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					Radioactivity in the
early solar system
       Maria Lugaro
     (Monash University)

     Amanda Karakas (ANU, Australia)
        Mark van Raai (Utrecht, NL)
 Anibal Garcia-Hernandez (Tenerife, Spain)
Joseph Trigo-Rodriguez (Barcelona, Spain)
                   THE PROBLEM:
                      Lee et al. 1977
                                                CaAl2Si2O8
coarse-
grained
chondrul
e


includin
g
                        (Ca,Mg,Fe)SiO3
different
mineral                                             26Al     27Al
phases                             = Al/Mg
                                                    0.7My    100%
Most primitive meteoritic inclusions, e.g.
    Calcium-aluminium rich (CAI)s +          24Mg   25Mg     26Mg

chondrules, show this “canonical” value.     79%    10%      11%
                                   high-energy
             26Al      26Mg          photons
                                 (1.8 MeV  rays)
                              • Source of energy for
                              the differentiation of
                              planetesimals (Grimm
                              & McSween 1993),
                              • which are believed to
                              be the source of much
                              of Earth’s water
                              (Morbidelli et al. 2000),
                              • with consequences on
                              the habitability of the
                              Earth.
Is the presence of 26Al special or common in young
planetary systems?
                      Radioactivity in the early Solar System:
                                      26Al
                                         ~ 4-30 times more than average
                       T1/2(Myr)
Short-living nuclei



                                       observed today in the interstellar
                      41Ca    0.10    medium (COMPTEL observations).
                      36Cl    0.3
                                       Time delay between isolation of the
                      26Al    0.7     protosolar cloud and formation of first
                      10Be    1.6    rocks ~ 1 Myr (?) 26Al > 8 times more.
                      60Fe    2.2
                                      60Fe  same or up to 300 times more
                      53Mn    5.3    than the average observed today in the
                      107Pd   9.4              interstellar medium.
                      182Hf   13     Half-life also a difficult measurement: it
                      etc.             was given as 1.5 Myr a year ago.
     Produced in the early Solar System?
                                                  The X-wind model
                                                   (Lee et al. 1998)
                                                       Irradiation by
                                                   accelerated particles
                                                   from the young Sun
                                                    results in spallation
                                                   reactions producing
                                                     radioactive nuclei.

• YES for 10Be, which cannot be made in stars, BUT 60Fe cannot be
  synthesized by spallation.
• If 26Al was produced by spallation, it could be homogeneously distributed
  only over a relatively small (~ Earth mass) rocky reservoir (Duprat and
  Tatischeff 2007).
• Recent measurements of the 24Mg(3He,p)26Al cross section exclude this
  origin for 26Al (Fitoussi et al. 2008).
                     Produced in a nearby star?
 Candidate stellar sources must:
1. Produce the right
   inventory of short-
   living radioactive
   nuclei
2. Be proposed with
   a scenario for the
   birth of the Sun
   where it is
   plausible for them
   to be there, in the
   right place and
   at the right time

The formation of the Sun is ONE event, but is it special?
         Produced in a nearby supernova?
  1. Do supernovae produce the right inventory of short-living
     radioactive nuclei?
                                                       Yes, provided it was
                                                            not a common
                                                      supernova but a faint
                                                      supernova with a lot
                                                        (~ 3 to 11 Msun) of
                                                           inner material -
                                                     containing the 56Ni that
                                                         powers supernova
                                                       light curves - getting
                                                     mixed and falling back
                                                          into a black hole.
                                                     Otherwise we get way
                                                     too much 53Mn (Meyer
(The mass location that divides the part of the star  2005, Takigawa et al.
that collapses in the remnant from the part expelled            2008).
- or injected?)
      Produced in a nearby supernova?
2. Do supernovae come with a scenario for the birth of the Sun
    where it is plausible for them to be there, in the right place
    and at the right time?
• Many solar-type stars form in the vicinity of a massive star (Orion)
• Hester and Desch 2005: low-mass stars form in the compressed gas at the
edges of H II regions produced by the ionization from massive stars and their
disks are polluted by supernova ejecta.
• By comparing the timescale of disk dissipation (< 6 Myr) to the main-
sequence lifetime, one can derive that the polluting star must have had a
minimum mass of ~40 Msun.
• The cluster where the Sun formed must have had at least 6000 members, in
order to include at least one 40 Msun star. Could planetary orbits have
remained unperturbed in such a rich cluster? (Adams & Laughlin 2001)
• From a detailed probability analysis accounting for cluster number
distribution, cluster expansion, the initial mass function, disk lifetimes, and
SNII timescales,Williams and Gaidos (2007) and Gounelle and Meibom
(2008) conclude that supernova enrichment of protostellar disks “is a
highly unlikely event, affecting less than about a 1% of all stars in the
Galaxy”.
       Produced in a nearby AGB star?
1. Do asymptotic giant branch (AGB) stars produce the right
   inventory of short-living radioactive nuclei?
    Schematic out-of-scale picture of AGB star structure.
      Monash stellar nucleosynthesis models
Proton captures at the base of
                                 Neutron captures in the
the convective envelope make
26Al via 25Mg+p
                                 thermal pulses, with 22Ne+
                                 as neutron source, make
                                 41Ca and 60Fe.




