The synthesis of 26Al and 60Fe in massive stars and their current abundances in our Galaxy

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The synthesis of 26Al and 60Fe in massive stars
and their current abundances in our Galaxy
Alessandro Chieffi Istituto Nazionale di
AstroFisica (Istituto di Astrofisica Spaziale e
Fisica Cosmica) Centre for Stellar and
Planetary Astrophysics Monash University -
Australia Email alessandro.chieffi_at_iasf-roma.inaf
.it
In collaboration with Marco Limongi
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Between 1979 and 2001 several experiments were
carried out
CGRO
HEAO3
R. DIEHL Clemson 2005 Astronomy with
Radioactivities V
Kretschmer et al. AA 412,47 (2003)
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On the basis of just the integrated flux towards
the galactic center, it is not possible to choose
among the various possible 26Al sources
10ltMlt30
Type II Supernovae
Confined in the spiral arms of our Galaxy
30ltMlt120
WR stars
Novae
Confined within the disk of our Galaxy
1-3ltMlt7
Intermediate mass stars
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Plüschke et al. AIP Conf. Proc. 510 ed. M.L.
McConnell J.M. Ryan p 35-39 (2000))
1.809 MeV All Sky Map
CGRO
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The 53 GhZ free-free all-sky map marks the
regions of ionized matter.
A strong ionizing flux (llt912 A) is necessary to
mantain matter ionized (otherwise it would
recombine in 1 Myr)
Only stars more massive than, say, 15 MO do
produce a strong ionizing flux
hence
The correlation between the 53 GhZ free-free and
the 1.809 MeV maps implies that they share the
same spatial distribution amd therefore that 26Al
and ionizing photons are produced by the same
stars
i.e. 26Al mainly produced by stars more massive
than 15 MO
Knodelseder (1999 - ApJ 510, 915) found also that
the scaling between the two fluxes is CONSTANT
towards all longitudes and equal to
Y26Al 10-4 MO per O7 V (Log(Qo)49.05)
RGxL 1.25 10-11 g1.8MeV / glt912A
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RHESSI and INTEGRAL launched in 2002
Reuven Ramaty High Energy Solar Spectroscopic
Imager
INTErnational Gamma-Ray Astrophysics Laboratory
R. DIEHL Clemson 2005 Astronomy with
Radioactivities V
R. DIEHL Clemson 2005 Astronomy with
Radioactivities V
60Fe/26Al
RHESSI 0.17 0.05
INTEGRAL 0.11 0.03
Diehl et al. (2006 Nature 439,5)
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Summary of the observational facts 1) 26Al is
very probably produced by stars having Mgt15 MO 2)
There are roughly 1.25 10-11 g1.8MeV per
ionizing photon at all longitudes 3) The
60Fe/26Al flux ratio is of the order of 0.14
0.05 towards the Galactic center 4) Roughly 2.8
MO of 26Al are present in the Galaxy ( 30)
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The present data have been extracted from our
latest database of evolutions of massive
stars Limongi and Chieffi (2006 ApJ 647,
483) Chieffi and Limongi (2007 in preparation)
FRANEC (release 5.050419) O.R.F.E.O. Online
Repository for the Franec Evolutionary
Output WEBPAGE http//orfeo.iasf-roma.inaf.it M
ain changes with respect to our previous
models 1) Very extended mass range gt 11 lt
M/MO lt 120 2) Mass Loss included (full WR phases
taken into account) 3) updated cross sections 4)
Mixing performed through the diffusion
formalism 5) Mixing and burning fully coupled
together and solved simultaneously
WARNING though the ground and the metastable
26Al states are properly taken into account, for
simplicity in the following Ill simply refer to
the total 26Al
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26Al production
1) H convective core
2) C (Ne/C) conv. shell (when the star
is in shell Si burning)
3) Explosive Ne burning
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26Al production in central H burning
28Si
29Si

26Al
27Al
P


25Mg
24Mg
26Mg
N
The 25Mg is the initial one (usually scaled solar)
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26Al production in the C (Ne/C) convective shell
28Si
29Si
26Al
27Al
P


