Dredgeup efficiency and mass loss with Zeffect: - PowerPoint PPT Presentation

Title: Dredgeup efficiency and mass loss with Zeffect:


1
IS THERE A CHANCE FOR PRIMORDIAL SNeI1/2? Pilar
Gil-Pons, Jordi Gutiérrez Enrique García-Berro
We have computed and analysed the evolution of
primordial stars of ZAMS masses between 5 and 10
M?, with and without overshooting (OV), up to the
early TP-(S)AGB. The initial mass limits for the
formation of CO, ONe degenerate cores and
core-collapse SNe after the main central burning
stages have been determined. The possible final
fates of the considered stars have been explored
in the frame of the existing uncertainties.

• 1. OUR SEQUENCES
• 5 M?ltMlt10 M?, Z 0
• No OV, OV
• Gil-Pons et al (2007)

Our more massive models
The carbon burning phase with and without OV
Higher degeneracy in the case of no OV more
flashes and more violent ?
Our treatment of overshooting
Situation at the end of the main central burning
phases
Stars that do not become directly SNe develop
the TP-(S)AGB phase as stars with larger Z

• Stellar envelopes do not get much extra pollution
  
• stellar winds are weak
• and the cores grow

Our calculations yield no third dredge-up with or
without OV
Is there time enough for the stars to lose their
envelopes bef-ore their cores reach MCh?
Convection near the base of the H-rich envelope?
2. EXPLORATION OF THE FINAL STAGES

• Dredge-up efficiency and mass loss with
  Z-effect
• Reimers (1975) prescription for mass loss or its
  variation by Schröder and Cuntz (2005) favour the
  formation of SNI1/2 the stellar envelopes remain
  relatively massive when the cores reach MCh.
• Vassiliadis Wood (1993) -not in the figures,
  favour SNI1/2 even more strongly, as primordial
  stars appear relatively compact.
• Blöcker prescription allows the formation of
  SNI1/2... but only for the lowest values of ?,
  where ? represents the dredge-up efficiency

Mass loss Reimers (1975)
Mass loss Reimers (1975)

• Effects of Overshooting (OV) during the late
  evolution
• Both with and without OV SNI1/2 can form from
  initial masses of 6 M?. The calculations have
  been performed with ?0.7. When ?0.5 also the 5
  M? star also ends as a SNI1/2.
• NB These results have been obtained using and
  adaptation of the expressions for R and L by
  Izzard et al. (2004), Karakas et al. (2002). The
  authors are working on formulae specific for the
  Z0 case!

?
?
?
?
?
?
?
?
?
SNI1/2 ?
3. CONCLUSIONS
SNI1/2 ? WD ?
SNI1/2 how would they look like?

• OV decreases the initial masses that form ONe
  cores and CC SNe about 1.5-2.0 M?.
• Our calculations lead to insignificant third
  dredge-up during the early TP-(S)AGB.
• We have explored the possible final outcome of
  our stars considering the effects of OV,
  different mass-loss prescriptions and different
  third dredge-up efficiencies.
• The formation of SNI1/2 cannot be discarded!!!

• Mechanism of explosion ? like SNeIa
• But with thick H envelopes (SNII)