time 
  The SINS group at Monash




A group within the Centre for Stellar
 and Planetary Astrophysics (CSPA)
              Who are SINners?
• Permanent Staff
   – John Lattanzio
• Monash Fellow
   – Maria Lugaro
• Post-Docs
   – Richard Stancliffe
   – Ross Church
   – Herbert Lau
• Post-Grads
   – Carolyn Doherty
   – George Angelou
• Honorary Sinners                We have our own beer!
   – Amanda Karakas (ANU)
   – Simon Campbell (Barcelona)
   – Sandro Chieffi (Rome)
Some current specific programs
• Super-AGB stars
   – With Lionel Siess (Belgium) and Pilar Gil-Pons (Barcelona)
• Slow Neutron Capture Nucleosynthesis
   – With Sergio Cristallo, Oscar Straniero, Roberto Gallino (Italy)
• 3D Hydro in Stars
   – With Djehuty and David Dearborn and Peter Eggleton (LLNL)
   – Discovered mechanism of “deep-mixing”?
• Carbon Enhanced Metal Poor Stars (CEMPs)
   – Stancliffe on APD
• Abundances in Globular Clusters
   – Theoretical and some observational programs (with David
     Yong)
• Binary Stars and Population Synthesis
   – With Robert Izzard (Belgium) and Chris Tout (UK)
           Current Priorities
    • The Australian Network for Nuclear
            Astrophysics (ANNA)
– “Elizabeth and Frederick White Conference on
  Nuclear Astrophysics in Australia”: 23-24-25 August
  2009, Shine Dome, Canberra
– Bidding for Australia to host the 12th “Nuclei in the
  Cosmo” conference in 2012
• ASA/ANITA/SINS Summer School 2010 on
     Stellar Nucleosynthesis: 1 week for
     postgrads/postdocs in January 2010 on nuclear
reactions, theory of low-mass and high-mass stars, stellar
         abundances, meteoritic stardust grains.
       Produced in a nearby AGB stars?
1. Do AGB stars produce the right inventory of short-living
   radioactive nuclei?                      1/DIL=330
                                            t = 0.53 My ESS
     6.5 M, Z=0.02                  1.5d-02 3.2d-05 5.d-05

                                     1.0d-03 2.6d-06 2.d-06
                                                          2.d-07
                                     1.6d-04 1.5d-08 1.5.d-08

