Diapositive 1

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Production of 26Al in Wolf-Rayet ?
Ana Palacios- Institut d'Astronomie et
d'Astrophysique- ULB

• Outline
• Astrophysics with radionucleides
• Whats a Wolf-Rayet star ?
• Contribution of Wolf-Rayet stars to 26Al in
  the Galaxy

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Astrophysics with radionucleides
Radionucleides are powerfull dating
tools. Present in terrestrial meteoritic rocks,
but also in the interstellar medium and in
various other sites in the Galaxy, they trace
stellar and interstellar nucleosynthesis.
14C Anthropological timescale dating
44Ti Supernovae dating
26Al Dating the recent history of the GalaxY
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Aluminium 26

• Nucleide synthesized in the MgAl loop
• Production
• in the stellar interiors during H burning
• in explosive nucleosynthetic events
• by spallation in the ISM

Observed photons
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Aluminium 26 in the Galaxy
Emission line at 1.809 Mev
Plüschke et al. 1999 26Al distribution in the
Galaxy 9 years cumulative survey with COMPTEL
Diehl et al., AA, 298, 1995
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Production sites of 26Al
SNR
? WR
Diehl et al., AA, 298, 1995
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Production sites of 26Al
Correlation between galactic free-free emission
and emission at 1.809 Mev ? Massive stars
(cc-SNae, WR) are the main producers of 26Al Is
also produced by intermediate-mass stars (novae,
AGB)
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What is this a Wolf-Rayet star ?

• Bare core of a massive star that lost its
  hydrogen-rich envelope due to very strong stellar
  winds or to Roche Lobe overfilling
• Caracteristics
• Dense winds with v?? 1000-2000 km.s-1
• Teff gt 104 K
• X(H)surf lt 0.4
• dM/dt ? 10-510-4 M?.an-1
• Envelope exhibiting
• products of H burning
• 4He , N/C , N/O ? 12C/13C ? WN
• products of He burning
  WC
• (CO)/He gt 1 WO

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26Al ISM enrichment through WR winds
Begining of 26Al surface enrichment
Mini 40M?
Mini 40M?
Maximum production of 26Al (5x10-5)
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Effects of the initial parameters M and Z

• Predicted yields from standard evolutionary
  models for a set of 3 different metallicities
• The amount of 26Al ejected in the ISM
• ? when Z ?
• ? when Mini ?

Meynet et al, AA, 320, 1997
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Effects of the nuclear reaction rates on 26Al
production
Large incertainties on the rates implying 26Al.
26Alg(p,?)27Si
25Mg(p,?)26Alg
From the NACRE compilation, Angulo et al, Nuclear
Physics A, 1999
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Effect of the reaction rates uncertainties on
26Al production
Rates from the NACRE consortium (2000)
model 1 2 3
25Mg(p,?)26Al nom max min 26Al(p,?)27Si
nom min max
Evolution of X(26Al) in the centre

• Paradoxal effect of the optimisation of 26Al
  production from a nuclear point of view
• ? 25Mg(p,?)26Al ? ? by 2 the amount of 26Al
  reaching the surface
• ?25Mg(p,?)26Al ? 25Mg preserved ? ? the amount
  of 26Al preserved at the end of the Main Sequence
• (confirms conclusions from Meynet et al. 1997)

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Effects of rotation on 26Al production

• Observed eq. rotation velocities for O,B ? 200
  km.s-1
• Rotation ? circulation méridienne turbulence
• ?TRANSPORT OF CHEMICALS
• and
• ANGULAR MOMENTUM
• Effects of rotation on the evolution of O,B ?
• Increase of MS duration
• Early entrance in the WR phase ( ? mass loss )
• Modification of the surface chemical
  composition
• ? affects WR/O, WN/WC proportions (Meynet
  Maeder, AA, 2003)

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Effects of rotation on 26Al production
Comparison of the surface abundance of 26Al of a
60 M? star with vini 0 km.s-1 and vini 300
km.s-1 Envelope 26Al enrichment spreads over a
longer period ???26Al yields x 1.7 at Z 0.02
Vuissoz et al. Meynet, Astronomy with
Radioactivities IV, may 2003
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Combined effects of rotation and nuclear rates
uncertainties on 26Al production
Evolution of 26Al surface enrichment during the
main sequence in a 60M? , solar metallicity
? Nominal rates for 25Mg(p,?)26Alg,m Standard
vini 0 km/s Rotation prescription 1, vini
300 km/s Rotation prescription 2, vini 300
km/s Minimal rate for 25Mg(p,?)26Alg,m Rotation
prescription 2, vini 300 km/s
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Summary and Conclusions

• 26Al IS produced in WR stars to a quite large
  extent.
• The yields are sensitive to
• stellar mass
• metallicity
• 25Mg initial content
• rotation (initial rate and input physics)
• to some lesser extent, nuclear rates
  uncertainties
• By now, Z Z?, rotation seems to go in the right
  way
• But we still have improve this conclusion by
• Computing yields for different metallicities
• Introducing these outputs in evolutionary
  synthesis models