio -- C-O-core (from core He burning) -- alternate He and H burning in shells 12 C, Ne-E (almost pure 22 Ne from -captures on 14 N), s-process -- (3 rd dredge up) surface; winds grain condensation
major dust factories supernovae (high mass > 8 M sun ) higher temperatures, densities higher burning phases onion shell structure explosion + explosive nucleosynthesis
Stellar History time-line forward e.g., AGB stars nucleosynthesis s-process (slow neutron capture); source of about half of the elements heavier than Fe along -stability s-process: in most cases, unstable nuclei have time for -decay before next neutron capture taken from Rolf/Rodyney 1988
neutron density in the s-process region shows up in certain isotopic ratios; where there is competition between neutron capture and -decay (branchings); e.g. krypton branching factor f n = n /( n + ) n = n = n n v th half life of 85 Kr ground state: ~ 11 a 86 Kr abundance sensitive to n density ( 85 Kr branching), 80 Kr also to temperature ( 79 Se branching) after F. Käppeler
86 Kr (and 80 Kr) production at variable n densities timescales for n capture on the order of 85 Kr half life from: Lewis et al. (1994)
Stellar History time-line forward..from nucleosynthesis that resulted in the characteristic isotopic patterns information from radionuclides with suitable half-lives required: chemical separation between parent and daughter element a favorable case: 26 Al in silicon carbide - aluminum is easily accommodated by silicon carbide, while daughter magnesium is not Mg in SiC often virtually pure 26 Mg (normal: 11%) others (restricted to supernova grains X ): 44 Ti 44 Sc 44 Ca (half-life 60 a) 49 V 49 Ti (half-life 330 d)
1 0.1 T ½ = 7x10 5 a 26 Al/ 27 Al (SiC) at time of grain formation B X supernova grains 0.01 main A 0.001 Y Z grain formation within at most few half-lives of these nuclides T ½ = 60 a from E. Zinner
most stringent constrains (supernovae) V-Ti T ½ ( 49 V)= 330 d supernova (X) SiC grains form within some months after SN explosion (Hoppe and Besmehn, 2002, ApJ)
the enigmatic diamonds the diamond story is a lot trickier than that of the silicon carbide, for two main reasons: a) lack of significant concentrations of trace elements with diagnostic isotopic features b) small size, on average 2.6 nm (~ 1000 carbon atoms) no single grain analyses 12 C/ 13 C within range of normal Solar System matter question whether all are pre-solar diagnostic elements essentially noble gases only in particular xenon and tellurium isotopically strange Xe-HL released at higher temperature than ~normal Xe-P3
HL component excesses in light (L) and heavy (H) nuclides reminiscent of p- and r-process, but % enhancement at p-only 124 Xe, 126 Xe not equal; % enhancement at r-only 134 Xe, 136 Xe not equal observed HL probably impure: high-t peak most likely a mixture of hi-t part of P3 component and pure HL (s-process free, 130 Xe 0) 150 100 50 0 Xenon-HL vs. solar wind xenon overabundance [%] r-only p-only mass number 124 126 128 130 132 134 136
HL pure the heavy part 3.5 3.0 2.5 i Xe/ 136 Xe some speculation 2.0 r-process 1.5 1.0 0.5 0.0 130 132 134 136 mass number diamond Xe clearly not the average r-process
astrophysical invention : neutron burst (intermediate between s- and r-process in He shell of exploding supernova during passage of shock wave (not needed in standard description of abundances) 1.0 i Xe/ 136 Xe 0.8 0.6 0.4 0.2 Meyer's n-burst Howard's n burst Xe-H r-process with separation mass number 0.0 128 130 132 134 136 129 131 133 135 137 better fit: classical r-process with early separation (before full decay of precursors to the stable end products) speculative
remember: nucleosynthesis of elements beyond Fe peak : predominantly by neutron capture processes (r = rapid; s = slow) along -stability taken from Rolf/Rodyney 1988
time of separation determined by crucial ratio 134 Xe/ 136 Xe 1.4 1.2 1.0 0.8 0.6 134 Xe/ 136 Xe Xe-R Xe-H precursors of 136 Xe: fast decay precursors of 134 Xe: 134 I, 134 Te with halflives of 40-50 min. required separation time: ~ 7000-8000 sec. 0.4 0.2 time [sec] 0.0 0 5000 10000 15000
Suggested possibilities how to do it (?) (1) pre-condensation (of the less volatile precursors) - requires early grain formation (2) recoil loss from grains of decay products - requires early trapping of trace elements - in -decays (?) - experimental tests (3) separation in strong magnetic field according to charge / mass (4) a combination speculative however: possible in environment of exploding supernova at such an early stage?