                                      Yes! Trigo-Rodriguez,
                                        Garcia-Hernandez,
                                       Lugaro, Karakas et al.
                                         2009, Meteoritic &
                                         Planetary Science
                                       (except for 36Cl which is a
                                      problem for any scenario 
                                           nuclear physics?)
          Produced in a nearby AGB star?
2. Do AGB stars come with a scenario for the birth of the Sun
    where it is plausible for them to be there, in the right place
    and at the right time?
• Shock waves from AGB winds may be capable of triggering the collapse
of the proto-solar cloud (Boss 1995).
• But the AGB scenario has been dismissed because Kastner and Myers
(1994) estimated observationally that any giant molecular cloud located
within 1 kpc of the Sun has only about a 1% probability of encountering an
AGB star in a 1 Myr period, which implies that AGB stars are relatively
rare near star-forming regions today.
• However, a detailed re-analysis of this point is needed because the
statistics of Kastner and Myers (1994) are very poor and completely
dominated by only two stars.
• Kastner and Myers (1994) also state that “There is a significant (~70%)
probability at the present epoch for a given cloud to be visited by an AGB
star in ~108 yr”. (?) If this encounter “triggers multiple star formation, then
AGB-induced proto-stars should exist in every molecular cloud” (Boss
1995).
                   Summary
• All current scenarios are problematic:
  Nucleosynthesis in the solar system is plausible,
  but does not seem to make enough radioactive
  nuclei, while stellar nucleosynthesis can make
  enough radioactive nuclei, but does not have a
  plausible scenario (...are we special?)
• 60Fe important discriminant between different
  scenarios: it seems to be made only in
  supernovae and AGB stars. Measurements are
  difficult!
• Stellar nucleosynthesis models need to be as
  accurate as (humanly!) possible and test all
  related nuclear and mixing uncertainties.
    Comparison with -ray observation of 60Fe
           in the interstellar medium
• ~ 0.3 Msun of 60Fe are        • The 60Fe/56Fe ratio in
  observed in the               the early solar system is
  interstellar medium
                                2 10-7 - 2 10-6 (?????)
  (COMPTEL+INTEGRAL
  observations)                 • The mass fraction of
                                60Fe in the solar system
• The mass of gas+dust in
  the Milky Way is ~ 5-10       is ~ 10-3 (60Fe int x2)
  109 Msun                      • So, the mass fraction
• The average mass              of 60Fe in the early solar
  fraction of 60Fe in the       system was ~ 10-10 - 2
  Milky Way ~3-6 10-11          10-9
  60Fe   in the early solar system ~ 2-140 more than the
          average observed today in the Milky Way.
           26Al   in the interstellar medium
• ~ 3.1+/-0.9 Msun of 26Al in the    • The canonical 26Al/27Al
  interstellar medium (-ray         ratio in the early solar
  COMPTEL Knödlseder 1999)
• The mass of gas+dust in the
                                     system is 5 10-5
  Milky Way is ~ 5-10 109 Msun       • The mass fraction of
                                     27Al in the solar system
• The average mass fraction of
  26Al in the Milky Way ~2-8 10-10
                                     is ~ 6 10-5 (27Al int. x2)
                                     • So, the mass fraction
                                     of 26Al in the early solar
                                     system was ~ 3 10-9
   26Alin the early solar system ~ 4-30 more than the
   average observed today in the interstellar medium.
Time delay between isolation of the protosolar cloud
and formation of first rocks ~ 1 Myr (?) 26Al > 8 more.
      Produced in the early Solar System?
• YES for 10Be, which cannot be made in stars,
• BUT 60Fe cannot be synthesized by spallation.
• Shielding of CAI cores by Fe-Mg-rich mantles is needed to get the
  right 41Ca and 26Al abundances (Gounelle et al. 2001) (
  heterogeneities?)
• If 26Al was produced by spallation, it should be homogeneously
  distributed over a relatively small (~ Earth mass) rocky reservoir
  (Duprat and Tatischeff 2007).
• Data indicates that the production of 10Be is decoupled from that of
  41Ca and 26Al (Marhas et al. 2002)

• Recent measurements of the 24Mg(3He,p)26Al cross section ( 3
  times smaller than before) exclude this origin for 26Al (Fitoussi et al.
  2008).
What about Super-AGB stars,
   Wolf-Rayet stars, ...?
• They can certainly make 26Al (Siess &
  Arnould 2008, Arnould et al. 2006)
• It seems more problematic to make
  60Fe... (if we need to make it at all!)
                                 During the s process:
                               Nn~ 107 n/cm3  (n, >>

                              Except for branching points,
                               which open for higher Nn
                                if half life > a few days




HBB
                       13C(,n)16O
           proton
           diffusion
                                         22Ne(,n)25Mg




  time 

				
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