SOME ELEMENTAL ABUNDANCES IN GLOBULAR CLUSTERS AND IN METAL DEFICIENT STARS IN OUR GALAXY Normal low

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SOME ELEMENTAL ABUNDANCES IN GLOBULAR CLUSTERS
AND IN METAL DEFICIENT STARS IN OUR GALAXY
Normal (??) low Z stars

• 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

• observational historical roots
• very large field I will sample the progress
• comparison of field and cluster stars
• others talk of lightest elements (He, Li, Be,
  B)
• Some obervational cautions
• comments on
• alpha elements (Mg, Si, Ca, Ti easily done)
• Fe-peak trends
• neutron-capture elements
• r-process-rich
• s-process-, carbon-rich

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1951, ApJ, 114, 52
"The one possibly undesirable factor in our
interpretation is the prediction of abnormally
small amounts of Ca and Fe ... Although many
workers have previously suspected the subdwarfs
of having a low hydrogen content, it appears
that, with respect to Ca and Fe at least, the
subdwarfs are rich in hydrogen.
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Another landmark paper Wallerstein et al. 1963,
ApJ, 137, 280 Red Giants with Extreme Metal
Deficiencies
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a element overabundances First Stars survey
Large stellar sample overlap with McWilliam et
al. 1995 advantages of better resolution and
signal-to-noise spectra
Cayrel et al. 2004
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a overabundances are real is the scatter also?
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The First Stars study often (but not always)
reduced star-to-star scatter
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Mostly halo cluster/field agreement
Original figure, with references is in Gratton et
al. 2004 ARAA
New globulars Carretta et al.2007 Cohen
Melendez 2005 Lee et al. 2005 Wallerstein et al.
2007 Yong et al. 2005
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One must be careful some of the scatter in some
of the elements might be artificial
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 of simple species
Often the violet 3905A line is the ONLY Si
feature detected in very metal-poor field star
AND most studies of globular cluster stars get
Si abundances only from higher-excitation Si I
yellow-red lines
And Si is substantially ionized
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But some of the scatter must be real
Giridhar et al. 2001
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a-(super)rich, a-poor comparison to HD 122563
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Proton-capture elements in clusters vary
substantially
Cluster oxygen values max-out at the field star
mean
Cluster data taken only from Lick/Texas studies
for consistency in data analysis
Field stars Carretta et al. 2000, Gratton et al.
2000
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Light element variations in clusters are obvious
Kraft et al.1997
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And correlated with each other
Kraft et al. 1997
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Na and Al positively correlate only approximately
in some cases
Johnson et al. 2005
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proton-capture reactions
p,g
20Ne
22Ne
23Na
p,a
p,g
12C
15N
16O
NeNa cycle
p,g
bn
CN cycle
T gt 40x106K
p,g
bn
bn
21Na
21Ne
22Na
T gt 10x106K
p,g
bn
13N
15O
17F
ON cycle
bn
p,g
p,g
T gt 40x106K
p,g
17O
13C
14N
24Mg
27Al
26Mg
p,g
p,g
MgAl cycle
p,g
bn
T gt 70x106K
major source
25Al
25Mg
26Al
p,g
bn
major product
(not all reaction possibilities are shown)
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A large-sample study of NGC 2808
Carretta et al. 2007
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Summary Na/O globular cluster trend
Carretta et al. 2007
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Significant Fe-peak abundance trends McWilliam
et al. 1995 Cayrel et al. 2004 (shown here)
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Fe-peak elements more cluster/field star
agreement
Original figure in Gratton et al. 2004
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Manganese trend with metallicity mimics the field
star trend almost exactly
Sobeck et al. 2006 see also a similar conclusion
for copper in Simmerer et al. 2003
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But more concerns when looking in detail Cr I
and Cr II yield different solar chromium
abundances
Sobeck et al. 2007 transition branching fraction
shown to emphasize weakness of the Cr II lines
Mismatch extends to metal-poor stars
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Neutron-capture element anomalies known to B2FH
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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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Camerons solar system r/s versus a recent
assessment
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The Hamburg-ESO (HES) r-process survey
Here are the statistical distributions
Huge Eu/Fe variation

• 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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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 et al. 2005, and their new astroph
posting
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How we can do such detailed neutron-capture
studies today progress in stellar spectra AND
in lab data
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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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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The C-rich stars are often s-process-rich and in
particular, lead-rich
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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Early evidence of vigorous r- and s-processes
explains 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! The best news this field cannot be
summarized quickly!
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Atomic structures of rare earth ions are happier
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Now TWO solid uranium detections
Frebel et al. 2007