Transcript s-Process in low metallicity Pb stars: comparison between new theoretical results and spectroscopic

s-Process in low metallicity Pb
stars: comparison between new
theoretical results and spectroscopic
observations
Sara Bisterzo (1)
Roberto Gallino (1), Oscar Straniero (2), I. I. Ivans (3, 4), F. Käppeler (5)
and
Wako Aoki, Sean Ryan, Timoty C. Beers
Dipartimento di Fisica Generale , Università di Torino, 10125 (To) Italy
(2) Osservatorio Astronomico di Collurania – Teramo, 64100
(3)The Observatories of the Carnegie Institution of Washington, Pasadena, CA, (USA)
(4)Princeton University Observatory, Princeton, NJ (USA)
(5)Forschungszentrum Karlsruhe, Institut für Kernphysik, D-76021 Karlsruhe, Germany
(1)
VIII Torino Workshop, Granada, 6 – 11 Febr. 2006
Outline:





Lead stars (C, s, Pb rich)
C and s+r rich Lead stars
s-enhanced stars and Pb predictions
Nb: indicator of an extrinsic AGB in a
binary system
Na (and Mg): permits an estimate of the
initial AGB stellar mass.
AGB models at very
low [Fe/H]
1.2 Msun < M < 3 Msun
M = 1.5 Msun
13C-pocket:
ST*2
1.2 Msun
1.3 Msun
1.4 Msun
1.5 Msun
2 Msun
3 Msun
 3 pulses
 6 pulses
 8 pulses
 20 pulses
 26 pulses
 30 pulses
…. ST/100 Constant pulse by pulse
(ST: 4.10-6 Msun , [Fe/H] = -0.3, Reproduction of Solar Main Component )
Mass loss : from 10-7 to 10-4 Msun/yr
 Reimers
1.2 Msun
1.3 Msun
1.4 Msun
1.5 Msun
2 Msun
3 Msun
 η = 0.3
 η = 0.3
 η = 0.3
 η = 0.3
 η = 0.5
η=1
Extrinsic AGB models
Diluition factor: used to simulate the
mixing effect in the envelope of the
extrinsic stars
 M star (obs) 