Celestial History how to date a presolar grain.? classical approach radioactive decay: D = daughter, P = parent element; 1, 2 = isotopes; 1= radiogenic / radioactive; 2 = stable nonradiogenic = decay constant then: D1/D2 = (D1/D2) ini + (P1/D2) (e t -1) for long-lived radioisotopes time information: -- model age (initial assumed) -- age from slope of isochrone (contemporaneous samples) = classical age dating
problem with stardust unusual isotopic compositions model age: what was non-radiogenic ratio (D1/D2) ini? isochrone age can one assume the grains have the same age? alternative (first suggested/applied by Anders and colleagues) - exposure to cosmic rays ( pre-solar cosmic ray exposure age, to be added to Solar System age for an absolute age) applied to SiC, CR production of 21 Ne from Si target
not so easy either 1. what is the abundance of non-cosmogenic 21 Ne? 2. what was the production rate (depending on flux and spectrum of cosmic rays) >4.6 Ga ago? 3. significant error in first application: recoil loss of spallation 21 Ne from µmsized grains - used curve 1 - but nuclear data on which curve I is based were not applicable and in addition an error in the application - our experiment: mean range ~2.5 µm 100 80 60 40 20 21 Ne retention [%] I I (corr) II (1 m) 0 0.1 1 grain radius [ m] II (2.5 m)
an experiment 1. take (terrestrial) SiC grains of various sizes 2. distribute homogeneously (and sufficiently separated) in a matrix where spallation does not produce 21 Ne paraffin wax paraffin wax with SiC 3. irradiate with energetic protons (1.6 GeV) 4. recover irradiated SiC, measure Ne in grains, compare with production (from 22 Na in SiC+paraffin)
later work recoil range for 126 Xe (produced on Ba and REE) determined on a Ba glass using the catcher technique: converted to SiC: ~0.2 µm 0.5 0.4 recoil range in Ba glass vs. mass difference recoil range [µm] 124 0.3 126 0.2 131 129 128 0.1 130 132 A (amu) 0.0 4 6 8 10 12 14
95 90 80 70 50 30 20 10 5 2 1 0.5 retention of spallation xenon in SiC grains retention [%] 130 Xe 128 Xe 124 Xe 126 Xe 21 Ne 0.3 1 3 grain diameter [µm] losses for Xe much less than for Ne Problem for application: how much cosmogenic Xe in SiC? depends on assumptions about p-process 124 Xe/ 126 Xe Xe data compatible with zero (!) age
most recent work / new possibilities new technology for high-sensitivity Ne analyses (ETH Zürich) supply of large (> 5 µm) SiC grains possibility of single grain analyses of grains with little loss evidence for cosmic ray effects in such large grains first seen in Li isotopes (enhanced 6 Li/ 7 Li) St. Louis calculations of recoil energy distribution by F. Wrobel DHORIN Code original aim of Wrobel s work: material science, failures in microelectronic devices several numerical data sets supplied for our work energy distribution ranges as function of size
80 60 40 20 21 Ne retention [%] Wrobel retention calculated using the Wrobel energy spectra agree very well with analytical (average) values in addition describe distribution (in particular low E, short recoil part) fix 2.5 µm 0 1 10 grain diameter [ m]
New results: Jumbo grains 100 80 60 40 20 large grains: 5-35 µm (except for one small ~ 2 µm grain; not considered here) recoil correction unproblematic 21 Ne retention [%] model Wrobel size range (except for one small grain) fix 2.5 µm grain diameter [ m] 1 10 100 in this size range: perfect agreement of recoil losses for fixed range of 2.5 µm (experiment, Morissey relation similar) and from theoretical predictions of recoil energy distribution (Wrobel)
moreover: fraction of 21 Ne that is cosmogenic is much larger than for the Lewis et al. (94) grain size separates always more than 30%, mostly >50 %, up to 97% of 21 Ne = cosmogenic choice of ( 21 Ne/ 22 Ne)-G, whether 0.00059 (Lewis et al., 1994) or 0.0033 (for maximum 18 O(,n) 21 Ne rate; Karakas et al, 2008) uncritical
for production rates in IS space commonly used: predictions of Reedy (1989) uses for flux and spectra geometric mean of the four spectra on the right (not the source spectrum; from Reedy, 1987) additional input: nuclear cross sections overall uncertainty ~ 60 % (Reedy) (?)
