sProcess in Low Metallicity Lead Stars: CEMPs and CEMPs r

1
s-Process in Low Metallicity Lead Stars CEMP-s
and CEMP-sr

• Sara Bisterzo
• University of Torino Dipartimento di Fisica
  Generale
• In Collaboration with
• Roberto Gallino, University of Torino,
  Dipartimento di Fisica Generale
• Oscar Straniero, Osservatorio Astronomico di
  Collurania, INAF, Teramo

2
Outline

• Introduction on AGB models
• 69 CEMP-s stars analyzed comparison between
  theory and observations
• Some examples
• Summary of the results

3
AGB models at very low Fe/H
1.2 Msun ? 3 pulses 1.3 Msun ? 5 pulses 1.4
Msun ? 9 pulses 1.5 Msun ? 20 pulses 2 Msun
? 26 pulses 3 Msun ? 35 pulses
1.2 Msun lt M lt 3 Msun
13C-pocket ST2 . ST/100 Constant
pulse by pulse where ST 4.10-6 Msun , Fe/H
-0.3, Used toReproduce the Solar Main Component
? Gallino et al. 1998, Arlandini et al. 1999
Mass loss from 10-7 to 10-4 Msun/yr ? Reimers
1.2 Msun ? ? 0.3 1.3 Msun ? ? 0.3 1.4
Msun ? ? 0.3 1.5 Msun ? ? 0.3 2 Msun ?
? 0.5 3 Msun ? ? 1
4
At very low metallicity

• Today, Intrinsic AGB halo stars
• typical mass is 0.6 Mo
• (initial mass 0.8 0.9 Mo)
• NO TDU (Straniero et al. 2003, 2005)
• No C or s-process enrichment observed
• Binary systems ? transfer of material C- and
  s-rich on the companion through stellar winds
  (Roche Lobe ).
• The unevolved companion shows the tipical AGB
  composition, while the true AGB star is now a
  White Dwarf.

5
Extrinsic AGB models
Diluition factor used to simulate the mixing
effect in the envelope of extrinsic stars
Note dil 0.0 dex Mstarenv(obs)
MAGB(transf) ? for main-sequence stars the
subphotospheric convective envelope mass is
Mconvenv 10-3 Mo. dil 1.0 dex Mstarenv(obs)
10 MAGB(transf) ? for giants the dilution is
important
6
Thermohaline effect

• Process which can occur in stars when AGB winds
  with higher mean molecular weight (He, C and
  s-rich material) is transferred onto the envelope
  of the observed star
• ? m-gradient
• Time scale and deep of the diffusion depends on
  the adopted model
• Two examples from the literature
• Vauclair 2004 (moderate mixing)
• 10 Mobs corresponding to dil 0.3 dex
• Stancliffe et al. 2007 (deep mixing)
• 90 Mobs corresponding to dil 1 dex
• ? Z 10-4 Zo, MAGB 2 Mo, Mobs 0.74 Mo,
  Mtransf 0.1 Mo

Other mixing processes

• Gravitational settling (Thoul, Bahcall Loeb
  1994 Straniero, Chieffi Limongi 1997),
  contrasted by Cool Bottom Process (Nollett, Busso
  Wasserburg 2003)

7
Main-sequence or turnoff stars

• No thermohaline or other mixing effects in the
  models
• Comparing observations and theoretical
  predictions, one can derive the dilution factors
  for each star
• How much does it matter
• the thermohaline effect?
• From the amount of the dilution factor it is
  possible to have an idea of the importance of
  mixing in the envelope of the observed stars

8
To reproduce stars with both sr enhancements

• Vanhala and Cameron (1998) show through numerical
  simulations how the supernova eject may interact
  with molecular cloud ? pollution with r-rich
  material
• Likely trigger the formation of the binary system
  consisting in stars with low mass
• Adopted scenario the observed star and AGB were
  formed from the same interstellar cloud, already
  enriched in r-elements

Different choices of initial r- enrichment in
the progenitor clouds r/Feini from 0.0 to 1.5
and 2.0
Spread due to inefficient mixing in the halo
Travaglio et al. (2004)
9
Star sample

• 69 CEMP-s stars analyzed, from which
• 16 are CEMP-sr and
• BUT 40 stars have not Eu detections
• 29 stars have not Pb measurements
• References
• Preston and Sneden 2001, Johnson and Bolte
  (2002), Aoki et al. (2002a,c,d,2006,2007), Van
  Eck et al. (2003), Lucatello et al. (2003),
  Cohen et al. (2003), Johnson and Bolte (2004),
  Barbuy et al. (2005), Ivans et al. (2005), Cohen
  et al. (2006), Jonsell et al. (2006), Thompson et
  al. (2007), Roederer et al. (2007), Tsangarides
  et al. (2005) PhD thesis, Barklem et al. (2005),
  Goswami et al. (2006), Masseron et al. (2006),
  Reyniers et al. (2007).

10
M 1.3 Mo ? hs/ls versus Fe/H
ls ltY, Zrgt hs ltBa, La, Nd, Smgt

• Most of the stars are from Barklem et al. 2005
  (low resolution and high errors), plus one star
  from Goswami et al. 2006 (detections problems)
• CS31062-050 Johnson and Bolte 2004 Ba/Fe 0.5
  dex higher than La,Ce,Pr,Nd,Sm/Fe
• HE0338-3945 Jonsell et al. 2006
• Ba slightly higher than hs elements,
• Y and Sr are 0.4 dex lower than Zr.
• CS 31062-012 Aoki et al. 2002
• For this star there are not good solutions for Sr
  and Y.