25Mg
24Mg
26Mg
N
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26Al production in C (Ne/C) convective shell
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26Al production by the explosive Ne burning
The synthesis of 26Al occurs in the region where
the peak temperature drops to Tpeak 2.2 109 K
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Total 26Al yield as a function of the initial mass
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Summary of the observational facts 1) 26Al is
very probably produced by stars having Mgt15 MO 2)
There are roughly 1.25 10-11 g1.8MeV per
ionizing photon at all longitudes 3) The
60Fe/26Al flux ratio is of the order of 0.14
0.05 towards the Galactic center 4) Roughly 2.8
MO of 26Al are present in the Galaxy ( 30)
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By adopting mup 11MO Mtop 120MO a
Galactic Lyman continuum Luminosity QGAL 3.5
1053 photons/s
The galactic RGxL
The galactic 26Al
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The galactic 26Al
By adopting mup 11MO MSN I I 35MO
Mtop 120MO a Galactic Lyman continuum
Luminosity QGAL 3.5 1053 photons/s
Steady state
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g2 Velorum
Binary system containing the closest WR(11)
star Main data taken from Schaerer et al. (1997)
and Oberlack et al. (2000)
Distance 258 pc - WC8 (9 MO) - O8.5III (29
MO) 26Al(Upper limit) gt 6.3 10-5 (2.1-1.4) MO
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g2 Velorum
Binary system containing the closest WR(11)
star Main data taken from Schaerer et al. (1997)
and Oberlack et al. (2000)
Distance 258 pc - WC8 (9 MO) - O8.5III (29
MO) 26Al(Upper limit) gt 6.3 10-5 (2.1-1.4) MO
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60Fe production 1) basics
60Ni
61Ni
58Ni
62Ni
59Co
P

57Fe
56Fe
58Fe
60Fe
59Fe 44 d



N
22Ne(a,n)25Mg
Main n donor
Central He burning
rcrit 1010 n/cm3
r lt 107 n/cm3
T lt 3.5 108 K
Central C burning
r few 107 n/cm3
rcrit 3 1011 n/cm3
T lt 109 K
r gt 6 1010 to 1012 n/cm3
Shell He burning
T gt 4 108 K
r gt 6 1011 to 2 1012 n/cm3
Shell C burning
T gt 1.3 109 K
r gt 6 1011 to 2 1012 n/cm3
Shell Ne burning
T gt 1.8 109 K
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60Fe production 2) the He and C convective
shells
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60Fe production 3) the Ne explosive contribution
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The total 60Fe production
M lt 60 MO Mainly produced by the C
convective shell
M gt 60 MO Mainly produced by the C
convective shell (Ledoux criterion)
M gt 60 MO Mainly produced by the He
convective shell (Schwarz. criterion)
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The galactic 60Fe/26Al flux ratio
The 60Fe/26Al flux ratio is of the order of 0.14
0.03 towards the Galactic center
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Summary Conclusions

• Observational
• 26Al is very probably produced by stars having
  Mgt15 MO
• There are roughly 1.25 10-11 n(g1.8MeV)/
  (ionizing photon) at all longitudes
• The 60Fe/26Al flux ratio is of the order of 0.14
  0.05 towards the Galactic center
• Roughly 2.8 MO of 26Al are present in the Galaxy
  ( 30)

• Theoretical
• 26Al is mainly produced by the Ne explosive
  burning.
• 60Fe is mainly produced by the C convective
  shell.
• The observed (and quite constant) average number
  of g1.8MeV per ionizing photon (RGxL) is rather
  well reproduced by our models.
• The observed 60Fe/26Al flux ratio towards the
  center of our Galaxy is well reproduced if the
  Langer (1989) mass loss rate in the WNE,WCO is
  adopted.
• Our predictions for g2 Velorum are in agreement
  with the quoted upper limit and hence the
  longstanding discrepancy between the data and the
  predictions is removed.

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