Abundances

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Lecture 2 Abundances
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Any study of nucleosynthesis must have one of its
key objectives an accurate, physically motivated
explanation for the pattern of abundances that
we find in nature -- in the solar system (i.e.,
the sun) and in other locations in the
cosmos (other stars, the ISM, cosmic rays, IGM,
and other galaxies) Key to that is accurate
information on that pattern in the sun. For
solar abundances there are three main sources

• The Earth - good for isotopic composition only
• The solar spectrum
• Meteorites, especially primitive ones

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The solar abundance distribution - should reflect
the composition of the ISM when and
where the sun was born
Disk
solar abundances
Elemental(and isotopic)compositionof Galaxy at
location of solarsystem at the timeof its
formation
Halo


Sun
Bulge
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History 1889, Frank W. Clarke read a paper
before the PhilosophicalSociety of Washington
The Relative Abundance of the Chemical Elements
(current, not 1889)
Current abundance distribution of elements in
the earths crust
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SOLAR ABUNDANCES
normalized to 106 Si atoms
CNO
Fe
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The solar abundance pattern
256 stable isotopes 80 stable elements
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1895 Rowland relative intensities of 39
elemental signatures in solar spectrum
1929 Russell calibrated solar spectral data to
obtain table of abundances 1937 Goldschmidt
First analysis of primordial abundances
meteorites, sun
1956 Suess and Urey Abundances of the Elements,
Rev. Mod. Phys. 28 (1956) 53
H. Schatz
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1957 Burbidge, Burbidge, Fowler, Hoyle
H. Schatz
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Since that time many surveys by e.g., Cameron
(1970,1973) Anders and Ebihara (1982) Grevesse
(1984) Anders and Grevesse (1989) - largely
still in use Grevesse and Sauval (1998) Lodders
(2003) Asplund, Grevesse and Sauval (2007) -
assigned reading
see class website
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H. Schatz
Absorption Spectra
provide majority of data for elemental abundances
because

• by far the largest number of elements can be
  observed
• least fractionation as right at end of
  convection zone - still well mixed
• well understood - good models available

solar spectrum (Nigel Sharp, NOAO)
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Complications

• Oscillator strength

Needs to be measured in the laboratory - still
not done with sufficient accuracyfor a number of
elements.

• Line width

Depends on atomic properties but also thermal and
turbulent broadening. Need an atmospheric model.

• Ionization State

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H. Schatz
Emission Spectra
Disadvantages

• less understood, more complicated solar regions
  (it is still not clear how exactly these layers
  are heated)
• some fractionation/migration effects for
  example FIP species with low first ionization
  potential are enhanced in respect to
  photosphere possibly because of
  fractionation between ions and neutral atoms

Therefore abundances less accurate
But there are elements that cannot be observed in
the photosphere(for example helium is only seen
in emission lines)
this is how Heliumwas discovered bySir Joseph
Lockyer ofEngland in 20 October 1868.
Solar Chromospherered from Ha emissionlines
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H. Schatz
Meteorites
Meteorites can provide accurate information on
elemental abundancesin the presolar nebula. More
precise than solar spectra if data in some
cases. Principal source for isotopic information.
But some gases escape and cannot be determined
this way (for example hydrogen, or noble gases)
Not all meteorites are suitable - most of them
are fractionatedand do not provide
representative solar abundance information.
One needs primitive meteorites that underwent
little modification after forming.
Classification of meteorites
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H Schatz
Use carbonaceous chondrites (6 of falls)
Chondrites Have Chondrules - small 1mm size
shperical inclusions in matrix believed to
have formed very early in the presolar nebula
accreted together and remained largely
unchanged since thenCarbonaceous Chondrites
have lots of organic compounds that indicate
very little heating (some were never heated
above 50 degrees)
Chondrule
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http//www.psrd.hawaii.edu/May06/meteoriteOrganics
.html
Some carbonaceous chondrites smell. They
contain volatile compounds that slowly give off
chemicals with a distinctive organic aroma.
Most types of carbonaceous chondrites (and there
are lots of types) contain only about 2 organic
compounds, but these are very important for
understanding how organic compounds might have
formed in the solar system. They even contain
complex compounds such as amino acids, the
building blocks of proteins.
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AGS04 Lod03
Lod03 AG89
ZAMS
ZAMS H 0.7392 0.7491
0.7110 0.7066 He 0.2486
0.2377 0.2741 0.2742
Z 0.0122 0.0133 0.0149
0.0191
gravitational settling effects included
He from Solar models Helioseismology
Emission lines H II regions
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Grevesse andSauval (1998)
quite similar to Anders and Grevesse (1989)
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Grevesse and Sauval, Spac. Sci. Rev., 85, 161,
(1998)
W
Tb
Differences between solar photospheric and
meteoritic abundances in 1998. Most
discrepancies were by then less than a factor of
30 but there were notable exceptions Tb, In,
W, Li..
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Bord and Cowley (Solar Physics, 211, 3 (2002))
Remaining discrepancies resolved for Ho, Lu, Tb
as a consequence of better atomic physics for
the spectral model. In and W remain problems. In
especially a mystery. Is it volatility or atomic
physics or both?
W
In
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Summary (Lodders 2003)

