An Observational Perspective on Some Aspects of Early Stellar Nucleosynthesis

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An Observational Perspective on Some Aspects of
Early Stellar Nucleosynthesis

• Chris Sneden
• University of Texas at Austin

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My own work is a product of the collective
efforts of many people, including

• John Cowan
• Jim Truran
• Scott Burles
• Tim Beers
• Jim Lawler
• Inese Ivans
• Jennifer Simmerer
• Caty Pilachowski
• Jennifer Sobeck
• Betsy den Hartog
• Scott Burles
• George Fuller
• Anna Frebel
• Bob Kraft

• Jennifer Johnson
• George Preston
• Debra Burris
• Bernd Pfeiffer
• Karl-Ludwig Kratz
• Francesca Primas
• Sara Lucatello
• Taft Armandroff
• Andy McWilliam
• Roberto Gallino
• Bob Kraft
• Vanessa Hill
• Ian Roederer
• Christian Johnson

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Outline, of sorts

• A large literature exists on chemical
  compositions of low metallicity stars
• cant cover all topics
• trying to give a flavor of progress
• (of course) some obervational hand-wringing
• others will have to talk of premodial
  nucleosynthesis (He, Li, Be, B)
• concentrating here on
• alpha elements (Mg, Si, Ca, Ti easily done)
• neutron-capture elements
• r-process-rich
• s-process-, carbon-rich

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Bernard E. J. Pagel (1930-2007) Pioneer in
abundances, HII regions, nucleosynthesis,
chemical evolution of galaxies University of
Sussex, NORDITA
Bernard Pagel and Margaret Burbidge at a 2003
meeting Don Clayton photo http//www.astro.clemso
n.edu/NucleoArchive/
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Lets start on a good note spectroscopy yields
the solar system composition very well
Sneden Lawler 2005
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a element overabundances First Stars survey
Cayrel et al. 2004
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a element overabundances First Stars survey
Cayrel et al. 2004
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Scatter in the a elements
Giridhar et al. 2001
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Alpha-rich, alpha-poor
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Alpha-rich, alpha-poor comparison to HD 122563
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Exotic mass ranges of progenitor stars need to be
invoked
Aoki et al. 2007
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Wait some observational difficulties
Preston et al. 2006
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Plotting versus temperature reveals the problem
Preston et al. 2006
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Not a problem exclusive to one survey
Preston et al. 2006
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Be cautious with abundances derived from 1-2 very
strong lines (and above ground state)
And Si is substantially ionized
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Major work still to be done on transition
probabilities of alpha elements
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Neutron-capture elements

• s-process ß-decays occur between successive
  n-captures
• r-process rapid, short-lived neutron blast
• temporarily overwhelms ß-decay rates
• r- or s-process element origin in solar-system
• dominated by one or the other process

Rolfs Rodney (1988)
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A close look at the neutron-capture synthesis
paths different isotopes are made in r- and
s-processes
139
138
La
s,r
p
130
132
134
135
136
137
138
Ba
p
p
s,r
s,r
s,r
s
s
133
Cs
s,r
132
131
130
129
128
134
136
Xe
s,r
r
s,r
r
s,r
s
s
r-process path
s-process path
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Today we know of lots of r-process stars,
such as CS 22892-052
Note the trend
Sneden et al. 2003
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pure r-process stars good match to solar r-only
Ivans et al. 2006
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one answer Z56-82, not so for lighter elements
Ivans et al. 2006
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The de-coupling of the heavy/light r-process (?)
Johnson Bolte 2002
See also Aoki 2005, and their new astroph posting
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Now TWO solid uranium detections
Frebel et al. 2007
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And several ways to estimate ages
Frebel et al. 2007
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Credit where it belongs laboratory progress on
n-capture (Zgt30) element transitions
lighter element
n-capture, unobservable
n-capture, atomic data OK?
He
H
n-capture, recent lab transitions
Be
Li
C
B
O
F
Ne
N
Mg
Na
Ar
Al
Si
P
S
Cl
Sc
Ca
K
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
In
Sb
Te
I
Xe
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Ba
Cs
Po
At
Rn
Ra
Fr
Rf
Db
Sg
Bh
Hs
Mt
Uun
Uuu
Uub
La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Ac
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
Three groups contribute especially Lund, Liege,
Wisconsin
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Atomic structures of rare earth ions are happier
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One example of a key element hafnium
Hf
Th
Hf
Th
Ivans et al. 2006
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VERY few accessible Hf II lines
Ivans et al. 2006
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Why Hf matters begin with estimates of neutron
density ranges for the r-process
Kratz et al. 2007
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This leads to relatively constant Hf/Th
production in the r-process
Kratz et al. 2007
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And observed Hf abundances correlate well with Eu
(and La)
Lawler et al. 2007
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Where are they in the HR diagram?
Lack of many unevolved r-process stars is a
problem of line strengths?
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The Hamburg-ESO (HES) r-process survey
Here are the statistical distributions

• 253-star snapshot detailed survey (R 20,000,
  S/N 50)
• small number of n-capture elements approximate
  abundances
• stars with very strong CH bands discarded from
  sample (for now)
• 8 new stars with Eu/Fegt1.0 and 35 more with
  Eu/Fegt0.3

Barklem et al. 2005
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HES mostly r-rich stars, with a few s ones
s-only
Solar rs
r-only
Barklem et al. 2005 dashed lines are scaled
solar-system s-only abundances
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Galactic halo metal-poor stars are often
carbon-rich
Rossi et al. 2005
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C-rich stars are often Pb-rich at lower
metallicities
Van Eck et al. 2003
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The blue-metal-poor C-rich stars are simpler to
analyze
Ivans et al. 2005
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Where are they in the HR diagram?
Like globular cluster blue stragglers
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What about C-rich stars that are NOT
s-process-enhanced?
careful! NOT statistically unbiased samples
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An example of a detailed abundance pattern for an
s-rich star must have prior (?) r-process?
Ivans et al. 2005
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progress hampered by lack of lines of critical
elements
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But early appearance of vigorous r- and s-process
leads naturally to scatter in La/Eu trend with
Fe/H
The La/Eu (e.g, the s-/r-) ratio is NOT a simple
function of Fe/H
Basic trend more s-process at higher Fe/H,
but the detailed situation is complex
Simmerer et al. (2004)
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This is just to introduce some of the topics

• A large literature exists on chemical
  compositions of low metallicity stars
• Several focused talks tomorrow
• Please look at the posters for this meeting!
• We need to critically examine the Fe-peak
  elements (Z21 to 30)
• Support your local laboratory spectroscopist!
• We cannot ask theoreticians to correctly
  interpret observations that we cannot guarantee