All these stars have hs/ls gt 0.4 (neglecting
some stars with huge errors), which means that
13C-pockets lower than ST/45 are usually excluded.
11
M 1.3 Mo ? La/Zr versus Fe/H

• Unfortunately, La is not measured in all the stars

hs/ls La/Zr CS 22183-015JB02
1.25 0.97 CS 22898-027Aoki 1.30 1.12 CS
31062-050JB04 1.56 1.27 HE 0143-0441C06
1.27 0.73 HE 0338-3945J06 1.30 1.08 Ba lines
few, strong and saturated La lines more clean
lines are available, and more accurate
experimental analysis were carried out for the
nuclear properties (Lawler et al. 2001), with
detailed informations about the different
excitation levels. For this reason, usually, I
considered La as more representative among the hs
elements (except if differently wrote in the
articles).
12
M 1.5 Mo ? hs/ls versus Fe/H

• CS 22183-015
• Johnson and Bolte 2002
• Ba/Fe 0.5 dex higher than La,Ce,Nd/Fe
• HE 1430-1123 Barklem et al. 2005
• High hs/ls but possibly solution with ST/3, s
  0.3 dex

13
M 2 Mo ? hs/ls versus Fe/H

• HE 0212-0557 Cohen et al. 2006
• Low Sr, detected with only 1 line
• HE 1430-1123 Barklem et al. 2005
• High hs/ls but possibly solution with ST/3, s
  0.3 dex

14
No MAGBini 3 Mo
hs/ls lt 0 because ls/Fe is very high
Range of the Observations
The Pb/hs predictions for M 3 Mo are very
similar to the other initial AGB masses.
15
Pb/hs versus Fe/H
16
Pb/Fe predictions versus Fe/H
Barklem et al. 2005 Aoki et al. 2007 Cohen et
al. 2006
17
Evolution phase of the stars
HE 1319-1935 (A07)
HD 196944
HE 0441-0652 (A07)
Different evolution phases Main-sequence
stars, Turnoff stars, Subgiants, Giants
CS 22183-015 Johnson Bolte 2002 Cohen et al.
2006
CS 29528-028
HE 2150-0825 (B05)
HE 0131-3953 (B05)
CS 22898-027
HE 0338-3945
18
CS 22898-027
19
CS 22898-027
20
CS 22898-027
21
HE 0338-3945
22
HE 0338-3945
23
CS 29528-028

• This star shows a
• very high s-process
• enhancement
• ls/Fe 2 dex
• hs/Fe 3 dex
• Also Na and Mg are
• the highest observed
• Na/Fe 2.33
• Mg/Fe 1.69

24
CS 29528-028

• Here the used
• dilution factors are
• dil 0.2 0.4 dex,
• according with
• a moderate
• thermohaline
• mixing effect

25
CS 22183-015 HE 0058-0244
26
CS 22183-015 HE 0058-0244
The solutions with higher mass(and higher
dilution) are not in agreement with the
observations. NO First Dredge-up episode had
occurred!
27
CS 22183-015 HE 0058-0244
No constraints about the initial AGB mass
Pb/Fe 0.4 dex higher than Cohen etal. (2006)
Fe/H 0.4 dex lower
28
HD 196944
29
HD 196944
30
HE 1319-1935
HE 0441-0652
Pbth
ST2 dil 2.4 dex
ST/2 dil 0.7 dex
lsth
Pbth
ST/12 dil 2.3 dex
ST/12 dil 0.65 dex
31
HE 0131-3953
M 1.3 2 Mo dil 0.0 1.0 dex M 1.3 Mo
seems better for Mg Pb/Feth 3
CEMP-sr rich r/Feini 1.5
32
HE 2150-0825
M 1.2 2 Mo dil 0.3 1.8 dex Pb/Feth
2 No constraint for this star about initial AGB
mass and dilution factor If hs/Fe lt 2 higher
dilution factor can be applied and low Na and Mg
are predicted
33
Two new CEMP stars

• HK-II 17435-00532
• Roederer et al. submitted
• (see talk on Thursday)
• CS22964-161
• Thompson et al. submitted
• (see talk Ivans today)

34
Summary
References Preston and Sneden (2001), Johnson
and Bolte (2002), Aoki et al. (2002a,c,d,2006,2007
), Van Eck et al. (2003), Lucatello et al.
(2003), Cohen et al. (2003), Johnson and Bolte
(2004), Barbuy et al. (2005), Ivans et al.
(2005), Cohen et al. (2006), Jonsell et al.
(2006), Thompson et al. (2007), Roederer et al.
(2007), Tsangarides et al. (2005) PhD thesis,
Barklem et al. (2005), Goswami et al. (2006),
Masseron et al. (2006), Reyniers et al. (2007),
Deroo et al. (2005).
35
Conclusions

• Main-sequence stars usually interpreted with
  lower initial mass (M 1.3-1.4 Mo) and low or
  negligible dilution factor
• Na as strong constraint for the initial AGB mass
• Low Na, and low ls/Fe observed in main-sequence
  or turnoff stars as indicator of the themohaline
  mixing efficiency

36
Problems

• Open Problems 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 ()
• 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).