dil  log 
 M AGB (transf ) 
Note:  for main sequence stars dil ≈ 0
 for giants dil may be important
[ls/Fe] versus [Fe/H]
ls = <Y, Zr>
3
M = 1.3 MΘ
2
2
1
1
3
2
M = 2 MΘ
M = 1.5 MΘ
3
3
2
M = 3 MΘ
[hs/ls] versus [Fe/H]
Example: ST/2 at [Fe/H] = -2
Example: ST/12 at [Fe/H] = -2.5
M = 1.3 MΘ
1
1
0
0
1
M = 2 MΘ
1
0
0
-1
-1
M = 1.5 MΘ
M = 3 MΘ
[hs/ls] for different masses
at [Fe/H] = -2.6
 1.5 dex
 1 dex
[Pb/hs] versus [Fe/H]
To reproduce stars with both s+r enhancements
Different choice of initial chemical
abundances of Eu in the progenitor
clouds [Eu/Fe]ini from 0.5 to 1.5 and 2.0
Effect of pre r-enrichment in s-enhanced stars
AGB star model of M = 1.3 Msun with [Fe/H] = - 2.60.
NO r-process rich
r-process rich
[Eu/Fe]ini = 0.0
[Eu/Fe]ini = 2.0
Model with pre r-enrichment normalized to [Eu/Fe]ini = 2.0 in
the parental cloud: the envelope abundances in these stars are
predicted by mass transfer from the more massive AGB
companion in a binary system which formed from a parental
cloud already enriched in r elements.
Choice of initial abundances
The choice of the
initial r-rich
isotope
abundances
normalised to Eu
is made
considering the rprocess solar
prediction from
Arlandini et
al.1999.
1- Lead stars (C, s, Pb rich)
2 – C and s+r rich Lead stars
1.
2.
3.
4.
5.
6.
J. A. Johnson, M. Bolte, ApJ 579, L87 (2002)
W. Aoki, et al., ApJ 580, 1149 (2002)
T. Sivarani, et al., A&A 413, 1073 (2004)
J. A. Johnson, M. Bolte, ApJ 605, 462 (2004)
W. Aoki, et al., PASJ 54, 427 (2002)
S. Van Eck et al., A&A 404, 291 (2003)
7. S. Lucatello, et al., AJ 125, 875 (2003)
8. J. G. Cohen et al., ApJ 588, 1082 (2003)
9. B. Barbuy, et al., A&A 429, 1031 (2005)
10. I. Ivans et al., ApJ 627, 145 (2005)
11. K. Jonsell et al., astroph 1476J (2006)
CS 22880-074 Aoki et al. 2002
Teff = 5850
HE 0024-2543 Lucatello et al. 2003
Teff = 6625
2 – C and s+r rich Lead stars
HE2148-1247 Cohen et al. 2003
M ≈ 1.3 Msun
M ≈ 1.3 Msun
0.0
With r-process enhancement
 [Eu/Fe] ini = 2.0
Teff = 6380 K
Without r-process
enhancement
 [Eu/Fe] ini = 0.0
Jonsell et al. 2006 astroph
With r-process enhancement
 [Eu/Fe] ini = 2.0
Teff = 6160
CS29497-34 Barbuy et al. 2005
With r-process enhancement
 [Eu/Fe] ini = 1.5
Teff = 4800
CS31062-050 Aoki et al. 2002
With r-process enhancement
 [Eu/Fe] ini = 1.8
Teff = 5600
Barklem et al. 2005: s-enhanced stars
** Pb predictions
12. Barklem et al., A&A 439, 129 (2005)
HE 1105+0027 Barklem et al. 2005
With r-process enhancement
 [Eu/Fe] ini = 1.8
Teff = 6132
Pb prediction  3
HE 2150-0825 Barklem et al. 2005
Without r-process enhancement
Teff = 5960
Pb prediction  3.5
[Pb/Fe] versus [Fe/H]
[Pb/hs] versus [Fe/H]
Spectroscopic Na (and Mg)  Stellar Mass prediction
AGB models
of M = 1.3, 1.5, 3 Msun,
for the same 13C-pocket,
at [Fe/H] = – 2.60.
A strong primary
production of 22Ne
results in advanced
pulses, by conversion of
primary 12C to 14N in the
H-burning ashes,
followed by 2a captures
on 14N in the thermal
pulses and implies a
primary production of
23Na via 22Ne(n,g)23Na,
(and
23Na(n,g)24Na(b-)24Mg).
Zr over Nb: Intrinsic or Extrinsic AGBs
s-process path
The s elements enhancement in low-metallicity stars interpreted by mass transfer
in binary systems (extrinsic AGBs).
For extrinsic AGBs [Zr/Nb] ~ 0. Instead, for intrinsic AGBs [Zr/Nb] ~ 1.
CONCLUSIONS:
The spectroscopic abundances of low-metallicity sand r-process enriched stars are interpreted using
theoretical AGB models (FRANEC CODE), with an
initial composition already enriched in r elements
from the parental cloud from which the binary
system was formed.
 [Zr/Nb] is an indicator of an extrinsic AGB in a
binary system: [Zr/Nb] ~ 0 for an extrinsic AGB,
[Zr/Nb] ~ – 1 for an intrinsic AGB.
 Spectroscopic determination of [Na/Fe] and
[Mg/Fe] permits an estimate of the initial AGB
stellar mass.
CONCLUSIONS:

(1)
(2)
(3)
Open Problem: the strong discrepancy of C and N
predictions with respect to observations may be
reconciled:
by introducing the effect of cool bottom process
(CBP) in the TP-AGB phase (*);
for N and [Fe/H] < -2.3, by the effect of Huge First
TDU.
Uncertainties in the spectroscopic abundances of
C, N, O, Na, Mg  M. Asplund, ARAA 2005
(*) Nollett, K. M., Busso, M., Wasserburg, G. J., ApJ 582, 1036 (2003);
Wasserburg, G. J., Busso, M., Gallino, R., Nollett, K. M., (2006), Nucl. Physics, in
press.
[hs/Fe] versus [Fe/H]
hs = <Ba, La, Nd, Sm>
3
M = 1.3 MΘ
3
2
2
1
1
3
2
1
M = 2 MΘ
3
2
1
M = 1.5 MΘ
M = 3 MΘ