Another suitable element (besides Ne, He): Lithium preferred estimate of recoil based on experiments of Greiner (1975) retention (%) 100 80 60 40 retention 6 Li in SiC 6 Li-Greiner 6 Li-Wrobel 6 Li -Morissey Greiner 20 0 Morissey (C) Wrobel (Si) 0.01 0.1 1 10 100 1000 diameter [µm]
The Greiner experiment fragmentation of C, O nuclei to produce He, Li, momentum distribution ~ Gaussian isotropic in system where C,O nuclei ~ at rest important: do not integrate momentum including direction followed by calculation of recoil (result = essentially zero, error in Ray + Völ, 1983)) instead: calculate loss for given momentum and then integrate best approach: fold momentum /energy distribution with energy-range relationship recoil losses
Li and Ne ages do not agree that well only one Ne age clearly higher than 100 Ma (several, not shown, with low upper limits only); whereas many Li ages of several hundred Ma, in line with typical ages expected for IS grains need same grain analyses moreover: JUMBO grains are not typical, e.g. also low in Ne-E
Ne ages taken at face value: much shorter than estimated lifetime of interstellar grains a possible explanation inspired by Don Clayton s suggestion of a galactic merger ~ 2 Ga before solar system formation -: ~ 2 solar mass stars born during a starburst at this time would have entered the AGB (dust producing) phase shortly before formation of our Solar System
Another speculation: age of the diamonds ion implantation experiments using artificial nanodiamonds bimodal release high-t part is isotopically fractionated relative to the (unfractionated) low-t part [o/oo] a. b. c. 38 Ar/ 36 Ar 86 Kr/ 84 Kr 136 Xe/ 132 Xe 100 50 0-50 0.15 0.10 0.05 36 Ar UDD1-4 84 Kr 132 Xe % Release of gas/ o C 0.00 400 800 1200 Extraction Temperature ( o C)
apply this and correct accordingly the high-t meteorite data; leads to apparent excesses of typical cosmogenic isotopes 3 He and 21 Ne after correction for meteoroid exposure excess of ~ 200x10-8 cc/g (~ 5x10 13 atoms/g) 3 He 2.4 3 He / 4 He (x 10 4 ) 2.2 2.0 1.8 1.6 1.4 Orgueil Diamonds Leoville Diamonds Bishunpur Diamonds Fractionated He-P3 1.2 He-P3 1.0 200 400 600 800 1000 1200 1400 1600 1800 Temperature o C
remarkable: high ratio of excess 3 He to excess 21 Ne 3 He/ 21 Ne ~ 40 vs. ~10 for chondritic matter Possible solutions 1. diamonds in light-element-enriched chondritic-like matter - or diamonds in organic mantles of chondritic-like matter - or variants of this theme case of organic-enriched chondritic matter: e.g., increase C content to 70 wt % age increases factor ~4 (He, Ne consistent) however: need to take recoil also into account large size or even higher C content required for higher C even further age increase mantles: needs exquisite fine tuning organic/anorganic ratio, size of both (Ne recoil into mantles, He recoil out of)
Possible solutions 2. trapping of cosmic rays 3 He and 21 Ne are abundant secondary cosmic ray isotopes measured 21 Ne/ 20 Ne ~0.1 measured 3 He/ 4 He ~0.2 overall : 3 He/ 21 Ne in cosmic rays ~300 (!!) high ratio because 3 He produced not only by spallation of heavy (C and beyond) nuclei, but also abundantly produced from breakup of 4 He overall also: CR 3 He/proton something like 0.019 (!!) but does trapping work? 0.030 0.025 0.020 3 He / proton 0.015 0.010 energy [GeV / amu] 0.2 0.4 0.6 0.8 1.0 1.2
cosmic rays recoil nuclei what do the cosmic rays do? - imagine a setting like, e.g. a quiet molecular cloud with dispersed diamonds pass through stopped by grain stopped by gas product in grain recoil in grain pass through recoil in gas + recoils produced by reactions with gas rather than grains + recoils that leave the MC (negligible)
cosmic rays have typically energies many MeVs to GeVs will simply pass through nanodiamonds only when slowed down do something like 300 ev, can they be trapped further effect: being stopped hydrogen (gas) of ISM is ~6x more efficient than being stopped by C grains (in terms of resulting concentrations ccstp He/g gas or grain) results depend sensitively on (poorly known) low energy part of cosmic rays: Reedy (1987, 1989) mean proton spectra / inferred 3 He protons 0.1 0.01 0.001 0.0001 flux [cm -2 sec -1 ] 0-9 3 He (binned) 300-900 900-3,000 90-300 3,000-9,000 30-90 9,000-30,000 9-30 3-15 GeV energy [MeV] > 15 GeV
with the nominal values: 3 He trapping in mass layers < 0.02 g/cm² more efficient than direct production in diamond (even neglecting recoil) 3 He rate [cc / g Ma] 10-7 production in C (no recoil) 10-8 10-9 10-10 GCR trapping interestingly: such column densities in range typical for molecular clouds 10-11 depth [g / cm²] 0.001 0.01 0.1 1 10 100 1000
SUMMARY stardust in present in meteorites preserves a record of nucleosynthesis in stars,as well as processes in the ISM and the ESS (early solar system) here: concentrate on time scales nucleosynthesis: records timescales of s-process formation: from presence of extinct radionuclides (SiC and others); indication / speculation from Xe-HL for possible early SN grain formation (and destruction) pre-solar age: interaction with cosmic rays, needs knowledge of production rates and recoil losses silicon carbide: up to several hundred Ma nanodiamond: tricky, possible excesses of 3 He and 21 Ne may require association with larger carbon-rich assembly or trapped cosmic ray ³He