• 41 out of 56 rock forming elements, photospheric
  and meteoritic agree to within 15
• Relatively large disagreements still exist for
  elements with uncertain oscillator strengths -
  Au, Hf, In, Mn, Sn, Tm, W, and Yb - and for
  elements uncertain in meteorites - Cl, Ga, Rb
• Most discrepant are W and In
• X(4He) - protosolar - 0.2741 - 0.012
• Li depleted in sun by factor of 150. Be and B
  not depleted in the sun
• Ne and Ar are mainly from solar wind and flares
  and thus uncertain (lt 0.2 dex). Ar has been
  seen in the solar spectrum. Kr and Xe
  abundances based in part on theory (n-capture
  cross sections)

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Major recent revisions Lodders (2003) ApJ,
591, 1020 Asplund, Grevesse, and Sauval
(2007) Lower CNO abundances based upon the
non-LTE 3D hydrodynamical modeling of the of the
solar photosphere by Allende-Prieto et al
(2001), ApJL, 556, L63 and (2002) ApJL, L137.
All these papers are available on the class
website!
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Lodders (2003)
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Asplund, Grevesse, and Sauval (2004)
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Grevesse, Asplund, and Sauval (Spac Sci Rev, 130,
105 (2007))
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Solar oxygen abundance based on log H 12.0
Z
O
Anders and Grevesse (1989) 8.93
0.0189 Grevesse and Sauval
(1995) 8.83
0.017 Grevesse, Asplund and Sauval (2007)
8.66 0.0122
(3D
atmosphere non-LTE
Ni
6.23) Scott, Asplund, Grevesse and Sauval
(2009) 8.71

(revised Ni abn 6.17)
Many papers have noted that the large downwards
revision of the solar metallicity gives a sound
speed that is in discord with values inferred
from solar oscillations. See Grevesse et al
(2007) for a list.
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Grevesse, Asplund and Sauval (2007) choices for
ZAMS solar Z and He Z 0.0132 (now
0.0122) He 0.2735
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CNO
Fe
Different processes of nucleosynthesis have
their distinctive signature in the abundance
distribution.
r
s
p
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H. Schatz
Abundances outside the solar neighborhood ?
Abundances outside the solar system can be
determined through

• Stellar absorption spectra of other stars than
  the sun
• Interstellar absorption spectra
• Emission lines, H II regions
• Emission lines from Nebulae (Supernova remnants,
  Planetary nebulae, )
• g-ray detection from the decay of radioactive
  nuclei
• Cosmic Rays
• Presolar grains in meteorites

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E.g, metallicity gradient in Galactic disk
Hou et al. Chin. J. Astron. Astrophys. 2 (2002)
17 data from 89 open clusters radial iron
gradient -0.099 _ 0.008 dex/kpc
Many other works on this subject See e.g. Luck et
al, 132, 902, AJ (2006) radial Fe gradient -
0.068 _ 0.003 dex/kpc from 54 Cepheids
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From Luck et al.
Si
S
Ca
Ti
/Fe
/H
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Y
Y shows gradient Eu maybe Nd noisy La ?

La
Nd
Eu
/H
/Fe
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Variation with metallicity
Kobayashi et al, ApJ, 653, 1145, (2006)
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Kobayashi et al, ApJ, 653, 1145, (2006)
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CS 22892-052
Sneden et al, ApJ, 591, 936 (2003)
Fe/H -3.1
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Abundances in a damped Ly-alpha system at
redshift 2.626. 20 elements. Metallicity 1/3
solar Fenner, Prochaska, and Gibson, ApJ, 606,
116, (2004)
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Fenner et al (2004) vs WW95
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AA, 416, 1117
Best fit, 0.9 B, ?? 1.35, mix 0.0158, 10 - 100
solar masses Heger and Woosley 2007, in
preparation)
Data are for 35 giants with -4.1 lt Fe/H lt -2.7
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28 metal poor stars in the Milky Way Galaxy
-4 lt Fe/H lt -2 13 are lt -.26
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Frebel et al, ApJ, 638, 17, (2006) Aoki et al,
ApJ, 639, 896, (2006)
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Christlieb et al 2007, in prepartion
Fe/H -5.1
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Abundances of cosmic rays arriving at Earth
http//www.srl.caltech.edu/ACE/
Advanced Composition Explorer (1997 - 1998)
time since acceleration about 107 yr. Note
enhanced abundances of rare nuclei made by
spallation